***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: Background : In the And ean Region , HIV and sexually transmitted infections ( STI ) are most prevalent among men who have sex with men ( MSM ) , but incidence estimates and associated factors have never been prospect ively assessed . Methods : A cohort of 1056 high-risk HIV-negative MSM in Lima , Peru , were recruited during 1998 - 2000 ( the ALASKA Cohort ) , and a nested case-control analysis was conducted between seroconverters and nonseroconverters , matched 1:3 by age and duration of follow-up for comparison of risk behaviors , acute retroviral symptoms , circumcision , and STI . Results : During average follow-up of 335 days , 34 men seroconverted , providing a HIV incidence estimate of 3.5 per 100 person-years [ 95 % confidence interval ( CI ) : 2.3 to 4.7 ] . High syphilis ( 8.4 per 100 person-years , 95 % CI : 6.7 to 10.1 ) and herpes simplex virus type 2 ( HSV-2 ) infection ( 10.4 per 100 person-years , 95 % CI : 8.6 to 11.9 ) incidence estimates were obtained . HIV seroconverters were more likely than men who remained seronegative to report fever ≥3 days ( 46 % vs. 7 % ) , to seek medical care ( 62 % vs. 27 % ) , and to have ≥1 casual partner ( 86.2 % vs. 74.1 % ) since their last visit . HIV seroconverters also were more likely to have acquired syphilis or HSV-2 infection ( 31 % vs. 8 % among initially HSV-2-seronegative men ) although they were less likely to be circumcised ( 4.2 % vs. 20.6 % , a nonsignificant difference ) . In multivariate analysis , incident syphilis or HSV-2 infection ( odds ratio [ OR ] : 5.9 , 95 % CI : 1.5 to 22.7 ) and sex with any casual partner ( OR : 4.8 , 95 % CI : 0.9 to 26.2 ) were associated with HIV seroconversion . Conclusions : STI that may cause anogenital ulcers are important risk factors for HIV acquisition among high-risk MSM in Lima , a population with a very high HIV incidence estimate . Synergistic interventions focusing in preventing both HIV and HSV-2 , like male circumcision , are warranted to be assessed , especially in MSM population s with low levels of circumcision and high incidence estimates of ulcerative STI BACKGROUND Observational data and non-human primate challenge studies suggest that cell-mediated immune responses might provide control of HIV replication . The Step Study directly assessed the efficacy of a cell-mediated immunity vaccine to protect against  HIV-1 infection or change in early plasma HIV-1 levels . METHODS We undertook a double-blind , phase II , test-of-concept study at 34 sites in North America , the Caribbean , South America , and Australia . We r and omly assigned 3000 HIV-1-seronegative participants by computer-generated assignments to receive three injections of MRKAd5 HIV-1 gag/pol/nef vaccine  ( n=1494 ) or placebo  ( n=1506 ) . R and omisation was prestratified by sex , adenovirus type 5 ( Ad5 ) antibody titre at baseline , and study site . Primary objective was a reduction in HIV-1 acquisition rates ( tested every 6 months ) or a decrease in HIV-1 viral-load setpoint ( early plasma HIV-1 RNA measured 3 months after HIV-1 diagnosis ) . Analyses were per protocol and modified intention to treat . The study was stopped early because it unexpectedly met the prespecified futility boundaries at the first interim analysis . This study is registered with Clinical Trials.gov , number NCT00095576 . FINDINGS In a prespecified interim analysis in participants with baseline Ad5 antibody titre 200 or less , 24 ( 3 % ) of 741 vaccine recipients became HIV-1 infected versus 21 ( 3 % ) of 762 placebo recipients ( hazard ratio [ HR ] 1.2 [ 95 % CI 0.6 - 2.2 ] ) . All but one infection occurred in men . The corresponding geometric mean plasma HIV-1 RNA was comparable in infected male vaccine and placebo recipients ( 4.61 vs 4.41 log(10 ) copies per mL , one tailed p value for potential benefit 0.66 ) . The vaccine elicited interferon-gamma ELISPOT responses in 75 % ( 267 ) of the 25 % r and om sample of all vaccine recipients ( including both low and high Ad5 antibody titres ) on whose specimens this testing was done ( n=354 ) . In exploratory analyses of all study volunteers , irrespective of baseline Ad5 antibody titre , the HR of HIV-1 infection between vaccine and placebo recipients was higher in Ad5 seropositive men ( HR 2.3 [ 95 % CI 1.2 - 4.3 ] ) and uncircumcised men ( 3.8 [ 1.5 - 9.3 ] ) , but was not increased in Ad5 seronegative ( 1.0 [ 0.5 - 1.9 ] ) or circumcised ( 1.0 [ 0.6 - 1.7 ] ) men . INTERPRETATION This cell-mediated immunity vaccine did not prevent HIV-1 infection or reduce early viral level . Mechanisms for insufficient efficacy of the vaccine and the increased HIV-1 infection rates in subgroups of vaccine recipients are being explored BACKGROUND Male circumcision could provide substantial protection against acquisition of HIV-1 infection . Our aim was to determine whether male circumcision had a protective effect against HIV infection , and to assess safety and changes in sexual behaviour related to this intervention . METHODS We did a r and omised controlled trial of 2784 men aged 18 - 24 years in Kisumu , Kenya . Men were r and omly assigned to an intervention group ( circumcision ; n=1391 ) or a control group ( delayed circumcision , 1393 ) , and assessed by  HIV testing , medical examinations , and behavioural interviews during follow-ups at 1 , 3 , 6 , 12 , 18 , and 24 months . HIV seroincidence was estimated in an intention-to-treat analysis . This trial is registered with Clinical Trials.gov , with the number NCT00059371 . FINDINGS The trial was stopped early on December 12 , 2006 , after a third interim analysis review ed by the data and safety monitoring board . The median length of follow-up was 24 months . Follow-up for HIV status was incomplete for 240 ( 8.6 % ) participants . 22 men in the intervention group and 47 in the control group had tested positive for HIV when the study was stopped . The 2-year HIV incidence was 2.1 % ( 95 % CI 1.2 - 3.0 ) in the circumcision group and 4.2 % ( 3.0 - 5.4 ) in the control group ( p=0.0065 ) ; the relative risk of HIV infection in circumcised men was 0.47 ( 0.28 - 0.78 ) , which corresponds to a reduction in the risk of acquiring an HIV infection of 53 % ( 22 - 72 ) . Adjusting for non-adherence to treatment and excluding four men found to be seropositive at enrollment , the protective effect of circumcision was 60 % ( 32 - 77 ) . Adverse events related to the intervention ( 21 events in 1.5 % of those circumcised ) resolved quickly . No behavioural risk compensation after circumcision was observed . INTERPRETATION Male circumcision significantly reduces the risk of HIV acquisition in young men in Africa . Where appropriate , voluntary , safe , and affordable circumcision services should be integrated with other HIV preventive interventions and provided as expeditiously as possible Background Black men who have sex with men ( MSM ) in the United States ( US ) are affected by HIV at disproportionate rates compared to MSM of other race/ethnicities . Current HIV incidence estimates in this group are needed to appropriately target prevention efforts . Methods From July 2009 to October 2010 , Black MSM reporting unprotected anal intercourse with a man in the past six months were enrolled and followed for one year in six US cities for a feasibility study of a multi-component intervention to reduce HIV infection  . HIV incidence based on HIV seroconversion was calculated as number of events/100 person-years . Multivariate proportional hazards modeling with time-dependent covariates was used to identify correlates of HIV acquisition . Results Of 1,553 Black MSM enrolled , 1,164 were HIV-uninfected at baseline and included in follow-up . Overall annual HIV incidence was 3.0 % ( 95 % confidence interval ( CI ) : 2.0 , 4.4 % ) and 5.9 % among men ≤30 years old ( 95 % CI : 3.6 , 9.1 % ) . Men ≤30 years old reported significantly higher levels of sexual risk and were more likely to have a sexually transmitted infection diagnosed during follow-up . Younger men also were more likely to not have a usual place for health care , not have visited a health care provider recently , and to have unmet health care needs . In multivariate analysis , age ≤30 years ( hazard ratio ( HR ) : 3.4 ; 95 % CI : 1.4 , 8.3 ) and unprotected receptive anal intercourse with HIV-positive or unknown status partners ( HR : 4.1 ; 95 % CI : 1.9 , 9.1 ) were significantly associated with HIV acquisition . Conclusion In the largest cohort of prospect ively-followed Black MSM in the US  , HIV incidence was high , particularly among young men . Targeted , tailored and culturally appropriate HIV prevention strategies incorporating behavioral , social and biomedical based interventions are urgently needed to lower these rates Background Observational studies suggest that male circumcision may provide protection against HIV-1 infection .  A r and omized , controlled intervention trial was conducted in a general population of South Africa to test this hypothesis . Methods and Findings A total of 3,274 uncircumcised men , aged 18–24 y , were r and omized to a control or an intervention group with follow-up visits at months 3 , 12 , and 21 . Male circumcision was offered to the intervention group immediately after r and omization and to the control group at the end of the follow-up . The grouped censored data were analyzed in intention-to-treat , univariate and multivariate , analyses , using piecewise exponential , proportional hazards models . Rate ratios ( RR ) of HIV incidence were determined with 95 % CI . Protection against HIV infection was calculated as 1 − RR . The trial was stopped at the interim analysis , and the mean ( interquartile range ) follow-up was 18.1 mo ( 13.0–21.0 ) when the data were analyzed . There were 20 HIV infections ( incidence rate = 0.85 per 100 person-years ) in the intervention group and 49 ( 2.1 per 100 person-years ) in the control group , corresponding to an RR of 0.40 ( 95 % CI : 0.24%–0.68 % ; p < 0.001 ) . This RR corresponds to a protection of 60 % ( 95 % CI : 32%–76 % ) . When controlling for behavioural factors , including sexual behaviour that increased slightly in the intervention group , condom use , and health-seeking behaviour , the protection was of 61 % ( 95 % CI : 34%–77 % ) . Conclusion Male circumcision provides a degree of protection against acquiring HIV infection , equivalent to what a vaccine of high efficacy would have achieved . Male circumcision may provide an important way of reducing the spread of HIV infection in sub-Saharan Africa . ( Preliminary and partial results were presented at the International AIDS Society 2005 Conference , on 26 July 2005 , in Rio de Janeiro , Brazil . Background The Step Study found that men who had sex with men ( MSM ) who received an adenovirus type 5 ( Ad5 ) vector – based vaccine and were uncircumcised or had prior Ad5 immunity , had a higher HIV incidence than MSM who received placebo .  We investigated whether differences in HIV exposure , measured by reported sexual risk behaviors , may explain the increased risk . Methods Among 1764 MSM in the trial , 726 were uncircumcised , 994 had prior Ad5 immunity , and 563 were both uncircumcised and had prior Ad5 immunity . Analyses compared sexual risk behaviors and perceived treatment assignment among vaccine and placebo recipients , determined risk factors for HIV acquisition , and examined the role of insertive anal intercourse in HIV risk among uncircumcised men . Results Few sexual risk behaviors were significantly higher in vaccine versus placebo recipients at baseline or during follow-up . Among uncircumcised men , vaccine recipients at baseline were more likely to report unprotected insertive anal intercourse with HIV-negative partners ( 24.9 % vs. 18.1 % ; P = 0.03 ) . Among uncircumcised 
    Output:
    
Our meta-analyses may suggest a protective effect of voluntary medical male circumcision against HIV infection among men who have sex with men , especially in setting s like Asia/Africa