***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 
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    ***EXAMPLES*** 
    Input: Objectives : To evaluate the effect of hormonal contraception including combined oral contraceptives ( COCs ) , and the injectable progestins depo-medroxyprogesterone acetate ( DMPA ) and norethisterone enanthate ( Net-En ) on the  risk of HIV acquisition among women in South Africa . Design / methods : We analyzed data from 5567 women aged 16–49 years participating in the Carraguard Phase 3 Efficacy Trial . Participants were interviewed about contraceptive use and sexual behaviors and underwent pelvic examinations and HIV testing quarterly . We used marginal structural Cox regression models to estimate the effect of hormonal contraception exposure on HIV acquisition risk among women overall and among young women ( 16–24 years ) in particular . Results : Two hundred and seventy participants became HIV-infected ( 3.7 per 100 woman-years ) ; HIV incidence was 2.8 , 4.6 , 3.5 and 3.4 per 100 woman-years in the COC , DMPA , Net-En and nonhormonal contraceptive groups , respectively ( P = 0.09 ) . The adjusted hazard ratios ( AHRs ) were 0.84 [ 95 % confidence interval ( CI ) 0.51–1.39 ] , 1.28 ( 95 % CI 0.92–1.78 ) and 0.92 ( 95 % CI 0.64–1.32 ) among COC , DMPA and Net-En users , respectively , compared with the nonhormonal group controlling for covariates . Age modified the effect of hormonal contraception on HIV acquisition risk ; among young women , the AHRs were 1.02 ( 95 % CI 0.46–2.28 ) for COCs , 1.68 ( 95 % CI 0.96–2.94 ) for DMPA and 1.36 ( 95 % CI0.78–2.35 ) for Net-En users . Conclusions : In this study conducted among South African women , hormonal contraception did not significantly increase the risk of HIV acquisition . However , the effect estimate does not rule out a moderate increase in HIV risk associated with DMPA use found in some other recent studies With two million new HIV infections annually , ongoing investigations of risk factors for HIV acquisition is critical to guide ongoing HIV prevention efforts . We conducted a prospect i ve cohort  analysis of HIV uninfected female sex workers enrolled at an HIV prevention clinic in Nairobi ( n = 1640 ) . In the initially HIV uninfected cohort ( 70 % ) , we observed 34 HIV infections during 1514 person-years of follow-up , i.e. an annual incidence of 2.2 % ( 95 % CI 1.6–3.1 % ) . In multivariable Cox Proportional Hazard analysis , HIV acquisition was associated with a shorter baseline duration of sex work ( aHR 0.76 , 95 % CI 0.63–0.91 ) , minimum charge/sex act ( aHR 2.74 , 0.82–9.15 , for low vs. intermediate ; aHR 5.70 , 1.96–16.59 , for high vs. intermediate ) , N. gonorrhoeae infection ( aAHR 5.89 , 95 % CI 2.03–17.08 ) , sex with casual clients during menses ( aHR 6.19 , 95 % CI 2.58–14.84 ) , Depo Provera use ( aHR 5.12 , 95 % CI 1.98–13.22 ) , and estimated number of annual unprotected regular partner contacts ( aHR 1.004 , 95 % CI 1.001–1.006 ) . Risk profiling based on baseline predictors suggested that substantial heterogeneity in HIV risk is evident , even within a key population . These data highlight several risk factors for HIV acquisition that could help to re-focus HIV prevention messages BACKGROUND Hormonal contraceptives are used widely but their effects on HIV-1 risk are unclear . We aim ed to assess the association between hormonal contraceptive use and risk of HIV-1 acquisition  by women and HIV-1 transmission from HIV-1-infected women to their male partners . METHODS In this prospect i ve study , we followed up 3790 heterosexual HIV-1-serodiscordant couples participating in two longitudinal studies of HIV-1 incidence in seven African countries . Among  injectable and oral hormonal contraceptive users and non-users , we compared rates of HIV-1 acquisition by women and HIV-1 transmission from women to men . The primary outcome measure was HIV-1 seroconversion . We used Cox proportional hazards regression and marginal structural modelling to assess the effect of contraceptive use on HIV-1 risk . FINDINGS Among 1314 couples in which the HIV-1-seronegative partner was female ( median follow-up 18·0 [ IQR 12·6 - 24·2 ] months ) , rates of HIV-1 acquisition were 6·61 per 100 person-years in women who used hormonal contraception and 3·78 per 100 person-years in those who did not ( adjusted hazard ratio 1·98 , 95 % CI 1·06 - 3·68 , p=0·03 ) . Among 2476 couples in which the HIV-1-seronegative partner was male ( median follow-up 18·7 [ IQR 12·8 - 24·2 ] months ) , rates of HIV-1 transmission from women to men were 2·61 per 100 person-years in couples in which women used hormonal contraception and 1·51 per 100 person-years in couples in which women did not use hormonal contraception ( adjusted hazard ratio 1·97 , 95 % CI 1·12 - 3·45 , p=0·02 ) . Marginal structural model analyses generated much the same results to the Cox proportional hazards regression . INTERPRETATION Women should be counselled about potentially increased risk of HIV-1 acquisition and transmission  with hormonal contraception , especially injectable methods , and about the importance of dual protection with condoms to decrease HIV-1 risk  . Non-hormonal or low-dose hormonal contraceptive methods should be considered for women with or at-risk for HIV-1 . FUNDING US National Institutes of Health and the Bill & Melinda Gates Foundation Vaginal Gel Versus HIV HIV prevention technologies for women are urgently needed , especially in sub-Saharan Africa where young women bear the greatest burden of the HIV epidemic . Abdool Karim et al. ( p. 1168 ; published online 19 July ) present the results of the CAPRISA 004 r and omized control trial . The nearly 3-year-long trial , conducted in urban and rural South African women , tested the efficacy of a vaginal gel containing the antiretroviral drug tenofovir in preventing HIV infection . The dosing strategy required application of the gel both before and after coitus , and with this regime HIV infection was reduced by approximately 39 % overall , by 54 % in women with high adherence to the protocol , and with no increase in overall adverse event rates . Tenofovir in a vaginal gel formulation shows significant protection against HIV infection in a r and omized control trial . The Centre for the AIDS Program of Research in South Africa ( CAPRISA ) 004 trial assessed the effectiveness and safety of a 1 % vaginal gel formulation of tenofovir , a nucleotide reverse transcriptase inhibitor , for the prevention of HIV acquisition in women . A double-blind , r and omized controlled trial was conducted comparing  tenofovir gel ( n = 445 women ) with  placebo gel ( n = 444 women ) in sexually active , HIV-uninfected 18- to 40-year-old women in urban and rural KwaZulu-Natal , South Africa .  HIV serostatus , safety , sexual behavior , and gel and condom use were assessed at monthly follow-up visits for 30 months . HIV incidence in the tenofovir gel arm was 5.6 per 100 women-years ( person time of study observation ) ( 38 out of 680.6 women-years ) compared with 9.1 per 100 women-years ( 60 out of 660.7 women-years ) in the placebo gel arm ( incidence rate ratio = 0.61 ; P = 0.017 ) . In high adherers ( gel adherence > 80 % ) , HIV incidence was 54 % lower ( P = 0.025 ) in the tenofovir gel arm . In intermediate adherers ( gel adherence 50 to 80 % ) and low adherers ( gel adherence < 50 % ) , the HIV incidence reduction was 38 and 28 % , respectively . Tenofovir gel  reduced HIV acquisition by an estimated 39 % overall , and by 54 % in women with high gel adherence . No increase in the overall adverse event rates was observed . There were no changes in viral load and no tenofovir resistance in HIV seroconverters . Tenofovir gel could potentially fill an important HIV prevention gap , especially for women unable to successfully negotiate mutual monogamy or condom use BACKGROUND Preexposure prophylaxis with antiretroviral drugs has been effective in the prevention of  human immunodeficiency virus ( HIV ) infection  in some trials but not in others . METHODS In this r and omized , double-blind , placebo-controlled trial , we assigned 2120 HIV-negative women in Kenya , South Africa , and Tanzania to receive either a combination of tenofovir disoproxil fumarate and emtricitabine ( TDF-FTC ) or placebo once daily . The primary objective was to assess the effectiveness of TDF-FTC  in preventing HIV acquisition and to evaluate safety . RESULTS HIV infections occurred in 33 women in the TDF-FTC group ( incidence rate , 4.7 per 100 person-years ) and in 35 in the placebo group ( incidence rate , 5.0 per 100 person-years ) , for an estimated hazard ratio in the TDF-FTC group of 0.94 ( 95 % confidence interval , 0.59 to 1.52 ; P=0.81 ) . The proportions of women with nausea , vomiting , or elevated alanine aminotransferase levels were significantly higher in the TDF-FTC group ( P=0.04 , P<0.001 , and P=0.03 , respectively ) . Rates of drug discontinuation because of hepatic or renal abnormalities were higher in the TDF-FTC group ( 4.7 % ) than in the placebo group ( 3.0 % , P=0.051 ) . Less than 40 % of the HIV-uninfected women in the TDF-FTC group had evidence of recent pill use at visits that were matched to the HIV-infection window for women with seroconversion . The study was stopped early , on April 18 , 2011 , because of lack of efficacy . CONCLUSIONS Prophylaxis with TDF-FTC did not significantly reduce the rate of HIV infection and was associated with increased rates of side effects , as compared with placebo . Despite substantial counseling efforts , drug adherence appeared to be low . ( Supported by the U.S. Agency for International Development and others ; FEM-PrEP Clinical Trials.gov number , NCT00625404 . ) The use of hormonal contraception has been associated with an increased risk of HIV-1  in some studies but not in others . We analysed data from a 10-year prospect i ve cohort study of female sex workers in Mombasa , Kenya . In multivariate analysis , women using the injectable contraceptive depot medroxyprogesterone acetate and women using oral contraceptive pills were at increased risk of HIV-1 acquisition compared with women using no contraceptive method Objective : To evaluate the effect of oral and injectable hormonal contraception on the  risk of HIV acquisition among women in South Africa and Zimbabwe . Design : Secondary data analysis of 4913 sexually active women aged 18–49 years followed for up to 24 months in the Methods for Improving Reproductive Health in Africa ( MIRA ) phase III effectiveness trial of the diaphragm and lubricant gel  for HIV prevention . Methods : Participants were interviewed quarterly about contraception and sexual behavior and were tested for pregnancy , HIV , and other sexually transmitted infections . We used a Cox proportional hazards marginal structural model , weighted by the inverse probability of hormonal contraception use , to compare the risk of HIV acquisition among nonpregnant women reporting use of combined oral contraceptive pills ( COC ) , progestin-only pills ( POP ) , and /or injectable hormonal contraception to women not using these methods . Results : During the study , 283 participants seroconverted . Use of oral contraceptives ( POP or COC ) was not associated with HIV risk [ adjusted hazard ratio ( HRa ) = 0.86 , 95 % confidence interval ( CI ) 0.32 , 1.78 ] . Injectable hormonal contraception was associated with a small nonsignificant risk of HIV infection ( HRa = 1.34 , 95 % CI 0.75 , 2.37 ) . The effect of injectable horm 
    Output:
    
The preponderance of data for oral contraceptive pills , injectable norethisterone enanthate , and levonorgestrel implants do not suggest an association with HIV acquisition , though data for implants are limited .
Although confounding in these observational data can not be excluded , new information increases concerns about  DMPA and HIV acquisition risk in women .