human
***task***
the task is to summarize an input biomedical literature in six sentences

***input***
the input is a biomedical literature

***output***
the output is the summary of an input biomedical literature in six sentences

***documentation***

***examples***

input: anemia has been shown to be the most frequent hematological abnormality in hiv - infected patients globally . even among those initiating antiretroviral therapy ( art ) , anemia has been demonstrated to be a strong risk factor for disease progression and subsequent death independent of cd4 count and viral load . in a large european cohort study , the presence of severe anemia at art initiation was associated with a 13-fold increased risk of death . in sub - saharan africa , which has the largest burden of hiv in the world , anemia is common as patients are more likely to be malnourished , have advanced immunosuppression , and have higher rates of comorbidities ( especially tuberculosis and malaria ) than those in high - income countries . despite the public health importance of anemia , prospective data from sub - saharan africa on its impact are limited . recent reports suggest that hemoglobin levels improve with art ; however , few studies have documented the evolution of hemoglobin levels among patients on art in resource - limited settings , and whether the effects on hemoglobin levels vary by art regimen . given the number of patients on art in this region , understanding the role of anemia in hiv treatment is critical to developing strategies to improve survival and reduce morbidity on art . the major cause of anemia is impaired erythropoiesis resulting from the release of inflammatory cytokines and decreased production of hematopoietic growth factors , coupled with malabsorption and impaired recycling of iron . additionally , there are multiple other causes of anemia , which include nutritional deficiencies ( iron , cobalamine , or folate deficiency ) , malignant bone marrow infiltration , bone marrow infection , and hemolysis . among patients initiating antiretroviral therapy , the use of zidovudine containingregimens has been associated with the incidence of anemia , and bone marrow toxicity has been postulated . amongst patients in an urban hiv clinic in uganda , these findings suggested that baseline severe anemia should not be used as a criterion for avoiding the use of zidovudine in patients initiating art in resource - limited settings . in this prospective cohort study conducted in johannesburg , south africa , we set out to determine the prevalence , incidence , and predictors of anemia among patients initiating first line art . we also sought to explore whether the degree of immunosuppression at art initiation or the initiating art regimen ( zidovudine versus other ) impacted the magnitude of hemoglobin increase while on treatment . the themba lethu clinic is one of the largest hiv care and treatment clinics in south africa with over 22,000 patients initiated onto art since 2004 . we included art nave , nonpregnant hiv - infected patients 18 years of age , initiated on standard first - line art at themba lethu from april 2004 to august 2009 with documented hemoglobin measurements . at themba lethu , art is provided according to the south african department of health guidelines . all patients are scheduled to have a full blood count at art initiation , four months after initiation , and then every six months thereafter . the laboratory data are captured onto a longitudinal patient management electronic record . with the full blood count measurements , whilst clinicians read the results , only hemoglobin valuesif initiated onto a zidovudine ( azt ) containing regimen , a full blood count is done at initiation , monthly for the first three months on treatment , and then every six months thereafter . only patients with a contraindication to stavudine ( d4 t ) at art initiation would be given azt in place of d4 t ( i.e. , pregnant women or patients receiving tuberculosis treatment ) . during the study period from april 2004 to august 2009 , the 2004 south africa national department of health hiv treatment guidelines were in force . for all patients , person - time accrued from art initiation until the date of the begining of ( 1 ) incident anemia ; ( 2 ) last clinic visit ; ( 3 ) loss to follow - up ; ( 4 ) death ; ( 5 ) transfer ; or ( 6 ) completion of 24 months of follow - up . loss to follow - up was defined as 4 months since last clinic visit . at themba lethu , mortality is ascertained via family or hospital report , active tracing , and linkage with the south african national vital registration infrastructure initiative . we used the national institutes of health division of aids definitions for grading the severity of adult and paediatric adverse events to define anemia . incident anemia was defined as new - onset anemia during the 24 month follow - up period among patients who were not anemic at initiation of art . we calculated the prevalence and incidence of anemia at art initiation and during follow - up , respectively . prevalence ratios ( pr ) and 95 % confidence intervals ( 95 % ci ) for the association of baseline characteristics with prevalent anemia were estimated using modified poisson regression . cox proportional hazards models were used to evaluate the association between incident anemia and baseline ( defined as 90 days before to 7 days after art initiation ) characteristics such as hemoglobin , cd4 count , body mass index ( bmi ) , and who stage . we further examined overall changes in hemoglobin levels on treatment by stratifying results by cd4 count and art regimen ( azt versus non - azt containing regimen ) at treatment initiation . use of themba lethu clinic data was approved by the human research ethics committee ( medical ) of the university of witwatersrand , and approval for analysis of anonymized data was approved by the boston university institutional review board . between april 2004 and august 2009 , 10,369 patients fulfilled the inclusion criteria . among these ,102 ( 1 % ) did not have hemoglobin measurements , and 8 patients had abnormally high hemoglobin levels ( 30 g / dl ) at art initiation leaving 10,259 patients for analysis . excluded patients were largely similar in demographic and clinical characteristics from those who were included in analyses . the majority of patients were females ( 68 % ) , with a median age of 36 years ( iqr 3143 ) and initiated on stavudine - lamivudine - efavirenz ( 89.4 % ) ( table 1 ) . the cohort was immunosuppressed at art initiation , with a median cd4 count of 82 cells / ml ( iqr 30151 ) , 45.7 % with whostage iii / iv , and 19.9 % with a tuberculosis diagnosis . overall prevalence of anemia at art initiation was 25.8 % ( 95 % ci : 25.0 % 26.7 % ) . in multivariable analysis , females ( pr : 1.77 ; 95 % ci : 1.641.90 ) and younger patients ( 1835 versus 55 ; pr : 1.59 ; 95 % ci : 1.192.11 ) were more likely to be anemic at art initiation ( table 2 ) , while patients initiated onto azt - based regimens ( versus d4t - based ) were less likely to be anaemic ( pr : 0.56 ; 95 % ci : 0.420.75 ) at the start of treatment . only 3.1 % ( n = 322 ) of the patients were initiated on to azt - based regimens . of note , among these 322 patients initiated onto azt - based regimens , 47 patients corresponding to 14.6 % already had hemoglobin levels of less than 10 g / dl at baseline . additionally , we found that those with a who iii / iv versus i / ii ( pr : 1.96 ; 95 % ci : 1.812.12 ) , patients with a low cd4 count ( 50 versus 200 cells / ml ; pr : 1.48 , 95 % ci : 1.281.73 ) , and those with tuberculosis at initiation ( pr : 1.14 , 95 % ci 1.061.22 ) were more likely to have anemia at art initiation . the incidence rate for anemia among these patients was 3.1 / 1000 person - years ( py ) . incidence of anemia was the highest in the first 3 months after art initiation at a rate of 34.7 / 1000 py and decreased to 16.7 / 1000 py between 3 and 6 months on treatment . this incidence was then fairly stable over the remaining 18 months of follow - up , between 7.7 and 8.4 / 1000 py . in adjusted analyses ( table 1 ) female gender ( adjusted hazards ratio ( ahr ) : 1.78 ; 95 % ci : 1.452.19 ) , lower bmi ( ahr : 1.70 ; 95 % ci : 1.352.14 ) , who iii / iv ( ahr : 1.24 ; 95 % ci : 1.021.51 ) , and lower cd4 count ( 50 versus 200 cells / ml , ahr : 1.72 ; 95 % ci : 1.182.52 ) were associated with increased incident anemia over the follow - up period . we found that azt use was associated with over twice the rate of developing anemia during follow - up ( ahr : 2.19 ; 95 % ci : 1.503.20 ) . in a sensitivity analysis to decrease measurement errorour hazard ratios were similar though the association between azt and incident anemia was slightly attenuated , from 2.19 to 1.88 ( 95 % ci : 1.173.03 ) . among the 10,259 patients initiating art , hemoglobin increased over 24 months on art ( figure 1 ) . between 0 and 3 months on art , mean hemoglobin was 11.2 g / dl but increased to 13.6 g / dl between 21 and 24 months . regardless of cd4 at art initiation , hemoglobin levels increased over time . between 06 months on art , the magnitude of hemoglobin increase was linearly related to cd4 count . however , between 6 and 24 months on art , hemoglobin levels showed a sustained overall increase , the magnitude of which was similar regardless of baseline cd4 count . at art initiation , patients on azt containing regimens had higher mean hemoglobin ( mean 12.0 g / dl , sd 2.0 ) compared to those initiated onto regimens without azt ( mean 11.4 g / dl , sd 2.2 ) . from 6 and 24 months on art , mean hemoglobin increased for both regimen categories . for patients on azt containing regimens , mean hemoglobin increased from 12.3 g / dl to 13.3 g / dl , and for patients on regimens without azt , mean hemoglobin increased from 12.6 g / dl at initiation to 13.4 g / dl by 24 months . this is a study of patients under routine public - sector hiv care in johannesburg , south africa , over a quarter of patients presented at treatment initiation with anemia ( hb 10 g / dl ) . this is slightly higher than previous estimate of 18 % of prevalence of anemia among hiv - infected patients in southern africa but in line with estimates for other regions of africa ( between 24 % and 37 % ) . we estimate the incidence of anemia at 3.1 / 1000 person - years and found it to be the highest in the first 6 months after art initiation . since hemoglobin measurements are simple and inexpensive , monitoring hemoglobin levels over the first 6 months on art among patients at high risk may allow for improved detection of hiv - related anemia . it may also lead to detection of related underlying comorbid illnesses manifesting as anemia associated with poor treatment outcomes . beyond 6 months , our data shows a lower incidence of anemia in support of current recommendations to measure hemoglobin levels every 6 months and if clinically indicated during this time . in our data , incident anemia was associated with female gender , lower bmi , advanced who stage , and lower cd4 count . the association of anemia with lower bmi is likely to reflect malnutrition , as a number of nutritional deficiencies contribute to anemia . the increased risk in anemia among patients with immunosuppression is in agreement with previous published reports . studies have shown that azt can inhibit bone marrow activity , resulting in decreased production of blood cells and platelets ; previous research has demonstrated its association with incident anemia . the present study also showed that over 24 months of follow - up , hemoglobin increased for patients initiating art , similar to findings from resource - rich environments . this increase in hemoglobin was seen regardless of art regimen ( both azt - and d4t - based regimens ) . this observation is in contrast to a meta - analysis of six clinical trials conducted in high - income settings that reported decreases in hemoglobin levels during 48 weeks of follow - up among patients initiating azt containing regimens . however , in a cohort of hiv - infected patients accessing art from a rural hospital in tanzania , the majority of patients who were anemic at the time of art initiation had significant hemoglobin increase over the initial 12 months of art , and in this study , zidovudine - containing initial regimen was an independent predictor of persistent anemia . this pattern of improving hemoglobin level despite initiating an azt - containing regimen is also similar to observations in some south african and ugandan cohorts . our study has several strengths including large number of clinical events owing to the relatively large sample size . we did not collect comprehensive information of clinical conditions that may be possible underlying causes of anemia , resulting in unmeasured confounding of the risk factors for prevalent and incident anemia . additionally , loss to follow - up may have led to selection bias , as outcome can not be determined in patients lost or those who have died . in conclusion , we observed a high prevalence of anemia among hiv - infected patients initiating first - line art in johannesburg , south africa . over 24 months of follow - up , incidence of anemia was the highest in the first 6 months after art initiation , but , overall , during follow - up , this remained low . our results further support findings that art improves hemoglobin and this is seen regardless of regimen type ( azt containing versus non - azt containing ) and the degree of immunosuppression . hemoglobin measurement is an inexpensive marker for hiv disease progression and should be measured more frequently in patients at risk for anemia in the first 6 months after initiation of art . our study suggests that art improves hemoglobin levels regardless of magnitude of immunosuppression and art initiating regimen .
output:

agent
among those with hiv , anemia is a strong risk factor for disease progression and death independent of cd4 count and viral load . understanding the role of anemia in hiv treatment is critical to developing strategies to reduce morbidity and mortality . we conducted a prospective analysis among 10,259 hiv - infected adults initiating first - line art between april 2004 and august 2009 in johannesburg , south africa . the prevalence of anemia at art initiation was 25.8 % . mean hemoglobin increased independent of baseline cd4 . females , lower bmi , who stage iii / iv , lower cd4 count , and zidovudine use were associated with increased risk of developing anemia during follow - up . after initiation of art , hemoglobin improved , regardless of regimen type and the degree of immunosuppression . between 0 and 6 months on art , the magnitude of hemoglobin increase was linearly related to cd4 count . however , between 6 and 24 months on art , hemoglobin levels showed a sustained overall increase , the magnitude of which was similar regardless of baseline cd4 level . this increase in hemoglobin was seen even among patients on zidovudine containing regimens . since low hemoglobin is an established adverse prognostic marker , prompt identification of anemia may result in improved morbidity and mortality of patients initiating art .
***task***
the task is to summarize an input biomedical literature in six sentences

***input***
the input is a biomedical literature

***output***
the output is the summary of an input biomedical literature in six sentences

***documentation***

***examples***

input: anemia has been shown to be the most frequent hematological abnormality in hiv - infected patients globally . even among those initiating antiretroviral therapy ( art ) , anemia has been demonstrated to be a strong risk factor for disease progression and subsequent death independent of cd4 count and viral load . in a large european cohort study , the presence of severe anemia at art initiation was associated with a 13-fold increased risk of death . in sub - saharan africa , which has the largest burden of hiv in the world , anemia is common as patients are more likely to be malnourished , have advanced immunosuppression , and have higher rates of comorbidities ( especially tuberculosis and malaria ) than those in high - income countries . despite the public health importance of anemia , prospective data from sub - saharan africa on its impact are limited . recent reports suggest that hemoglobin levels improve with art ; however , few studies have documented the evolution of hemoglobin levels among patients on art in resource - limited settings , and whether the effects on hemoglobin levels vary by art regimen . given the number of patients on art in this region , understanding the role of anemia in hiv treatment is critical to developing strategies to improve survival and reduce morbidity on art . the major cause of anemia is impaired erythropoiesis resulting from the release of inflammatory cytokines and decreased production of hematopoietic growth factors , coupled with malabsorption and impaired recycling of iron . additionally , there are multiple other causes of anemia , which include nutritional deficiencies ( iron , cobalamine , or folate deficiency ) , malignant bone marrow infiltration , bone marrow infection , and hemolysis . among patients initiating antiretroviral therapy , the use of zidovudine containingregimens has been associated with the incidence of anemia , and bone marrow toxicity has been postulated . amongst patients in an urban hiv clinic in uganda , these findings suggested that baseline severe anemia should not be used as a criterion for avoiding the use of zidovudine in patients initiating art in resource - limited settings . in this prospective cohort study conducted in johannesburg , south africa , we set out to determine the prevalence , incidence , and predictors of anemia among patients initiating first line art . we also sought to explore whether the degree of immunosuppression at art initiation or the initiating art regimen ( zidovudine versus other ) impacted the magnitude of hemoglobin increase while on treatment . the themba lethu clinic is one of the largest hiv care and treatment clinics in south africa with over 22,000 patients initiated onto art since 2004 . we included art nave , nonpregnant hiv - infected patients 18 years of age , initiated on standard first - line art at themba lethu from april 2004 to august 2009 with documented hemoglobin measurements . at themba lethu , art is provided according to the south african department of health guidelines . all patients are scheduled to have a full blood count at art initiation , four months after initiation , and then every six months thereafter . the laboratory data are captured onto a longitudinal patient management electronic record . with the full blood count measurements , whilst clinicians read the results , only hemoglobin valuesif initiated onto a zidovudine ( azt ) containing regimen , a full blood count is done at initiation , monthly for the first three months on treatment , and then every six months thereafter . only patients with a contraindication to stavudine ( d4 t ) at art initiation would be given azt in place of d4 t ( i.e. , pregnant women or patients receiving tuberculosis treatment ) . during the study period from april 2004 to august 2009 , the 2004 south africa national department of health hiv treatment guidelines were in force . for all patients , person - time accrued from art initiation until the date of the begining of ( 1 ) incident anemia ; ( 2 ) last clinic visit ; ( 3 ) loss to follow - up ; ( 4 ) death ; ( 5 ) transfer ; or ( 6 ) completion of 24 months of follow - up . loss to follow - up was defined as 4 months since last clinic visit . at themba lethu , mortality is ascertained via family or hospital report , active tracing , and linkage with the south african national vital registration infrastructure initiative . we used the national institutes of health division of aids definitions for grading the severity of adult and paediatric adverse events to define anemia . incident anemia was defined as new - onset anemia during the 24 month follow - up period among patients who were not anemic at initiation of art . we calculated the prevalence and incidence of anemia at art initiation and during follow - up , respectively . prevalence ratios ( pr ) and 95 % confidence intervals ( 95 % ci ) for the association of baseline characteristics with prevalent anemia were estimated using modified poisson regression . cox proportional hazards models were used to evaluate the association between incident anemia and baseline ( defined as 90 days before to 7 days after art initiation ) characteristics such as hemoglobin , cd4 count , body mass index ( bmi ) , and who stage . we further examined overall changes in hemoglobin levels on treatment by stratifying results by cd4 count and art regimen ( azt versus non - azt containing regimen ) at treatment initiation . use of themba lethu clinic data was approved by the human research ethics committee ( medical ) of the university of witwatersrand , and approval for analysis of anonymized data was approved by the boston university institutional review board . between april 2004 and august 2009 , 10,369 patients fulfilled the inclusion criteria . among these ,102 ( 1 % ) did not have hemoglobin measurements , and 8 patients had abnormally high hemoglobin levels ( 30 g / dl ) at art initiation leaving 10,259 patients for analysis . excluded patients were largely similar in demographic and clinical characteristics from those who were included in analyses . the majority of patients were females ( 68 % ) , with a median age of 36 years ( iqr 3143 ) and initiated on stavudine - lamivudine - efavirenz ( 89.4 % ) ( table 1 ) . the cohort was immunosuppressed at art initiation , with a median cd4 count of 82 cells / ml ( iqr 30151 ) , 45.7 % with whostage iii / iv , and 19.9 % with a tuberculosis diagnosis . overall prevalence of anemia at art initiation was 25.8 % ( 95 % ci : 25.0 % 26.7 % ) . in multivariable analysis , females ( pr : 1.77 ; 95 % ci : 1.641.90 ) and younger patients ( 1835 versus 55 ; pr : 1.59 ; 95 % ci : 1.192.11 ) were more likely to be anemic at art initiation ( table 2 ) , while patients initiated onto azt - based regimens ( versus d4t - based ) were less likely to be anaemic ( pr : 0.56 ; 95 % ci : 0.420.75 ) at the start of treatment . only 3.1 % ( n = 322 ) of the patients were initiated on to azt - based regimens . of note , among these 322 patients initiated onto azt - based regimens , 47 patients corresponding to 14.6 % already had hemoglobin levels of less than 10 g / dl at baseline . additionally , we found that those with a who iii / iv versus i / ii ( pr : 1.96 ; 95 % ci : 1.812.12 ) , patients with a low cd4 count ( 50 versus 200 cells / ml ; pr : 1.48 , 95 % ci : 1.281.73 ) , and those with tuberculosis at initiation ( pr : 1.14 , 95 % ci 1.061.22 ) were more likely to have anemia at art initiation . the incidence rate for anemia among these patients was 3.1 / 1000 person - years ( py ) . incidence of anemia was the highest in the first 3 months after art initiation at a rate of 34.7 / 1000 py and decreased to 16.7 / 1000 py between 3 and 6 months on treatment . this incidence was then fairly stable over the remaining 18 months of follow - up , between 7.7 and 8.4 / 1000 py . in adjusted analyses ( table 1 ) female gender ( adjusted hazards ratio ( ahr ) : 1.78 ; 95 % ci : 1.452.19 ) , lower bmi ( ahr : 1.70 ; 95 % ci : 1.352.14 ) , who iii / iv ( ahr : 1.24 ; 95 % ci : 1.021.51 ) , and lower cd4 count ( 50 versus 200 cells / ml , ahr : 1.72 ; 95 % ci : 1.182.52 ) were associated with increased incident anemia over the follow - up period . we found that azt use was associated with over twice the rate of developing anemia during follow - up ( ahr : 2.19 ; 95 % ci : 1.503.20 ) . in a sensitivity analysis to decrease measurement errorour hazard ratios were similar though the association between azt and incident anemia was slightly attenuated , from 2.19 to 1.88 ( 95 % ci : 1.173.03 ) . among the 10,259 patients initiating art , hemoglobin increased over 24 months on art ( figure 1 ) . between 0 and 3 months on art , mean hemoglobin was 11.2 g / dl but increased to 13.6 g / dl between 21 and 24 months . regardless of cd4 at art initiation , hemoglobin levels increased over time . between 06 months on art , the magnitude of hemoglobin increase was linearly related to cd4 count . however , between 6 and 24 months on art , hemoglobin levels showed a sustained overall increase , the magnitude of which was similar regardless of baseline cd4 count . at art initiation , patients on azt containing regimens had higher mean hemoglobin ( mean 12.0 g / dl , sd 2.0 ) compared to those initiated onto regimens without azt ( mean 11.4 g / dl , sd 2.2 ) . from 6 and 24 months on art , mean hemoglobin increased for both regimen categories . for patients on azt containing regimens , mean hemoglobin increased from 12.3 g / dl to 13.3 g / dl , and for patients on regimens without azt , mean hemoglobin increased from 12.6 g / dl at initiation to 13.4 g / dl by 24 months . this is a study of patients under routine public - sector hiv care in johannesburg , south africa , over a quarter of patients presented at treatment initiation with anemia ( hb 10 g / dl ) . this is slightly higher than previous estimate of 18 % of prevalence of anemia among hiv - infected patients in southern africa but in line with estimates for other regions of africa ( between 24 % and 37 % ) . we estimate the incidence of anemia at 3.1 / 1000 person - years and found it to be the highest in the first 6 months after art initiation . since hemoglobin measurements are simple and inexpensive , monitoring hemoglobin levels over the first 6 months on art among patients at high risk may allow for improved detection of hiv - related anemia . it may also lead to detection of related underlying comorbid illnesses manifesting as anemia associated with poor treatment outcomes . beyond 6 months , our data shows a lower incidence of anemia in support of current recommendations to measure hemoglobin levels every 6 months and if clinically indicated during this time . in our data , incident anemia was associated with female gender , lower bmi , advanced who stage , and lower cd4 count . the association of anemia with lower bmi is likely to reflect malnutrition , as a number of nutritional deficiencies contribute to anemia . the increased risk in anemia among patients with immunosuppression is in agreement with previous published reports . studies have shown that azt can inhibit bone marrow activity , resulting in decreased production of blood cells and platelets ; previous research has demonstrated its association with incident anemia . the present study also showed that over 24 months of follow - up , hemoglobin increased for patients initiating art , similar to findings from resource - rich environments . this increase in hemoglobin was seen regardless of art regimen ( both azt - and d4t - based regimens ) . this observation is in contrast to a meta - analysis of six clinical trials conducted in high - income settings that reported decreases in hemoglobin levels during 48 weeks of follow - up among patients initiating azt containing regimens . however , in a cohort of hiv - infected patients accessing art from a rural hospital in tanzania , the majority of patients who were anemic at the time of art initiation had significant hemoglobin increase over the initial 12 months of art , and in this study , zidovudine - containing initial regimen was an independent predictor of persistent anemia . this pattern of improving hemoglobin level despite initiating an azt - containing regimen is also similar to observations in some south african and ugandan cohorts . our study has several strengths including large number of clinical events owing to the relatively large sample size . we did not collect comprehensive information of clinical conditions that may be possible underlying causes of anemia , resulting in unmeasured confounding of the risk factors for prevalent and incident anemia . additionally , loss to follow - up may have led to selection bias , as outcome can not be determined in patients lost or those who have died . in conclusion , we observed a high prevalence of anemia among hiv - infected patients initiating first - line art in johannesburg , south africa . over 24 months of follow - up , incidence of anemia was the highest in the first 6 months after art initiation , but , overall , during follow - up , this remained low . our results further support findings that art improves hemoglobin and this is seen regardless of regimen type ( azt containing versus non - azt containing ) and the degree of immunosuppression . hemoglobin measurement is an inexpensive marker for hiv disease progression and should be measured more frequently in patients at risk for anemia in the first 6 months after initiation of art . our study suggests that art improves hemoglobin levels regardless of magnitude of immunosuppression and art initiating regimen .
output:
