The mass attenuation coefficient of the concrete samples without Bi2O3 and with 5 and 7 wt% bulk Bi2O3 were experimentally determined and were compared against values obtained using the XCOM and Geant4 simulations. Both methods greatly agree with the experimental values. The linear attenuation coefficients (LAC) of blank concrete (C-0), concrete with 5% bulk Bi2O3 (C-B5), and concrete with 5% nanoparticle Bi2O3 (C-N5) were determined and compared at a wide energy range. We found that the LAC follows the trend of C-0 < C-B5 < C-N5 at all the tested energies. Since both C-B5 and C-N5 have a greater LAC than C-0, these results indicate that the addition of Bi2O3 improves the shielding ability of the concretes. In addition, we investigated the influence of nanoparticle Bi2O3 on the LAC of the concretes. The half-value layer (HVL) for the concretes with bulk Bi2O3 and Bi2O3 nanoparticles is also investigated. At all energies, the C-0 has the greatest HVL, while C-N15 has the least. Thus, C-N15 concrete is the most space efficient, while C-0 is the least space efficient. The radiation protection efficiency (RPE) of the prepared concretes was found to decrease with increasing energy for all five samples. For C-0, the RPE decreased from 63.3% at 0.060 MeV to 13.48% at 1.408 MeV, while for C-N15, the RPE decreased from 87.9 to 15.09% for the same respective energies. Additionally, C-N5 had a greater RPE than C-B5, this result demonstrates that Bi2O3 NP are more efficient at shielding radiation than bulk Bi2O3.The aim of this study is to investigate the radiation shielding properties of novel concrete samples with bulk Bi Demir et al. [2O3 in both sizes (micro- and nano-size) on the radiation shielding performance of Portland cement pastes. The authors concluded that the addition of micro- and nano-Bi2O3 is an alternative method to produce lead-free radiation shielding materials.Radiation shielding tools have become increasingly more important in modern society due to the vast spread of radioactive sources in various fields of work. Workers and patients who come in contact with radiation for long periods of time are at risk of exposure to nuclear radiation, which can severely impact their health. Therefore, it is necessary to protect these people from the risks of ionizing radiation. The type of protection tools and materials chosen for a specific application depends upon several factors, which include the intensity of the photons and the energy of the radiation source. Additionally, the method used will vary depending upon the economic preparation of the materials and the resistance of the material to radiation damage ,2. Concrr et al.  evaluateMost of the previous works focused on studying the influence of the energy, the density of the concretes, and the types of aggregates added to the radiation attenuation ability of the radiation shields.By introducing nanoparticles into the composition of concretes, the radiation shielding properties of concrete can be enhanced, as well as its structural and mechanical properties. Nanoparticles improve these characteristics by improving the bulk properties or packing model structure of the concrete samples ,15. ThesWith respect to radiation shielding performance, nanoparticles are more effective than larger micro-particles due to the greater surface-area-to-volume ratio achieved by the NPs, which results in greater attenuation. This result occurs because of the more homogenous distribution caused by NPs, increasing particle density and lowering the grain size inside the material matrix. Although these effects have been postulated, these improvements are often only seen at low energies (<0.03 MeV), while at higher energies, the effect of particle size on the radiation shielding ability of the samples is minimal ,19,20.2O3 nanoparticles into cement-based composites. Within the studies that use Bi2O3 NPs, most of them evaluate the gamma-ray attenuation abilities of the Bi2O3 NP concretes, but none have tested their abilities against neutron radiation. Thus, more research is needed to understand the effect of Bi2O3 NPs content and size on the structural, mechanical, and radiation shielding properties of concrete.There is currently limited knowledge on the effect of incorporating Bi2O3 and with 5 and 7 wt% bulk Bi2O3 were experimentally determined and were compared against values obtained using the XCOM and Geant4 simulations. The LAC of blank concrete (C-0), concrete with 5% bulk Bi2O3, and concrete with 5% nanoparticle Bi2O3 were determined and compared at a wide energy range. Other shielding parameters were investigated, such as half-value layer (HVL), mean free pass (MFP), tenth value layer (TVL), and radiation protection efficiency (RPE). All of these parameters indicated that the radiation shielding for concrete improved better with bismuth nanoparticles than bismuth micro.In this work, the MAC of the concrete samples without BiTwo sets of concrete samples were developed according to the method described by Basu et al. . The mix2 after mixing, and then they were cut into slabs of 4 × 1 cm2 to be measured through the narrow beam attenuation method.The samples included fine aggregate composition with bulk bismuth oxide concentration of more than 7%, which were not succeeded. Concentrations greater than 15% of the nanoparticle bismuth oxide could not be developed. All rejected samples exhibited low compactness. The mixture composition of each sample is shown in The elemental compositions of producing samples were determined by using energy dispersive X-ray analysis EDX unit the of electron scanning microscope. The sample compositions are given in To reinforce this article, Monte Carlo Geant4 Simulation version 10.3.P3 was used. In the present work, the detector simulated at the x-plane with the same condition in the experimental work. At the top of the detector, the absorbed concrete sample was simulated. The thickness of the concrete sample was optimized according to the energy of the falling beam to avoid all photons being absorbed into the concrete sample or traversing the sample plate without reaction. The monoenergetic photons were simulated in this work to avoid the coincidence summing effect as well as to give us a broad range of energy from 0.015 up to 15 MeV ,24,25,260) with the same simulated primary photons and energy as the following equation [The run of this simulation gave the spectrum using ROOT software ,28 as shequation :(1)MAC=−x (cm) is the thickness of the concrete sample, and ρ (g/cm3) is its density.In the previous equation, 2 NaI scintillation detector and 25 cm source detector distance. The specifications of radiation sources used in this experiment in order to emit gamma radiation with various energies are given in the Samples attenuation parameters were determined by the narrow beam method ; the coli and (MAC)i are weight fractions and the MAC of the constituent elements. Experimental MAC was calculated using Equation (1). By multiplying the mass attenuation coefficient in the density ρ (g/cm3), we obtain an essential parameter called the linear attenuation coefficient or LAC (cm−1), which measures the probability of photon interaction inside the material per unit path length. The half-value layer (HVL) and the tenth-value layer (TVL) values are important attenuating factors and are defined as the thickness needed to reduce the intensity of incident photon to half- and tenth- initial values, respectively, and can be calculated using the following relations [MAC’s were estimated theoretically using the “mixture rule” and the XCOM computer software developed by NIST. The mixture can be expressed by the following relation :MAC = Ʃ elations .(3)HVL=The mean-free path or MFP (cm) is the reciprocal of attenuation coefficient and is also defined as the average distance between two successive interactions of gamma rays inside the sample material, which can be estimated by Equation (5).The shielding efficiency of an absorber sample can be investigated using a parameter called the radiation protection efficiency (RPE), which depends on the net count rate (intensity) with and without the absorber during the measurement and is given by Equation .(6)RPE=1% and given by:The mass attenuation coefficient of the concrete samples  was experimentally determined and was compared against values obtained using the XCOM and Geant4 simulations see . First, 2% and given by:All of these values are within less than ±2% deviation, with the greatest difference equal to −1.97% and the least to 0.19%. These results indicate that the experimental and XCOM results strongly agree with each other, confirming the accuracy of the experimental values. Additionally, the percent difference between the experimental and the Geant4 simulation was also calculated and is represented by ∆2/g at 0.060 MeV to 0.1194 cm2/g at 0.245 MeV, 0.0765 cm2/g at 0.662 MeV, 0.0585 cm2/g at 1.173 MeV, and 0.0541 cm2/g at 1.408 MeV. This decrease occurs since higher energy photons have an easier time penetrating through the samples, decreasing MAC. The MAC values of the samples can also be compared against each other. At all energies, the MAC results follow the order of C-0 < C-B5 < C-B7. More specifically, at 0.344 MeV, for example, the MAC values are equal to 0.1016, 0.1068, and 0.1049 cm2/g for C-0, C-B5, and C-B7, respectively. These results indicate that the C-B7 sample has the greatest MAC out of these three samples, meaning it has the best shielding ability at all the tested energies.For these values, all the results were within a deviation of less than ±1.2%, which is closer than the XCOM values, indicating that the Geant4 values agree with the experimental values more than the XCOM results. Nevertheless, both methods greatly agree with the experimental values. In addition, the MAC values can be analyzed against increasing energy. In this case, all the values decrease with increasing energy. For instance, for the C-0 sample, its experimental MAC values decrease from 0.3754 cm2O3, and concrete with 5% nanoparticle Bi2O3 were determined at a wide energy range and plotted in −1 for C-0, 0.213 cm−1, and 0.230 cm−1 for C-N5. Since both C-B5 and C-N5 have a greater LAC than C-0, these results indicate the addition of Bi2O3 improves the shielding ability of the concretes. It is well known that the LAC has a direct relation with the density of the medium [The linear attenuation coefficients (LAC) of blank concrete (C-0), concrete with 5% bulk Bie medium . Additio2O3 on the LAC of the concretes. Samples with 5, 10, and 15% Bi2O3 were selected to observe the effect of increasing the nanoparticle Bi2O3 concentration on the shielding ability of the concretes. At all energies, the LAC values have the trend of C-N5 < C-N10 < C-N15. At 0.245 MeV, for instance, the LAC values increased from 0.381 to 0.418 and 0.472 cm−1 for C-N5, C-N10, and C-N15, respectively. These results demonstrate that increasing the amount of nanoparticle Bi2O3 improves the shielding ability of the concrete. Furthermore, the influence of Bi2O3 on the LAC values is clearer at low energies. For example, at 0.0595 MeV, C-N5′s LAC was 1.39 cm−1, C-N10′s LAC was 1.70 cm−1, and C-N15′s LAC was 2.11 cm−1. This trend can be understood according to the domination of photoelectric process. At higher energies, meanwhile, the effect of Bi2O3 on the shielding ability of the concretes is minimal, and the difference between their capabilities of the samples is small. This is a result of the domination of Compton scattering which has a weak dependence on the chemical composition of the medium. The LAC values at 1.41 MeV are equal to 0.155, 0.158, and 0.164 cm−1 for C-N5, C-N10, and C-N15, respectively. Nevertheless, at all energies, the C-N15 sample had the greatest LAC out of these three samples.2O3, it can be seen that the HVL for the concrete with NP Bi2O3 is lower than that of bulk Bi2O3, which means that the use of NPs decreases the thickness of the concretes and improves their ability to shield photons.The half-value layer (HVL) is an important radiation shielding parameter ,37,38,39The mean free path (MFP) for the C-0, C-B5, and C-N5 concretes are illustrated against increasing energy in 2O3 and 5% NP Bi2O3, with the NP Bi2O3 having the lowest TVL at both energies. It was also found that this trend is maintained at all the tested energies; thus, only these two energies were graphed. 2O3 to the concretes improve their shielding ability. Additionally, C-N5 has a greater RPE than C-B5, this result demonstrates that Bi2O3 NP are more efficient at shielding radiation than bulk Bi2O3. As the Bi2O3 further increases, the RPE values increase with it, meaning that increasing the Bi2O3 content in the concrete enhances the attenuation capability of the samples.The radiation protection efficiency (RPE) of the prepared concretes were graphed against increasing energy in 2O3 and with 5 and 7 wt% bulk Bi2O3 were experimentally determined and were compared against values obtained using the XCOM and Geant4 simulations. Both techniques greatly agree with the experimental results, implying the accuracy in the setup used for the determination of the MAC and LAC for the fabricated concretes. The LAC of blank concrete (C-0), concrete with 5% bulk Bi2O3, and concrete with 5% nanoparticle Bi2O3 were determined and compared at a wide energy range. From the obtained results, the following conclusions can be drawn:2O3 improves the shielding ability of the concrete since the LAC values have the trend of C-N5 < C-N10 < C-N15.The LAC results demonstrated that increasing the amount of nanoparticle BiAt all energies, the C-0 has the greatest HVL, while C-N15 has the least. Thus, C-N15 concrete is the most space efficient, while C-0 is the least space efficient.The MFP is evaluated for C-0, C-B5, and C-N5 concretes and the MFP values at 0.662 MeV are equal to 4.78, 5.07, and 5.25 cm for C-0, C-B5, and C-N5, respectively, which demonstrated that the C-N5 sample has the best shielding ability out of these three concretes.The radiation protection efficiency (RPE) of the prepared concretes was found to decrease with increasing energy for all five samples.2O3 NP are more efficient at shielding radiation than bulk Bi2O3.The RPE results revealed that increasing the energy of the photons leads to decreased capability for these concretes to shield the incoming radiation. Finally, C-N5 has a greater RPE than C-B5; this result demonstrates that BiIn the present work, the MAC of the concrete samples without Bi


Images were interpreted by visual evaluation and semi-quantitative analysis. In semi-quantitative analysis, the maximum standard uptake value (SUVmax) of the target and gray matter was measured and the target uptake/gray matter uptake (T/G) ratio was calculated.13N-ammonia were significantly higher in PGR than RPA , whereas the T/G ratios of 11C-MET were obviously lower in PGR than RPA . Using the canonical discriminant analysis, we calculated the predicted accuracy of RPA (100%), PGR (92.9%), and the overall predicted accuracy (96.43%).The T/G ratios of 13N-ammonia and 11C-MET PET/CT is valuable in the differentiation of RPA from PGR after trans-sphenoidal adenomectomy.The combination of  This study was approved by the hospital ethics committee and the need for signed informed consent was waived.We retrospectively reviewed the data of suspected RPA  patients who underwent 13N-ammonia and 11C-MET were produced in our department by commercially available systems for isotope generation  with standard methods. The radiochemical purity was>99%. PET/CT scans were performed with a Gemini GXL-16 scanner . Five minutes after intravenous injection of 7.4 MBq (0.20 mCi)/kg 13N-ammonia or 11C-MET, a 10-min serial PET/CT scan using a brain imaging protocol  was initiated. Images were attenuation-corrected with low-dose CT and reconstructed with the Line of Response RAMLA algorithm. 13N-ammonia and 11C-MET PET/CT were performed with an interval of at least 24 h.PET images were interpreted by two experienced nuclear physicians independently and reached a consensus.11C-MET PET/CT images was considered positive.The uptake of the targets was classified into 3 degrees visually compared to the surrounding normal brain tissue: low uptake, moderate uptake, and high uptake. Moderate and high uptake on For each patient, a region of interest (ROI) over the entire target was drawn on the transaxial plane referred to MRI or computerized tomography (CT) images, and the maximum standardized uptake value (SUVmax) was measured. Then another referenced ROI (approximately 10 mm in diameter) was drawn on the normal gray matter of the left prefrontal cortex, gaining the target uptake/gray matter uptake (T/G) ratio.t-test for each tracer. Second, the T/G ratios of the two tracers were adopted as multiple variables in the canonical discrimination analysis. By obtaining the canonical discriminant function, each patient could be successfully classified into one group according to the functional result. Finally, cross validation was performed. P < 0.05 suggested that difference had statistical significance.Statistical analysis was performed using SPSS 20.0 software . Measurement data were expressed in form of mean ± standard deviation (SD). First, the T/G ratios of RPA and PGR were compared using Student’s PGR was identified in 14 patients with PET and could not be identified by any other imaging modality in 5 patients. Of the 14 patients, 8 were determined to have normal function, and 6 were determined to have hypopituitarism. The diameter of RPA ranged from 1.0 to 4.2 cm (1.83 ± 0.73 cm).13N-ammonia PET images and 1 (5.26%), 18 (94.74%) patients were graded as low and high uptake respectively on 11C-MET PET images.For the 19 patients with RPA, 14 (73.68%), 3(15.79%), 2(10.53%) patients were graded as low, moderate, and high uptake respectively on 13N-ammonia PET images and 8 (57.14%), 5 (35.71%), 1 (7.14%) patients were graded as low, moderate and high uptake respectively on 11C-MET PET images.For the 14 patients with PGR, 2 (14.29%), 12 (85.71%) patients were graded as moderate and high uptake respectively on Of the 19 patients with RPA, MET was positive in 18 patients (18 true positive) and negative in 1 patient  compared to histological results.13N-ammonia were significantly higher in PGR than RPA , however, the T/G ratios of 11C-MET were obviously lower in PGR than RPA  . The predicted accuracy of RPA (100%), PGR (92.9%) and the overall predicted accuracy (96.43%) were calculated. As a result, only 1 PGR was misdiagnosed as RPA , probably because FDG uptake is related to tumor malignancy or aggressiveness rather than hormonal production and secretion [For patients after trans-sphenoidal pituitary adenomectomy, postoperative follow-up by clinical and imaging methods remains necessary. To our knowledge, MRI is an excellent imaging modality and the top choice in the assessment of pituitary lesions. However, considering the morphological changes of the postoperative area and the confusion about the anatomical structures, MRI is often unable to distinguish RPA from PGR –6, 15. Iecretion . Its uti13N-ammonia demonstrated higher uptake in PGR than RPA and 11C-MET had higher uptake in RPA compared with PGR. Thus, 13N-ammonia PET played a better role in the identification of PGR, whereas 11C-MET PET seems more useful in the detection of RPA.In our study, 13N-ammonia is not only a good indicator of the blood flow of the pituitary gland, but also a potential tracer to indicate glutamine synthesis metabolism, as reported in our previous studies [13N-ammonia due to the absence of the blood-brain barrier (BBB), high regional cerebral blood flow (CBF), and high capillary permeability surface area product [13N-ammonia is comparable to MRI [13N-ammonia could exhibit potential value when MRI findings were negative. Besides, 13N-ammonia is also a promising imaging method to reflect the pituitary function. Hypopituitarism showed decreased 13N-ammonia uptake and could be diagnosed in the early stage [13N-ammonia images. studies –22. Pitu product  As for de to MRI . Even in11C-MET PET/CT in identifying pituitary tumors has been reported in previous studies [11C-MET PET/CT in recurrent adenomas regardless of the tumor size and the endocrine subgroups [11C-MET was very high in this investigation for RPA (18/19), even in nonfunctional adenomas, which was in accordance with previous studies [11C-MET due to extensive cystic degeneration within the tumor. Conversely, PGR showed minimal uptake on 11C-MET images. Sex, age, and the menstrual cycle in women can influence the accumulation of 11C-MET in the remaining pituitary tissue. Occasionally, the 11C-MET uptake in pituitary gland can be confused and result in false positive results. Besides, RPA is not always identified with high uptake because of necrosis, cystic degeneration and hemorrhage. To avoid this phenomenon, another imaging comparison has been suggested to identify residual pituitary tissue [13N-ammonia to locate the pituitary gland based on our previous studies [13N-ammonia was combined with 11C-MET, the differential accuracy of these 2 clinical entities was 96.43%. By accurately locating RPA and PGR, 13N-ammonia and 11C-MET PET can guide surgery and realize the maximal protection of pituitary function. 68Ga 1,4,7,10-tetraazacyclododecane-N, N′, N″, N″’-tetraacetic acid-D-Phe1, Tyr3-octreotate (DOTATATE), a novel somatostatin analog, can also be applied in the recognition of remaining pituitary tissue. The accumulation was only lower than that in spleen, kidneys, and adrenal glands [68Ga-DOTATATE.The usefulness of  studies , 11, 24.ubgroups , 10, confor RPA 1/19, eveny tissue . We sele studies –22. Whenl glands , 27. HowOne major limitation of the study is that we did not provide the uptake information of scar tissue. Scar tissue may form at the post-operative site, particularly after graft implantation. Although the scar tissue should have no or minimal metabolism as predicted in previous study , caution13N-ammonia and 11C-MET PET/CT is valuable in the differentiation of RPA from PGR after trans-sphenoidal adenomectomy.The combination of


Research suggests that many sheep farmers continue to carry out traditional antibiotic use practices despite new ’good practice’ recommendations. The aim of this study was to group farmers depending on their attitudes around antibiotic use and antibiotic resistance, and determine the behaviours that are associated with the farmers in these groups. In 2017, a flock health survey was sent to British sheep farmers. K-means cluster analysis was used to identify groups of farmers with similar attitudes towards antibiotic use and resistance. A multivariable logistic regression model was built to determine the associations between farmers’ past behaviours and their antibiotic attitude group. There were 461 responses. Two groups of farmers were identified based on their antibiotic attitudes. Cluster 1 were defined as the "discordant" group who had positive views of using antibiotics prophylactically and negative views of reducing antibiotic use. Cluster 2 were defined as the "concordant" group who were positive about reducing antibiotic use and had negative views about using antibiotics prophylactically. Using antibiotics in all lambs , using antibiotics in all ewes , always trimming diseased feet over the past three years , not using a computer to record information over the past three years , not changing worming practices over the past three years , and farmers’ perceptions that their sheep flock did not make a financial loss in the past three years  were significantly associated with belonging to the discordant group. Talking to their veterinarian about antibiotic use or the frequency of veterinary visits were not associated with antibiotic attitude group. These results suggest that farmers who had attitudes relating to antibiotic use that did not align with current recommendations carried out more traditional practices, which were strengthened by their positive perceptions of profitability. In light of the global antibiotic resistance crisis, measures are being taken to ensure the prudent use of antibiotics, with a particular political interest in reducing avoidable use in agriculture .There arQuantification of antibiotic use in the sheep sector is challenging as sheep producers often have additional enterprises such as beef production, which makes it difficult to distinguish what species a drug has been used in. Additionally, until recently, there was no central location for sheep antibiotic usage data to be collated in the UK. The Royal College of Veterinary Surgeons legislation states that antibiotics on UK farms must be prescribed by a veterinarian who has the animals ‘under their care’ . Many shWhilst antibiotic use is thought to be low on sheep farms ,9, thereAs highlighted in The Responsible Use of Medicines in Agriculture Alliance (RUMA) reports, one of the "hotspots" where antibiotic use could be reduced in the sheep sector is neonatal lamb diseases, such as watery mouth (colibacillosis) and joint ill (suppurative polyarthritis) . HistoriChlamydia abortus and Toxoplasma gondii, antibiotic use for the control of abortion is often deemed unnecessary [The routine use of antibiotics in pregnant ewes to prevent abortion is also considered to be a ‘hotspot’ for unnecessary use . As vaccecessary . Managemecessary . The chaMost research into farmer antibiotic use behaviour focusses on the way farmers’ attitudes influence their behaviour ,22. ThisThere is evidence that the association between attitude and behaviour is bidirectional and that behaviours can influence attitudes. This is particularly the case for undesirable behaviours such as smoking  and bingIn this introduction we have considered multiple antibiotic practices that farmers continue to carry out despite new ’good practice’ recommendations. The aim of this study was to group farmers depending on their attitudes around antibiotic use and antibiotic resistance and then determine the behaviours that are associated with the farmers in these groups.The survey was developed as part of a larger project and was designed by EL, JK and FL and the survey design has previously been described in detail . This paThis section included questions on the farmer’s characteristics such as age, number of years farming sheep and level of education. The farm characteristics included number of mature ewes, production system type and size of farm. Farmers were asked whether their sheep flock had made a profit, loss or broken even over the past three years. They were also asked if they had changed any farm practices over the past three years.Respondents were asked about their management practices related to lameness control. This included vaccination against footrot, time from observation to treatment of lame sheep, foot trimming, use of antibiotic injection, use of foot spray and separation of lame sheep.Other questions related to health management and performance were worming of lambs and ewes, culling practices, and data recording practices. Frequency of advice from a veterinarian was included.Farmers were asked about the proportion of lambs they treated with antibiotics for the treatment and prevention of watery mouth, joint ill and cases of ill lambs (e.g. pneumonia) in the lambing season between September 2016 and August 2017. They were asked about the type of antibiotic given which included oxytetracycline injectable, white injectable (e.g. penicillins), other injectable, oral antibiotics and antibiotic pills. Photographs and manufacturer names of antibiotics were included in this section for clarification. Farmers were also asked about the proportion of ewes they treated with antibiotics for the treatment or prevention of abortion, problems around lambing, lameness, illness (e.g. pneumonia) and mastitis.Respondents were asked to rate a series of sixteen statements around attitudes toward antibiotic use and resistance, from 1 = Strongly disagree to 5 = Strongly agree. A don’t know option was also available to select. The statements were informed from the wider literature on attitudes towards antibiotics ,33,34.The distribution of this survey has been previously described in . The tarThe study was approved by the University of Nottingham School of Veterinary Medicine and Science Ethics Committee (no 1850 160916).Data cleaning and data analysis including descriptive statistics, cluster analysis and logistic regression were carried out in Stata 16 . Where there were duplicate entries from the same farm, the most complete response was kept for analysis. General descriptive results from this survey have previously been published . HoweverCluster analysis was performed to identify groups of farmers with similar attitudes towards antibiotic use and resistance. The farmers were grouped based on their ratings of the sixteen statements relating to antibiotic use and resistance, from 1 (strongly disagree) to 5 (strongly agree). A small proportion (0.7–5.4%) of "don’t know" responses were reported for nine statements. Any “don’t know” responses were recoded as 3  for cluster analysis. Cluster analysis was also run with the "don’t know" responses removed and there was no significant differences in the results. Therefore, the set of responses with "don’t know" coded as neutral were used as less respondents were removed from the analysis. Four respondents were removed at this stage because of missing ratings for the statements.n observations into k clusters. A limitation of k-means cluster analysis is that the number of clusters must be defined a priori [K-means clustering uses an iterative algorithm to partition a priori . Therefoa priori . This esThe dependent variable of interest for the multivariable logistic regression was the antibiotic attitude cluster group, where 1 was the "discordant group" whose attitudes did not align with current antibiotic use recommendations (e.g. thinking that using antibiotics for prevention was acceptable) and 0 was the "concordant group" whose attitudes did align well with current antibiotic recommendations. Potential independent variables were those relating to past and current management practices. New variables were created for past practices by inspecting farmers’ responses relating to changes in management practices. If farmers selected that they had not changed any practices over the past three years, then it was assumed that the practices stated by farmers in the survey were carried out for the past three years. A univariable analysis was carried out and variables with p≤0.1 were considered for the multivariable analysis. A forward selection stepwise model building approach was used, where only variables with p≤0.05 were selected to remain in the model. The multivariable logistic regression model took the form of:icluster group is the antibiotic attitude cluster group the ith farmer belongs to, iμ is the fitted probability of the outcome, α is the intercept, iβ is the vector of coefficients corresponding to the vector of predictor variables ix.Where The Hosmer-Lemeshow test was carried out to test model fit. The Variance Inflation Factor (VIF) and the tolerance were inspected for collinearity between variables.A total of 461 usable responses were received, resulting in a 55.5% useable response rate. Of the respondents, 43.7% (200/461) were aged between 36 and 55, 40.8% (187/461) were aged over 55 and the remaining 15.5% were under 35 years old (71/461). Most farmers housed their sheep at lambing time .The median flock size of farms was 520 (IQR 300–830), and the median grassland area used for sheep was 258 acres (IQR 150–480). Three quarters of sheep farmers also kept beef cattle . The median number of breeding female beef cows kept was 18 (IQR 0–50) and the median number of other cattle kept was 40 (IQR 0–90). The characteristics of the farm and farmer are presented in Over the past three years, 11.7% (54/461) of farmers thought that their sheep flock made a financial loss, 33.4% (154/461) thought they were at breakeven point and 45.3% (209/461) thought that they made a profit.Over the past three years, 53.4% (246/461) of farmers had not changed any management practices on their farm, 21.3% (98/461) had made changes to their culling practices, 18.7% (86/461) had made changes to their recording practices, 26.3% (121/461) had made changes to their worming practices, and 17.1% (79/461) had made other changes to their management practices.2  =  66.175, p<0.001).To investigate the changes in worming practices further, chi-squared tests were conducted to identify differences in worming practices between those who changed their practices and those who did not. A chi-squared test indicated that the proportion of farmers using faecal egg counting to judge whether lambs needed worming was significantly different for farmers who had changed their worming practices compared to those that had not  of farmers never sought advice about their flock from a veterinarian, 29.3% (135/461) sought advice just once, and 64.2% sought advice at least quarterly (296/461).Just over half of farmers reported that they had talked about antibiotic usage with their veterinarian between September 2016 and August 2017 , and just over a quarter that they had talked about antibiotic resistance with their veterinarian . Many farmers reported that they had not talked about either antibiotic use or resistance with their veterinarian .Only 2% (9/461) of farmers thought their antibiotic use was higher than usual between September 2016 and August 2017. Most farmers thought their antibiotic usage was roughly the same as usual , and the remaining 29.3% (135/461) of farmers thought their antibiotic usage was lower than usual.Around half of farmers thought their antibiotic use was less than other sheep farms . Most of the remaining farmers thought that their antibiotic use was approximately the same as other sheep farms  and three farms thought their antibiotic use was higher than other farms.Twenty-two percent (102/461) of farmers used antibiotics for prevention of watery mouth, joint ill or illness in all of their lambs, whereas 8.5% (39/461) of farmers used antibiotics for prevention of disease in all ewes.Respondents were clustered into two groups related to the rating of seventeen statements around antibiotic use and antibiotic resistance. The means of how each group rated the statements are presented in A multivariable logistic regression model was built to estimate the associations of farmer practices and behaviours on belonging to the discordant antibiotic attitude group. The results are reported in The odds of belonging to the discordant group doubled when farmers did not use a computer to record information compared with farmers who used a computer for the past three years , when farmers had not changed their worming practices in the past three years compared to farmers who had changed their worming practices  and when farmers reported that their sheep flock did not make a financial loss in the past three years .Farmers who used antibiotics for prevention of disease in all lambs born on their farm in the previous year had 2.689 times higher odds of belonging to the discordant group compared to farmers who did not use antibiotics in all their lambs . Farmers who used antibiotics for prevention of disease in all ewes on their farm in the previous year had 3.388 times higher odds of belonging to the discordant group compared to farmers who did not use antibiotic in all their ewes . Farmers who always trimmed diseased feet for the past three years had 2.487 times higher odds of belonging to the discordant group compared to farmers who did not always trim diseased feet . Farmers who thought that they used the same amount of antibiotics as other sheep flocks had 2.495 times higher odds of belonging to the discordant group compared with farmers who thought that they used less antibiotics than other sheep flocks .The Hosmer-Lemeshow test gave a p-value of 0.5, indicating that the model fit the data well. The VIF and tolerance values of the variables used in the logistic regression indicated that there were no collinearity problems.A second model included the same variables with the same positive or negative associations as model presented in This is the first study to investigate how farmers’ past behaviours may be associated with their attitudes towards antibiotic use. The results suggest that farmers could be clustered into two different groups based on their antibiotic attitudes. The "discordant" group were more likely to have negative views of reducing antibiotic use and positive views of using antibiotics for prevention, and therefore have attitudes that are discordant with current antibiotic use recommendations. The "concordant" group were more positive about reducing their antibiotic use and had negative views about using antibiotics for prevention. Belonging to the discordant group was associated with carrying out traditional practices, whereas belonging to the concordant group was associated with carrying out modern practices and recently changing their practices.The existence of the discordant group of farmers may be explained using the theory of cognitive dissonance within the free choice paradigm, where a decision is freely made by an individual . Once a Other traditional practices, such as trimming sheep feet and not changing anthelmintic use, were also associated with belonging to the discordant group. Trimming sheep feet to treat and control lameness is an age-old practice that has been passed down through the generations of farmers . HoweverOver half of farmers had not changed any of their farm practices in three years, suggesting that their farm practices may have become habitual over the years. When a behaviour is repeated in a consistent context, automaticity increases . For exaThe farmers who did not use a computer to record farm information for the past three years were more likely to belong to the discordant group. Electronic recording is a relatively modern practice in sheep farming; for example, electronic identification of sheep became mandatory in the EU in 2010 . Use of Farmers who perceived that they did not make a loss from their sheep flock in the past three years were more likely to belong to the discordant group. Although on average sheep and beef farmers typically make smaller profits than other farming businesses, productivity is an important goal of any farm business . AccordiFarmers who believed that their antibiotic use was the same as other farms were more likely to belong to the discordant group. Therefore, farmers in the discordant group may think that the way they perceive antibiotic use is similar to other farmers (i.e. a descriptive norm). This is similar to findings in a study of dairy farmers, where perceived norms around mastitis treatment hindered appropriate antibiotic use . FarmersThe frequency of veterinarian advice and whether the farmer reported that they had specifically spoken with their veterinarian about antibiotic use were not significantly associated with farmers’ antibiotic attitude group. This may be because veterinarians were not obviously speaking with farmers about appropriate antibiotic use at the time of the study. Studies from pig, poultry and dairy sectors found that veterinarians were a key source of information on antibiotic use for farmers ,34,58. TThe median number of ewes was larger in the survey population than the national average  and may One potential way of achieving recommended behaviours is through sharing positive attitudes towards antibiotic stewardship . For thoThere are several initiatives to promote responsible antibiotic use. For example, the Antibiotic Guardian campaign is a worldwide information campaign to increase engagement and awareness of antibiotic resistance in healthcare professionals and the public, including farmers . In the Behaviours could also be changed by targeting farmers’ self-identity. We suggest that past behaviour may infer farmers’ self-identity as a traditional or good farmer . When a Overall, farmers who had antibiotic attitudes that were discordant with current antimicrobial use recommendations carried out more traditional practices, which was strengthened by their positive perceptions of their profitability. This may be explained by cognitive dissonance theory where farmers matched their attitudes to the behaviours they carried out. Additionally, habit may play an important role in farmers having attitudes that did not align with optimal antibiotic use recommendations; whereas veterinary contact did not influence farmers’ attitudes towards antibiotics. These results suggest that potential behaviour change interventions focussed on refining antibiotic use should challenge habitual behaviours through targeting farmers’ self-identity, disrupting the contextual cues of antibiotic use and improving positive attitudes towards antibiotic stewardship.


Fiber-reinforced concrete (FRC) is a competitive solution for the durability of reinforced structures. This paper aims to observe the moment redistribution behavior occurring due to flexural and shear loading in Glass Fiber-Reinforced Polymer- (GFRP) reinforced continuous concrete beams. A rectangular cross-section was adopted in this study with dimensions of 200 mm in width and 300 mm in depth with a constant shear span-to-depth ratio of 3. The reinforcement ratio for the top and bottom were equal at sagging and hogging moment regions. A finite element model was created using Analysis System (ANSYS) and validated with the existing experimental results in the literature review. Based on the literature review, the parametric study was conducted on twelve beam specimens to evaluate the influence of concrete compressive strength, transversal GFRP stirrups ratio, and longitudinal reinforcement ratio on the redistribution of the moment in beams. Several codes and guidelines adopted different analytical models. The Canadian Standards Association (CSA) S806 adopted the modified compression field theory in predicting the shear capacity of the simply supported beams. Recently, various researchers encountered several factors and modifications to account for concrete contribution, longitudinal, and transverse reinforcement. A comparison between the predicting shear capacity of the generated finite element model, the analytical model, and the existing data from the literature was performed. The generated finite element model showed a good agreement with the experimental results, while the beam specimens failed in shear after undergoing significant moment redistribution from hogging to sagging moment region. The moment distribution observed about 21.5% from FEM of beam specimen GN-1.2-0.48-d, while the experimental results achieved 24% at failure load. For high strength concrete presented in beam specimen GH-1.2-0.63-d, the result showed about 20.2% moment distribution, compared to that achieved experimentally of 23% at failure load. In aggressive marine environments or structures persistently exposed to corrosive elements, the deterioration of RC (reinforced concrete) structures is a significant problem, particularly the corrosion of steel reinforcement bars. Recently FRP (Fiber-Reinforced Polymer) composites have been used for strengthening of concrete structures ,2. Also,Several studies confirmed that FRP reinforced continuous beams redistributed moments similar to that in steel-reinforced continuous beams ,7,8. MahStudies investigating the moment redistribution of beams typically use beams that are flexure-critical ,18,19. TThe methodology adopted here in this study is illustrated in the flowchart shown in cE for concrete was calculated using Equations (1) and (2), respectively, while the uni-axial rupture stress, rf, was calculated using Equation (3).f′ is the concrete ultimate compressive strength, and cγ is the concrete density. The stress-strain relationships were calculated by Equations (4)–(6) [f′, and n is a curve-fitting factor. Furthermore, the open and closed shear transfer coefficients were assigned as 0.2 and 0.8. Finally, the Poisson’s ratio of concrete was assigned by 0.2 based on the current literature review [An eight-node solid element, SOLID65, available in the ANSYS  element '+6900)γc001.5(3) (4)–(6) ,25.(4)fe review ,26,27,28A LINK180 element was used to model GFRP reinforcement as discrete elements with shared nodes to simulate the embedded reinforcement within the concrete section. The element has two nodes with three translational degrees of rotation, which presents the GFRP reinforcement embedded into the concrete section. This element is defined by linear-elastic behavior up to failure. Similar to the concrete, the Poisson’s ratio was valued by 0.2 for the GFRP reinforcement. The elements of the GFRP reinforcement were at the exact location as those of the concrete elements. In other words, the LINK180 element, which shows the reinforcement, shares some nodes of SOLID65 that presents the concrete. A three uni-directional nonlinear spring element COMBIN39 was then used to simulate the embedding of the reinforcement within concrete elements in x, y, and z directions. The spring elements in the longitudinal direction, parallel to rebar reinforcement, denoted the reinforcement and concrete bond-slip behavior. The spring elements in the other two transverse directions, perpendicular to longitudinal reinforcement, exemplified the reinforcement’s dowel strength or anchorage reinforcement behavior. The spring force and the corresponding bond slip in the direction parallel to reinforcement were obtained from the bond stress and slip for sand-coated GFRP bars existing in the literature review. Alves et al.  investigMoreover, the anchorage behavior was modelled through the spring perpendicular to the direction of the reinforcement elements using the linear stress–displacement relationship. The stress was limited to the shear strength capacity of the reinforcement, while the corresponding displacement was evaluated by calculating the transverse strain of the reinforcement. The reinforcement’s transverse strain could be obtained by multiplying the longitudinal strain of the reinforcement with Poisson’s ratio. Thus, the corresponding displacement could be determined through transverse strain multiplied by the bar diameter. Although the discussion above regards the used properties for simulating the longitudinal and transverse GFRP reinforcement, the shear strength or dowel strength of bars was not mentioned in the experimental setup . Thus, fTwelve continuous concrete beams reinforced by GFRP bars both longitudinally and transversely were analyzed using nonlinear finite element modeling using ANSYS . The beaThe reinforcement configuration and concrete strength varied according to the parameter in question. Only a quarter of the beam was modeled as the beam specimen was symmetrical in the x and y directions. The first axis of symmetry in the x-direction was at the middle support, separating two identical spans at the middle support, so a single span was only modeled. Moreover, half of the beam cross-section was modeled with a width of 100 mm and an axis of symmetry running in the y-direction. A convergence study was conducted using mesh sizes of 50, 25 and 10 mm. The appropriate mesh size was selected after comparing the deflection values, longitudinal tensile strains, and compressive strains between three identical 50, 25 and 10 mm mesh size models. No significant differences at mid-span deflection, longitudinal tensile strains, and compressive strains were denoted when comparing models established using 25 and 10 mm mesh size. On the contrary, when comparing 50 and 25 mm mesh size models, significant differences at mid-span deflection were observed. Thus, a 25 mm mesh size was selected to reduce the number of elements and the time required for analyzing each beam specimen. The total applied load was applied in a series of increments. At the end of each load increment, the model’s stiffness matrix was updated, taking into account the nonlinear behavior of structure and materials. Newton Raphson equilibrium iterations were used to update the stiffness matrix. The out-of-balance load vector was evaluated, which is the difference between forces corresponding to internal stresses and the applied external load. If the difference was within the tolerance limit, convergence was accomplished, and the load was iteratively further incremented . Becaused and GH-1.2-0.63-d. In this study, the beam specimens included the two main parameters. A finite element model (FEM) was established for verification based on the literature review of Mahmoud . The detd and GH-1.2-0.63-d provided 345 kN and 517 kN values, as Mahmoud [d, and GH-1.2-0.63-d had a mid-span deflection of 15.1 mm and 25.5 mm. While, the FEMs reported 15.2 mm and 22.5 mm, at failure for beam specimens, GN-1.20-0.48-d, and GH-1.2-0.63-d.The experimental and FEM results of the two-beam specimens in mid-span deflection, longitudinal strains at the hogging moment, and the transverse strain of stirrups were compared in  Mahmoud  reportedd, while the experimental results achieved 24% at failure load. For high strength concrete presented in beam specimen GH-1.2-0.63-d, the result showed about 20.2% moment distribution compared to that achieved experimentally of 23% at failure load. Regarding the failure mode of beam specimens, GN-1.2-0.48-d and GH-1.2-0.63-d failed due to diagonal tension cracking at the middle support, according to the reported experimental results by Mahmoud [d failed in diagonal tension after a diagonal crack at interior support intersecting the bent portion of the stirrups, causing brittle failure. On the contrary, the modelled beam specimen GH-1.2-0.63-d failed in web crushing at the middle support. The stirrups at the interior shear region underwent large strains until the diagonal crack extended to the compression zone of the concrete at the top fiber of the beam specimen, then failed by crushing the web. This behavior could attribute to the slight difference between the diagonal cracking angles at interior support for both beam specimens, causing diagonal tension that did not pass through the bent portion zone of the stirrups. Thus, this action allowed the straight portion to resist the more significant loading and straining action at interior stirrups. Furthermore, the two-beam specimens were observed to have a similar moment redistribution. The moment distribution observed about 21.5% from the FEM of beam specimen GN-1.2-0.48- Mahmoud . From thd and GH-1.2-0.63-d, at failure. As shown in d continued until crushing failure at the elements near the interior shear crack. Furthermore, the FEMs provided cracks through every SOLID65 element as these elements cracked in three stages by the order during loading having independent orientation. d with concrete strength of 43 MPa, while d with concrete strength of 80 MPa.d, and GH-1.2-0.63-d, provided a good agreement with the experimental values regarding failure loads, both reinforcement strains , mid-span deflection, and moment distribution. These observations confirmed the reliability of the material properties assigned for modelling the continuous beams reinforced with longitudinal and transverse GFRP rebars using normal and high concrete strength. Thus, with the observations mentioned above, the FEM created could accurately predict the behavior of the continuous concrete beams reinforced with longitudinal and transverse GFRP reinforcement and could be reliably used to conduct a parametric study.The FEMs for the two-beam specimens, GN-1.2-0.48-Based on the CAN/CSA S806  code, thMoreover, the transverse reinforcement effect was investigated through various models for beam specimens in which the spacing of the stirrups was changed from 115 to two-thirds and halved the later spacing. Thus, reducing the shear reinforcement ratio should allow the beam to undergo more deformations after shear cracking at supports before its failure and, hence, more moment redistribution. It should be mentioned that the top and bottom longitudinal reinforcement were equal in bar diameter 15.9 mm and reinforcement ratio of 0.8%. The stirrups diameter was constant at a 6.3 mm value for the beam specimens. The concrete strength of the beam specimens, in this case, was changed from normal to high strength; 40 MPa presents the normal, and 80 MPa represents the high concrete strength. For high concrete strength beam specimens, the spacing of the initial stirrups was 150 mm instead of 115 mm for those of normal concrete strength beam specimens. The beam specimens of normal concrete strength had a compressive strength of 40 MPa, while high strength specimens had 80 MPa.Finally, the effect of the longitudinal reinforcement ratio on normal and high concrete strength concrete beams was investigated. Current FRP design recommendations CSA/S806  obligateDimension, reinforcement details, and test setup for typical beams specimen used here in this study are shown in Consequently, increasing the concrete compressive strength enhanced the cracking load capacity of the beam specimens. Furthermore, increasing the concrete compressive strength resulted in higher load capacity of beam specimens with more significant mid-span deflection until failure. These observations agreed with the findings of El-Mogy et al.  and TaheThe latter behavior could illustrate the reason for those beam specimens of 70 and 80 MPa concrete strength in which no increase in total capacity was observed and, therefore, no moment redistribution occurred, contrary to those beam specimens with lower concrete strength. The results showed that increasing the concrete compressive strength from 50 to 60 MPa resulted in a 14% enhancement in beam capacity. Increasing strength from 60 to 70 and 70 to 80 only resulted in 10% and 7.5% enhancement in the total capacity of the beam specimens, respectively. The average moment redistribution was 13% across the beam specimens. The reduction in stirrups spacing from 115 mm to 57.5 mm resulted in an increase of 8.3% of moment redistribution for the beam specimens. The result showed that normal strength concrete beam specimens exhibited higher moment redistribution than those of high strength concrete counterparts specimens; however, both groups exhibited a redistribution of the moment when reducing the spacing of the stirrups. These findings were in good agreement with those of El-Mogy et al. [The link between the longitudinal reinforcement ratio and the moment redistribution at the middle support is shown in rV, of FRP-reinforced concrete members can be computed as the sum of concrete and stirrup contribution resistance as:The CSA S806  specifievd, was calculated using the depth of the longitudinal reinforcement (from the extreme top fiber of the beam till the centroid of the bar) multiplied by 0.9. The concrete contribution cV for sections with an effective depth not exceeding 300 mm and with no axial load acting on them could be calculated using the following Equations (8)–(10):λ is the concrete density factor and equal to 1.0 for normal density concrete, flE on the shear strength of the section in consideration. The vertical stirrup contribution in a concrete member, vA presents stirrup reinforcement, and The effective depth of cross-section, Vc presents the concrete contribution, wv presents the shear transferred across the crack, and tv shows the vertical FRP stirrups contribution. Finally,For comparison purposes, a literature review of other models was used. Oller et al.  had proptE and tε are the elastic modulus of the stirrup reinforcement and the mean strain in the stirrups, respectively. The mean strain of the stirrups could be obtained as a fraction of the ultimate rupture strain of FRP stirrups, wv, which could be obtained from Equation (18) as follows:The concrete contribution is the function of beam size and depends mainly on the shear span of the beam in meters, as presented by the factor fG simulated the fracture energy of concrete and evaluated it as a function of concrete rupture strength and ultimate tensile strain.The FEM/VPred ratio of 0.76 ± 0.12 and a variance coefficient of 15%.p values of 0.0003 and 0.0005 that were significantly less than the p values of the rest of the parameters.A multivariate linear regression analysis was conducted on the 24 beam specimens in the parametric study using several key parameters that could influence moment redistribution. Parameters with a low statistical significance were discarded to maximize the coefficient of determination. As a result, Equation (19) was formulated: The numerical simulation using the finite element model by ANSYS software adequately predicted the behavior of continuously supported GFRP reinforced beams. The results extracted from the FEMs were in good agreement regarding ultimate failure loads, deflection behavior, and moment redistribution against the experimental data provided by Mahmoud .Despite the absence of plastic behavior in GFRP reinforcement, moment redistribution still occurs on GFRP reinforcement beams at the post cracking stage and the degree of redistribution affected by GFRP reinforcement.d, and GH-1.2-0.63-d were in good agreement with their experimental results. The moment distribution observed about 21.5% from the FEM of beam specimen GN-1.2-0.48-d, while the experimental results achieved 24% at failure load. For high strength concrete presented in beam specimen GH-1.2-0.63-d, the result showed about 20.2% moment distribution as compared to that achieved experimentally of 23% at failure load.At failure, the two FEMs established for simulating beam specimens, GN-1.2-0.48-The increase in concrete strength resulted in an enhancement in moment distribution. The behavior was limited only to beams that had a concrete strength not exceeding 60 MPa. High-strength concrete specimens with concrete strengths more than 75 MPa generally distributed less moment than their normal strength concrete counterparts.The reduction in stirrups spacing from 150 to 75 mm caused an overall increase in moment redistribution by 13.7% at normal concrete strength. The reduction in stirrups spacing from 115 mm to 57.5 mm, resulted in an increase of 8.3% of moment redistribution for the beam specimens at high concrete strength.Stirrup spacing impacted the moment redistribution in continuous beams. However, its ability to influence moment redistribution seemed to diminish with high concrete strengths. In addition, the relationship between spacing and moment redistribution was not directly proportional. Reducing the shear reinforcement ratio by reducing the stirrups’ spacing while maintaining constant stirrup diameter did not always enhance moment redistribution.Limited to this study, the CSA S806  had a meThis study has shown that the GFRP reinforcement can be effectively modelled in ANSYS software. The finite element analysis results were found to be in close agreement with the experimental results. The finite element analysis is always considered a more affordable and faster analysis approach as compared to the labor-intensive investigations . Therefore, the outcome of this study is very useful, and the proposed analysis can be further used for the economical and safe design of GFRP reinforced concrete structures.The numerical investigation was initiated by creating an FEM to simulate the behavior of continuously supported concrete beams reinforced with longitudinal and transversal GFRP bars reinforcement. The FEM was verified against the experimental results shown by Mahmoud . A param


Multiple studies have shown that antibiotic utilization increased during the COVID-19 pandemic. However, the impact of this increased utilization has not been well established. The aim of this study is to describe the trends in minimum inhibitory concentrations for various antibiotics against common gram-negative pathogens observed since the start of the COVID-19 pandemic as compared to previous years.This retrospective study was conducted at the Memphis VA. All respiratory, urine, and blood culture MicroScan results run from October 2017-March 2021 were analyzed. Only inpatient and emergency department data was included. The MIC50 and MIC90 of seven antibiotics for four of the most common pathogens were trended by quarterly intervals.Pseudomonas aeruginosa was noted to have the most sustained increase in MIC90 across various antibiotics. In the last 3 quarters of the study time frame, piperacillin-tazobactam mean MIC90 increased from 32 to 64, cefepime from 8 to > 16, and meropenem from 4 to > 8. Escherichia coli had a sustained increase in ceftriaxone MIC90 from < 1 to > 8 in the final quarter of 2020 and beginning of 2021. Klebsiella pneumonia was also found to have a sustained increase in cefepime mean MIC90 from < 1 to > 16 during the year of 2020, with return to previous MIC90 the following quarters.MIC50 and MIC90 were compared using standardized breakpoints. As compared to previous years, Previous studies have clearly demonstrated a widespread increase in antibiotic utilization during the COVID era. Our study demonstrates how even short-term increases in antibiotic use can lead to shifts in MIC, if not outright resistance. This was demonstrated across multiple common gram-negative pathogens and to various broad-spectrum antibiotics which were commonly used more frequently during COVID-19. Further analysis will be needed to determine whether these trends continue or whether the decrease in antibiotic utilization in the recent months will lead to similar decrease in MIC.All Authors: No reported disclosures


The by-product of the foundry industry is waste foundry sand (WFS). The use of WFS in building materials will safeguard the ecosystem and environmental assets while also durable construction. The use of industrial waste in concrete offsets a shortage of environmental sources, solves the waste dumping trouble and provides another method of protecting the environment. Several researchers have investigated the suitability of WFS in concrete production instead of natural river sand in the last few decades to discover a way out of the trouble of WFS in the foundry region and accomplish its recycling in concrete production. However, a lack of knowledge about the progress of WFS in concrete production is observed and compressive review is required. The current paper examines several properties, such as the physical and chemical composition of WFS, fresh properties, mechanical and durability performance of concrete with partially substituting WFS. The findings from various studies show that replacing WFS up to 30% enhanced the durability and mechanical strength of concrete to some extent, but at the same time reduced the workability of fresh concrete as the replacement level of WFS increased. In addition, this review recommended pozzolanic material or fibre reinforcement in combination with WFS for future research. Concrete is a commonly used building raw material on the planet, and it serves as the foundation for all construction and development projects . To varyFine aggregate (sand) is one of the essential components in producing mortar and concrete, and it plays a critical role in the design mix . Sand isZirconium oxide is a white crystalline oxide of zirconium, with a monoclinic crystalline structure, is the mineral baddeleyite. Zirconia materials have been considered limited in their use due to their poor bonding strength to different types of cement. To enable a good mechanical bond to be established, it is necessary to have a rough surface. This is a common technique for silica-containing glass ceramics that uses hydrofluoric acid as an etching agent. However, zirconia ceramics are not reported to benefit from this method because it does not produce a surface rough enough to improve adhesion between cement and zirconia ceramics .Chromite-rich sand is a source of chromite, a mineral, from which chromium metal is obtained. Chromium is primarily used as a coating on metal—termed chrome—deposited electrochemically, to protect it from rust and for decorative purposes. Different studies focus to used chromium sand in cement concrete production. According to research, A small amount of chromium has been introduced into the cement paste to accelerate hydration . In a stWaste production has increased as a result of rising population and technological advancements. As a result, numerous scholars and researchers around the globe are working to find innovative approaches to decrease this waste or, as a clearer option turn them into valuable reserves ,11,12,13In foundry processes, foundry sand refers to clean, uniformly sized, high quality silica sand that is used in the casting process. Sand is bonded to form molds or patterns which are used to make ferrous (iron), non-ferrous  metal castings. Components with easy or complicated structures can be created from several matters that can be molded in a single step. The foundry industry is one in which different iron, leftover steel, and ferroalloys are molten in kilns or cupolas, made in sand, ceramic, or metal molds, and produced steel, nodular, and hardened foundry goods are manufactured as raw or processed materials . WFS is 6 tons of foundry sand are used in production each year; about four to seven million tons are wasted each year and offered for recycling [The two categories of foundry sand accessible are clay-bonded (Greensand) and chemically bonded sand. Greensand is perhaps the most widely used moulding medium, consisting of the aggregate, bonded with a mixture of mainly clay and water which as Chemically Bonded sand moulds are created using a wood, metal, or plastic pattern. Steel casting foundries in the United States unload roughly nine million tons of expended sand into garbage dumps every year . Foundryecycling . The fasecycling . Sand beecycling . Currentecycling . In the ecycling .One of the major issues faced by foundries is the accumulative capacity and management of the stockpiled WFS as it requires a large space for accumulation. There is a risk associated with stockpiled waste foundry sand due to the high rate of toxic metal leaching from the waste foundry sand, which results in WFS posing a threat to the sustainability of the environment . Hence, 3) which is equal to the natural sand (1600 kg.m3). The existence of binders and additives was found to cause reported values of WFS absorption to vary greatly but are usually on the greater end of normal sand. Numerous foundries even use binders, such as clay, sawdust, and wood for molding. The existence of these elements lowers the material’s specific density while also lowering the density of the concrete by making air voids. The percentage of particles smaller than 75 microns is 18 to 24 percent. The physical properties of industrial wastes, including grain size distribution, density, specific gravity, fine substance, and absorption, assist in determining their applicability and ability to utilize fine aggregate in concrete. WFS is usually semi-circular or circular in shape. It has a consistent grain size distribution, with 85–95% of it having grains between 0.6 and 0.15 mm and 5–12% having grains smaller than 0.075 mm . Figure 2 is significantly abundant. In comparison to SiO2, the ratios of the other components are extremely low. The chemical composition of WFS varies depending on the kind of metal, binder, and combustible applied, and this impacts its operation. In sands from a single foundry, on the other hand, the properties of WFS do not show the difference with time. Additionally, Blended sands manufactured by foundry consortiums commonly generate sands with the same constituents. WFS has a high silica content and resins/chemicals, bentonite, sea coal and dust [According to previous research, the chemical composition of WFS is displayed in and dust . A studyand dust  the chemand dust .Concrete workability measures the ease in which fresh concrete could be placed, consolidated, and finished to minimum losses of uniformity. Any concrete mixture should be feasible enough to be adequately placed and consolidated and fill the forms and surround the reinforcement or other embedded items. The workability and strength of concrete are directly related to each other. The strength of concrete increases as the flowability of normal concrete increases, affecting the concrete’s durability. Workability impacts placement and finishing operations’ capacity, performance, appearance, and sometimes even labour costs. When it comes to optimum concrete design, there are a variety of expectations and agendas among the design/construction team. The structural engineer desires increased strength as well as a strong bond with reinforcing steel. The architect is involved regarding esthetics. Load-carrying capacity is valuable to the holder since it allows for relatively small cross-sections of structural members hence more serviceable floor space. A labourer demands concrete mix that can flow, place, and compact quickly and easily, while a finisher wants something that can be durable and gives better finishing. A concrete blend along with excellent flowability balances several characteristics, resulting in a high-quality product with long service life. Concrete compaction is reduced, and porosity is increased due to poor concrete workability. The concrete density decreases as porosity increases, resulting in lower compressive strength. One of the most critical aspects to consider is your ability to work.The compacting factor analysis is performed mainly for experimental needs, but it can also be used in the field. It is more precise and sensitive than the slump test, and it is particularly suitable for low flowability concrete mixes. It’s also frequently used when concrete is compacted with a vibrator. Bilal et al.  found thConcrete’s compressive strength is its ability to resist compressive loads before actually failing. The compression test seems to be the most essential of several concrete assessments since it gives information about the concrete’s characteristics. The concrete compression strength after 28 days curing, as ascertained by different researchers, in which fine aggregate is full or partial substitute with WFS, is displayed in 2 present in WFS with calcium hydrate (CH) formed during the hydration of cement. CSH improves the binding aspects of concrete leading to more strength. The decrease in compressive strength was observed with further than 30% substitution of WFS. With further than a 30 percent substitution, a decrease in strength was noted. This noticeable drop in strength properties with the addition of 40% WFS might be credited to an increase in the surface area of fine particles of WFS, resulting in a reduction of the water-cement gel in the matrix. As a result, the coarse and fine aggregate binding process is flawed [s flawed . The ress flawed ,57. In cs flawed  used WFSs flawed . For sigs flawed ,59.Concrete’s tensile strength is one of its fundamental and most significant characteristics which influences the amount and range of cracks that occur in a structure. Furthermore, the concrete is weak in tension owing to its brittle nature, which makes it prone to cracks. This means that it will not be able to withstand direct tension. Accordingly, cracks develop when tensile forces go beyond the tensile strength of concrete. As a consequence, it is required to ascertain the tensile capacity of concrete to detect the limit of load at which the concrete can crack. Additionally, the splitting tensile strength test on a concrete cylinder is a method that can be used to determine the tensile capacity of concrete. It is carried out in accordance with ASTM C496 .The tensile strength of concrete can be indirectly measured by its flexural strength. The maximum tension is applied to the tension face of an unreinforced concrete beam or slab at the point of failure during bending testing. The strength of concrete is determined by loading 150 × 150 mm (or 100 × 100 mm) concrete beams with a span length greater than three times the depth. Flexural strengths are expressed as Modulus of Rupture (MR) in MPa and are calculated by standard tests ASTM C78 . Figure Concrete can be described as durable if it can withstand weathering action, chemical attack, abrasion and any other deterioration process. In adverse environments, durable concrete must maintain its original form and serviceability. The durability of concrete can be detected through various tests, such as water absorption, density, acid attacks, dry shrinkage, ultra-sonic pulse velocity, etc.An assessment of concrete durability (water absorption) is an indirect measure of concrete porosity that is an indirect measurement of concrete durability. The water absorption capacity and the porosity of hardened concrete play important roles in its durability. To further increase the flexural and compressive strength and durability of concrete, it is important to reduce its porosity . Figure Conventional concrete without waste foundry sand (WFS) results in the least amount of water consumption and there is a significant increase in water absorption rate when the rate of replacing WFS is increasing . AdditioAn acid attack occurs when acid-susceptible constituents, such as calcium hydroxide and hydrogen peroxide are dissolving and leaching from the cement paste of hardened concrete. As a consequence of this action, there is an increase in capillary porosity, a decrease in cohesiveness, and ultimately reduced strength. Cracking and disintegration may occur as the result of an acid attack, particularly when the structure is exposed to water pressure on one side.2SO4, concrete with WFS shows less corrosion compared to the reference concrete [concrete . HoweverIt is well known that concrete’s mechanical properties are greatly influenced by the density of the concrete. In general, dense concrete provides higher strength and less porosity and voids.Concrete carbonation is one of the major factors associated with the corrosion of steel reinforcements in concrete structures. A general rise in carbon depth was observed as the replacement level of WFS increased.3A is created in the binder, resulting in greater resistance to corrosion. The WFS used in this study contains 4.93 percent Al2O3, which is similar to cement. Even though Al2O3 and SiO2 can be found in the WFS to create the densified tri-calcium aluminates (C3A), the low workability of the concrete causes difficulty in the compaction process, leading to the formation of a continuous permeable microstructure. There is an additional possibility that, as a result of the WFS grains being present in the concrete, air pockets were created in the concrete. A crack or an opening in the concrete may have allowed the water to penetrate. It was because of the creation of this continuous pore system that chloride ions were able to penetrate. It appears that blends of WFS 40 percent and WFS 50 percent have a considerably greater chloride penetration compared to the control mix. Generally, the replacement of the WFS in concrete has a deep effect on the penetration of chloride. Although, this effect was not critical up to a replacement ratio of 30, the penetration value was generally accepted as being much lower at both ages of concrete. Ahmad et al.  stated tThis paper examined the utilization of WFS as a fine aggregate in concrete production. In this review, all the essential properties, such as the physical and chemical composition of WFS, fresh properties, mechanical and durability performance of concrete have been discussed and compared. Even though WFS has a few harmful impacts on concrete performance when utilized in a higher or full substitution instead of natural sand in concrete production; it can be utilized in concrete production up to a certain extent. Several investigations have been conducted regarding the use of WFS in concrete. The optimum substitution dose is determined to be 30% concerning most of the properties tested. Furthermore, a detailed conclusion is listed below.There was almost no difference in bulk density, specific gravity, or grain size distribution between WFS and natural sand.Flowability of concrete reduced with the substitution of WFS. This is owing to the physical properties of WFS (porous and larger surface area) which increased water demand. However, up to 30% substitution of WFS shows acceptable workability but a higher dose (beyond 50%) needed a higher dose of admixture (plasticizer).WFS can be used up to 30% substitution instead of natural river sand with no harmful influence on concrete strength. This is owing to the micro filling which provides more dense concrete, leading to more resistance to load. However, a decrease in strength was observed at a higher dose of WFS (beyond 50%). The reason for the decrease in strength is the lack of workability that increases the difficulty in the compaction process, which results in more voids in the hardened concrete.Adding WFS tends to decrease its mechanical strength. The lack of workability caused pores to develop in concrete and less paste to be available for binding, resulting in reduced strength. Results can be comparable to the control concrete at a 20% replacement level of WFS. A 30% replacement of WFS has been suggested in some studies.Improvement in durability aspects  of concrete with WFS was observed. This is due to the dense matrix due to the addition of fine WFS.Finally, this overall review concluded that WFS up 20 to 30% can be used as fine aggregate in concrete production without any negative effect on the mechanical and durability performance of concrete. Furthermore, less information is available on the durability performance of concrete with WFS. Therefore, this review strongly recommended a detailed study on the durability performance of concrete with partially substituted WFS. Additionally, up to 30% substitution of WFS shows the mechanical performance of the concrete is approximate to the control concrete. Further study was recommended to add fibers or some of the pozzolanic materials, such as fly ash or silica fume to improve the mechanical performance.


Background: Antibiotic-loaded spacers are often used during two-stageexchange for periprosthetic joint infections (PJIs) both for its mechanicalproperties and as a means of local antibiotic delivery. Purpose: The main goal of this study is to compare the efficacy of differentoptions of antibiotic(s) in spacers concerning the rate of positive culturesat the second stage. Patients and Methods: We retrospectively evaluated two-stage exchangeprocedures for infected hip or knee arthroplasty performed between 2012 and 2018 inwhich adequate (at least four deep tissue samples) culture results in bothstages were available. The type of spacer and antibiotics used, inaddition to several other patient, infection and treatment-related variables,were registered and correlated to microbiological findings in the secondstage. Results: Fifty-eight cases were included with a 19.0 % (11/58) overall rateof positive cultures during reimplantation. With a mean follow-up of 46months, failure rate was significantly higher at 63.6 % (7/11) in caseswith positive cultures at reimplantation compared to 4.3 % (2/47) for thosewith negative cultures during reimplantation (Conclusions: Results show that combined antibiotic therapy spacers areadvantageous when compared to gentamicin monotherapy as they producesignificantly lower rates of subsequent positive cultures during the secondstage. Hand-mixed high-dose vancomycin/meropenem spacers seem to performjust as well as prefabricated commercially availablevancomycin/gentamicin options.Level of Evidence: Therapeutic level III. It is indisputably a source of significant deleterious impacton a patient's health status and quality of life. As the requirements fortotal joint arthroplasty have been increasing and are expected to continue to steadilyincrease so will the burden of infection .PJI treatment options are greatly limited by the presence of bacterialbiofilm on the prosthesis' surface. These are highly structured communitiesof microbial cells surrounded by an extracellular matrix that protects themagainst the host's immune system action and virtually everyantibiotic . Once a mature biofilm is established,removing the implant is the only sensible alternative to eradicate theinfection. As such, exchange revision surgery is widely considered to be thegold standard treatment for PJI.Although one-stage exchange is gaining momentum worldwide, it is mostly usedin selected cases, and two-stage revision surgery is still the most commonalternative . When a two-stage strategy ispreferred, most surgeons agree on the use of antibiotic-loaded cementspacers with two main objectives in mind: local antibiotic delivery andpreservation of joint stability and function between stages that offers somecomfort to the patient and prevents soft-tissue contractures. Ultimately,they contribute to an easier and faster second-stage reimplantationsurgery .Several different spacer options exist. They can be static or mobile andprefabricated or handmade, and a number of different antibiotics can beincorporated. Despite the large amount of research on this topic, severalcontroversies persist, and it is not clear which (if any) is the best choice.The main goal of this paper is to, based on the rate of positive cultures atthe second stage, compare the efficacy of single vs. combined antibiotics in eradicating PJI. A secondary goal is to ascertain a possible performancedifference between prefabricated and handmade spacers.2Staphylococcus aureus, Gram-negative rods, Enterococcus species and fungi were furtherclassified as difficult-to-treat microorganisms.We retrospectively evaluated all two-stage exchange procedures performed atour university hospital for infected hip or knee arthroplasty between 2012 and2018. Basic patient demographics and comorbidities were registered, as well as infection-related clinical variables such as type of implant (primary or revisionprosthesis), whether there were previous surgeries for infection, andmicrobiological findings in the first and second stages.Methicillin-resistant Treatment-related information such as duration of first-stage surgery, thetype  and antibiotic(s) used in thespacer, time interval between stages, duration of systemic antibiotictherapy and whether the patient was operated on by a dedicated septic team werealso thoroughly collected. Cases in which no cultures were obtained duringreimplantation and cases without sufficient data on antibiotic(s) used incement spacers were excluded.2.1Staphylococcus aureus, Gram-negative rods,Enterococcus species, Streptococcus species or Candida species) or (ii) at least two of the low-virulence microorganisms with the same antibiogram were isolated.Definitive diagnosis of PJI during the first stage was based on thediagnostic criteria proposed back in 2011 by the Musculoskeletal InfectionSociety  and further refined in2013 . Given the lack of accuracy ofaforementioned criteria to identify persistent infection at the secondstage , a different criterion was adopted.Reimplantation cultures were considered significant when (i) at least one ofthe virulent microorganisms was isolated  after deep tissue sampling(favouring the bone-implant interface) and prosthesis removal forsonication. The choice of which specific type of spacer to use was at thesurgeon's personal discretion based on availability and specificconsiderations in each case.Systemic antibiotic therapy was prescribed based on antibiotic sensitivityprofile of isolated microorganisms. The timing of reimplantation was decidedby treating physicians and was mostly based on trending serum inflammatoryparameters and clinical impression in each case.Second-stage surgery is routinely performed under cefazolin prophylaxis,followed by a broad-spectrum antibiotic regimen despite initial microbiologyresults that are continued until intraoperative culture results. At leastfour tissue samples (or three tissue samples and sonication of the removedimplant and/or spacer) were required to classify them as adequate sampling ineither the first or the second stage.All patients who had positive cultures at reimplantation were subsequentlytreated with appropriate antibiotics for an additional 12 to 24 weeks.2.3IBM SPSS Statistics 24 was used for the statistical analysis. The groupswere compared using the Student's 3Medical charts of 81 two-stage exchange total hip arthroplasty (THA) or total knee arthroplasty (TKA) cases were reviewed. Thirteen cases were excluded because ofinadequate cultures obtained during second-stage surgery, and 10 cases wereexcluded due to a lack of reliable information on the antibiotic(s) usedin the cement spacer. Demographic and clinical information of the 58patients ultimately included in the final analysis are shown in Table 1.The majority of cases had undergone previous surgical treatment for PJI,mostly failed previous debridement and implant retention but also failedprevious two-stage exchange.Concerning type of spacer, prefabricated commercially available gentamicin-loaded spacers were applied in 14 cases (24.1 %), and gentamicin- andvancomycin-loaded spacers were used in 24 cases (41.4 %). Hand-mixed high-dose vancomycin (3 g) plus meropenem (2 g) per 40 g of low-dose gentamicin (0.5 g)polymethyl methacrylate (PMMA) manufactured spacers were used in 20 cases(34.5 %). Dual antibiotic therapy spacers were less often used in THA thanTKA (54.5 % [12/22] vs. 88.9 % [32/36]), Staphylococcus aureus, two includingEnterococcus species, six cases involving Gram-negative rods, one fungi caseand three polymicrobial infections including any of the previous bacteria.Microbiological findings in the first stage are summarized in Table 2. PJIcases during the first stage categorized as difficult-to-treat microorganism includedthree cases of methicillin-resistant There was significant growth in cultures taken during the second stage in11 (19.0 %) cases. Failure rate after reimplantation was 15.5 % (9/58)with a mean follow-up of 46 months (interquartile range 24–48 months) afterthe second stage. It was significantly higher in those patients who hadpositive cultures during the second stage (63.6 % [7/11]) compared tothose with negative cultures (4.3 % [2/47]). Despite the fact that allpositive cases were subsequently treated with systemic antibiotics for aperiod of 12 to 24 weeks .Further analysis exploring combined antibiotic therapy spacers found nostatistically significant difference between the gentamicin- and vancomycin-loaded prefabricated commercially available spacers and the high-dosevancomycin and meropenem hand-mixed manufactured spacers  ofmicroorganisms isolated during second-stage cultures were some kind ofpersistent microorganism already present in the first stage (Table 5). Asmentioned above, systemic antibiotic therapy after first stage wasprescribed based on antibiotic sensitivity profile of isolatedmicroorganism, and was never less than 6 weeks. Timing of reimplantation wasdecided by treating physician(s) and was mostly based on trending seruminflammatory parameters and clinical impression in each case.When the microorganisms isolated in the first stage are resistant toantibiotics in the spacer, the risk of positive cultures on reimplantationis significantly higher despite appropriate systemic antibiotic therapybetween stages  treatment is complex and laborious.Although several controversies still exist, there is a consensus thatchronic infections, with established and mature biofilm, require completeexchange of the implant. Currently, the most popular strategy is still toperform one initial surgery to accomplish exhaustive surgical debridementand complete implant removal followed by a second surgery in a few weeks toreimplant a new prosthesis after the infection is deemed to be cured, i.e. atwo-stage exchange. When this two-stage strategy is preferred, the goal ofthe interim period between surgeries is to eradicate infection whileoptimizing local conditions for a successful revision surgery.A major potential advantage of the use of spacers is the possibility oflocal antibiotic therapy. The local antibiotic delivery theoretical advantage isthat it can result in very high drugs concentration at the site ofinfection with low serum levels, thus reducing its potentialtoxicity .Although some authors advocate that the choice of antibiotics needs to beindividualized for each case based on the pathogen antibioticsusceptibility, often there is no pathogen identified preoperatively, and inaddition it has been shown that a significant proportion of cases will showdisagreement between pre- and intra-operative microbiologicalfindings .As such, our approach has been to adopt broad-spectrum antibiotics inspacers. Traditionally, available commercial spacers are impregnated withgentamicin which has a good activity against a wide range of Gram-positiveand Gram-negative bacteria. However, the high prevalence of gentamicinresistance especially among coagulase-negative staphylococci fuelled oursearch for an alternative . Given thecharacteristics of PJI bacterial flora in our institution , we decided that we would like to have broad Gram-positive coverage,and that led us to adopt the use of surgeon hand-mixed cement spacersincorporating vancomycin. Aminoglycosides for Gram-negative coverage wouldbe a natural association with vancomycin but a lack of available powderformulation for cement mixing in our pharmacy led us to the search of anadequate alternative, and meropenem was ultimately chosen . Our policy over the last few years has been to hand mix 3 g ofvancomycin and 2 g of meropenem for each 40 g of gentamicin-loaded PMMA both forknee and hip spacers. More recently, commercial prefabricated spacerscontaining both vancomycin and gentamicin have become available and werealso incorporated into our clinical practice, especially when long-stem hipspacers are required. This has created a “natural experiment” setting toevaluate the performance of these different spacers.During the second-stage surgery, a new debridement is performed, and multipledeep tissue samples are routinely sent for microbiology. We believe that usingthese results is an adequate endpoint to assess antibiotic therapyeffectiveness, specifically spacer antibiotics. It has been shown thatpositive cultures correlate with increased risk of reinfection, and a directcorrelation seems to exist between higher bacterial load and subsequent riskof failure . Current results confirm a much higher riskof subsequent failure when second-stage cultures show significant growth.With this outcome in mind, our results show the most important prognosticfactor to be the use of combined  antibiotic therapyspacers. The use of gentamicin monotherapy spacers is independentlyassociated with much higher risk of positive cultures in the second stage.Although others have suggested positive cultures in the second stage aremostly caused by microorganisms other than the ones isolated during thefirst stage , this wasnot the case in our study where the majority of positive cultures in thesecond stage revealed some kind of persistent microorganism already presentin the first stage. Naturally, it is more common to encountergentamicin-resistant microorganisms that persist than to encounterinfections with microorganisms resistant to both vancomycin and gentamicinor meropenem. Despite the large number of variables that may influence thisoutcome , the fact that this effect persisted after multivariableanalysis suggests it is a truly independent prognostic factor.Our secondary goal was to ascertain a possible performance differencebetween prefabricated and handmade spacers. Surgeon-made spacers bymanually adding and mixing antibiotics are often criticized not for theirmechanical or functional properties but rather for their erratic andunpredictable antibiotic release kinetics and subsequent clinical outcome.Nevertheless it has been shown in vitro that high-dose manual addition (Several limitations can be pointed to in the current study. Although systemicantibiotic therapy was decided in each case after knowing antibioticsusceptibilities of the infecting pathogens, there was a myriad ofdifferent options, and it was not possible to further explore the influenceof each regimen in the outcome. In any case, local antibiotic therapy withinthe spacer seems to be a more important feature than systemic antibiotictherapy. Also, the retrospective nature of this study and its limited samplesize did not allow for stratification of results per type of microorganism,but we did find that the presence of classically difficult-to-treatmicroorganism does not seem to be a significant factor if they are sensitiveto the antibiotics used in the spacer. Although microorganism species andantibiotic susceptibility profile were used to judge the bacteria found inthe second stage and judge it as persistent or new, we did not performgenome analysis, and this is but a crude assumption. It is not impossiblethat some of them are new infections rather than persistent ones.All facts considered, combined antibiotic therapy spacers seem to be abetter alternative in treating periprosthetic joint infections as theyresult in significantly lower rates of positive cultures taken in the second-stage surgery and lower risk of subsequent failure. Both prefabricatedcommercially available and surgeon-made antibiotic hand-mixed spacersseem to be valid options as there was no significant performance differencebetween them.