ventriculostomy catheters , also known as external ventricular drains ( evds ) , are frequently used in neurosurgery to monitor and relief intracranial pressure . complications arising from evds include hemorrhage , misplacement , dislodgement , blockage , and , most significantly , infection , which may be complicated by ventriculitis , meningitis , brain abscess , or subdural empyema . evd - related infections significantly prolong hospital stay , increase costs , and often negatively affect the overall prognosis . reported rates of evd - related infections range from < 5% up to 23% , most commonly close to 10% . an increased risk of infection has been observed in patients with subarachnoid or intraventricular hemorrhage , in patients with concurrent systemic infections as well as with longer duration of catheterization , cerebrospinal ( csf ) leakage , and frequent manipulation of the evd system [ 24 ] . in addition we hypothesized that multibed accommodation of patients with evd in a mixed surgical intensive care setting may constitute a risk factor for evd - related infections . the objective of the present study was to assess the incidence and outcome of evd - related infections and to identify new and confirm already known risk factors . for this single - center retrospective study we included all patients over 18 years of age that underwent evd placement during a 30-month period ( january 2010 to june 2012 ) at our 1.500 bed tertiary center ( jena university hospital , germany ) . for drainage conventional ( promedics ) and silver - impregnated catheter ( ventriguard ) were used . all catheters were inserted under sterile conditions in the operating theatre using a tunneled procedure technique and a closed system for drainage . there was no policy of routine csf sampling or replacement of catheters during the whole study period . the third - generation cephalosporin ceftriaxone was given at 2  g once daily to all patients from insertion until evd removal . patients that were not immediately transferred to the icu after evd insertion ( n = 5 ) , patients presenting with open skull fracture and csf leakage ( n = 4 ) , and patients with active infection of the central nervous system ( cns ) at first evd implantation ( n = 18 ) were excluded from the study . the 26-bed icu is a mixed icu treating patients of all surgical disciplines in four single - bed rooms , seven two - bed , and two four - bed rooms . the charts of all patients were retrospectively reviewed and demographics , asa - score ( physical status classification of preoperative patients for anaesthetic risk assessment from the american society of anaesthesiologists ) , evd - related data , type of accommodation , and underlying or arising healthcare - associated infections during ventricular drainage were documented . we defined evd - related infection as ( 1 ) positive csf culture result plus clinical symptoms or cns pleocytosis / cell count increase , or ( 2 ) in the case of negative csf culture , clinical symptoms , and cns pleocytosis / cell count increase [ 5 , 6 ] . continuous values were expressed as median ( range ) and compared using the mann - whitney u test . categorical data were presented as frequencies and percentages and compared using the chi - square test or fisher 's exact test where appropriate . cox regression analysis and the kaplan - maier method were used to determine predictors of evd - related infection . on the basis of poisson distribution and wilson - score method , external drainage was continued in median for 7 days ( range 144 ) resulting in 1.725 catheter days ( table 1 ) . the first and second evd remained each in place for a median of 6 days ( 1st : range 119 days , 2nd : range 117 days ) , the third evd for 12 days ( range 916 ) . one patient required a fourth and fifth evd which remained in situ for 11 and 12 days , respectively . indications for extraventricular drainage were nontraumatic subarachnoid and/or intraventricular hemorrhage in 133 ( 61% ) patients , traumatic brain injury with subarachnoid and/or intraventricular hemorrhage in 38 ( 17% ) patients , intracranial tumors in 25 ( 12% ) patients ( n = 8 benign ; n = 17 malignant ) , and others in 22 ( 10% ) patients ( n = 16 contusion / edema ; n = 6 hydrocephalus ) . eighteen patients developed an evd - related infection resulting in a cumulative incidence of 8.3% ( 95% ci , 5.312.7 ) . all patients experienced only one episode of infection . in 14 patients the first evd was infected , in four patients the second one . six patients with an infection of the first evd received a second evd , one of those a third , and one patient five evds in total . reasons for a change were the underlying infection and/or clogging with still necessity of ventricular drainage . thirteen patients without an evd - related infection received a second evd ; the reasons were displacement or clogging . the device - associated infection rate was 10.4 per 1.000 ( 95% ci , 6.216.5 ) evd days considering the total time of evds in place ( 1.725 days ) and 11.8 per 1000 ( 95% ci , 6.918.6 ) evd days considering catheter days without a previous evd - related infection ( 1.572 days ) . on average an evd - related infection became in mean seven evd - related infections were diagnosed within three days after evd placement ( figure 1 ) . in 88 evd procedures a conventional catheter was used and in 122 procedures a silver - impregnated catheter was inserted . in 26 procedures the type of the used catheter was not documented . no significant difference of evd - related infection rate was found between patients with conventional evd or silver - impregnated evd ( 2% versus 9% ; p = 0.08 ) . of 18 evd infections , 16 ( 89% ) the pathogens most commonly identified were coagulase - negative staphylococcus ( cns ) ( 62% ) followed by enterococcus spp . ( 19% ) and other pathogens ( 19% ) including klebsiella pneumoniae , escherichia coli , and micrococcus luteus ( table 2 ) . no association of evd - related infections with demographical parameters , indication for evd placement , and the type of accommodation could be detected ( table 3 ) . furthermore , there was no difference in mortality ( single - bed 14% versus multibed 18% , p = 1.0 ) or in the occurrence of healthcare - associated infections other than evd - related infection between patients accommodated in single - bed rooms and multiple - bed rooms , respectively ( 21% versus 25% , p = 1.0 ) . concomitant healthcare - associated infections ( hais ) were found significantly more often in patients with evd - related infections ( 44% versus 23% , p < 0.01 ) , with a trend towards more surgical site infections ( ssi ) , urinary tract infections ( uti ) , and central line - associated bloodstream infections ( clabsi ) in patients with evd - related infections . no coherence between the organisms responsible for hais and those responsible for the evd - related infection was found . patients with an evd - related infection had a significantly longer icu ( 11 versus 21 days , p < 0.01 ) and hospital stay ( 20 versus 28.5 days , p < 0.01 ) than patients without . median total duration of external drainage was twice as long in patients with evd - related infection ( 6 versus 12 days , p < 0.01 ) . however , there was no significant difference in the duration between first evd placement and the occurrence of evd - related infection , respectively , evd removal in patients without evd - related infection ( 6 versus 7 days , p = 0.87 ) . when controlled for the duration of the infection - free evd drainage as a continuous variable , the occurrence of any hai remained a statistically significant risk factor for the development of an evd - related infection in a multivariate logistic regression model ( univariate or 4.3 , 95% ci 1.611.6 ; adjusted or 7.1 , 95% ci 2.222.9 ) , whereas the duration of drainage until infection or removal was not . cox regression analysis did not identify a significant association between any further studied parameter and evd - related infection . a change of an evd before infection or removal of the evd was also not associated with an increased risk for a subsequent evd - related infection ( p = 0,47 ) . evd - related infection was not associated with increased in - hospital mortality ( 17% versus 18% ; p = 1.0 ) the only parameter associated with adverse outcome was asa - score classification with an odds ratio of 2.7 per 1-class increase ( p < 0.01 ) . the cumulative incidence of evd - related infection in our study was 8.3% and hence comparable with previous published studies [ 13 ] . the device - associated infection rate observed in this study ( 10.4 per 1000 evd - days ) is higher than the rate reported by scheithauer et al . ( 6.3 per 1000 device days ) , which has been the only device - associated infection rate reported until now . noticeably , the mean duration of drainage time in patients without evd - related infection in that study was considerably longer compared to our cohort ( 11 versus 8 days ) . the majority of published series reported a statistically significant higher incidence of evd - related infections in patients with subarachnoid and/or intraventricular hemorrhage when compared with patients with nonhemorrhagic pathologies [ 1 , 4 ] . according to two previous studies [ 6 , 7 ] we however could not confirm subarachnoid and/or intraventricular hemorrhage as an independent risk factor for evd - related infection in logistic regression analysis . several studies examined the relationship between concurrent systemic infections and evd - related infection , showing that concurrent systemic infections are a risk factor for evd - related infection . these results could not be confirmed in our study , in which the presence of a healthcare - associated infection during external ventricular drainage was not a risk factor for evd - related infection . however , patients with an evd - associated infection had significantly more often concurrent healthcare - associated infections , which might be a consequence of the prolonged length of stay in the intensive care unit . as in previous studies there was no coherence between the organism responsible for the healthcare - associated infection and the organism responsible for the evd - related infection in the individual patient . multiple studies examined the duration of catheterization as a risk factor for evd - related infection . interpretation of these studies is complicated because some investigators used cumulative infection rates , either uncorrected or censored by the use of life - table analysis , while others used daily infection rates . even though there is some controversy regarding the actual daily infection rate , lozier et al . could show that the hazard rate varies over time , suggesting daily changing infection risks . although the median total duration of external drainage was twice as long in patients with evd - related infection than in patients without infection , there was no difference between insertion of the first evd and occurrence of evd - related infection or evd removal in patients without evd - related infection . this underlines the fact that prolongation of total drainage time in patients with evd infection is a result of evd infection and not vice versa . in line with these findings seven evd - related infections were diagnosed within three days after placement of the infected evd . four of the seven evd - related early infections were caused by coagulase - negative staphylococci ( cns ) which may have arisen from initial inoculations , which develop in detectable infections after variable incubation periods of around five days as previously suggested . this emphasizes the necessity of evd placement under fastidious aseptic conditions . in accordance with previous studies , coagulase - negative staphylococci were the bacteria most commonly isolated in patients with evd - related infections accounting for 62% of cases . other common organisms include enterococcus spp . , enterobacter spp . , and staphylococcus aureus . this pattern coincides with that of the usual skin flora and hospital environment . concerning our additional research question , whether multibed accommodation of patients in the icu setting poses a risk factor for evd - related infections we were not able to show any difference in the infection rate between patients who were placed in single- or multibed rooms , respectively . the current notion is that evd - related infections result from either inoculation of pathogens during evd placement and/or contamination and colonization of the evd system during the postoperative period . postoperative colonization can either arise from endogenous organisms present on the skin , which spread along the intracutaneous tract or by exogenous organisms introduced into the evd system during manipulation at the evd system by healthcare workers . endogenous infections might be prevented by using antimicrobial coated evd catheters which may decrease bacterial colonization and thus prevent infection . performed a meta - analysis to assess the efficacy of antimicrobial - impregnated catheters in preventing catheter - related infections during external ventricular drainage . compared with standard catheters , a significantly lower rate of csf infection was noticed for clindamycin / rifampin - impregnated catheters ( or 0.27 , 95% ci , 0.100.73 , p < 0.05 ) and for minocycline / rifampin - impregnated catheters ( or 0.11 , 95% ci , 0.060.21 , p < 0.05 ) . no statistical significance was found when standard catheters were compared with silver - impregnated catheters ( or 0.33 , 95% ci = 0.07 to 1.69 , p = 0.18 ) . in the meantime however several additional studies were published which assessed the efficacy of silver - impregnated catheters . winkler et al .   compared in their prospective randomized trial the rate of evd - related infections of 61 evd placements with either antibiotic - coated ( n = 32 ) or silver - bearing catheters ( n = 29 ) in 40 patients . regarding csf infection rate and dysfunction , no statistical significant differences between the two evd catheters bactiseal versus ventriguard were found . the rate of infections by catheter type was 7.6% ( 11/145 ) and 13.8% ( 4/29 ) for two different types of noncoated polyurethane catheters . silver - impregnated polyurethane catheters became infected in 6.1% ( 14 out of 228 ) . there was a significant difference in infection risk between the two study arms : 21.4% ( 30/140 ) for plain catheters versus 12.3% ( 17/138 ) for silver catheters ( p = 0.04 ) . in contrast to these studies , however , we could show a trend towards a higher infection rate in patients with a silver - coated evd catheter when compared to patients with nonimpregnated catheters ( 9% versus 2.3% ; p = 0.08 ) . selection bias can be excluded as the catheters were not available in our institution at the same time . because of the retrospective nature of the present study , various limitations must be mentioned . furthermore our findings might be limited due to the number of patients with evd - related infection which was smaller than infected and the small number of patients who were accommodated in single - bed rooms . many studies have been conducted to identify risk factors of evd - related infections . however , none of these risk factors could be confirmed in our cohort of patients . furthermore we could not show any difference in infection rates between patients who were placed in single- or multibed rooms , respectively .