***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 Preexposure prophylaxis with antiretroviral agents has been shown to reduce the transmission of human immunodeficiency virus ( HIV ) among men who have sex with men ; however , the efficacy among heterosexuals is uncertain . METHODS We r and omly assigned HIV-seronegative men and women to receive either tenofovir disoproxil fumarate and emtricitabine ( TDF-FTC ) or matching placebo once daily . Monthly study visits were scheduled , and participants received a comprehensive package of prevention services , including HIV testing , counseling on adherence to medication , management of sexually transmitted infections , monitoring for adverse events , and individualized counseling on risk reduction ; bone mineral density testing was performed semiannually in a subgroup of participants . RESULTS A total of 1219 men and women underwent r and omization ( 45.7 % women ) and were followed for 1563 person-years ( median , 1.1 years ; maximum , 3.7 years ) . Because of low retention and logistic limitations , we concluded the study early and followed enrolled participants through an orderly study closure rather than exp and ing enrollment . The TDF-FTC group had higher rates of nausea ( 18.5 % vs. 7.1 % , P<0.001 ) , vomiting ( 11.3 % vs. 7.1 % , P=0.008 ) , and dizziness ( 15.1 % vs. 11.0 % , P=0.03 ) than the placebo group , but the rates of serious adverse events were similar ( P=0.90 ) . Participants who received TDF-FTC , as compared with those who received placebo , had a significant decline in bone mineral density . K65R , M184V , and A62V resistance mutations developed in 1 participant in the TDF-FTC group who had had an unrecognized acute HIV infection at enrollment . In a modified intention-to-treat analysis that included the 33 participants who became infected during the study ( 9 in the TDF-FTC group and 24 in the placebo group ; 1.2 and 3.1 infections per 100 person-years , respectively ) , the efficacy of TDF-FTC was 62.2 % ( 95 % confidence interval , 21.5 to 83.4 ; P=0.03 ) . CONCLUSIONS Daily TDF-FTC prophylaxis prevented HIV infection in sexually active heterosexual adults . The long-term safety of daily TDF-FTC prophylaxis , including the effect on bone mineral density , remains unknown . ( Funded by the Centers for Disease Control and Prevention and the National Institutes of Health ; TDF2 Clinical Trials.gov number , NCT00448669 . ) ABSTRACT Antiretroviral therapy ( ART ) has transformed HIV into a manageable illness . However , high levels of adherence must be maintained . Lack of access to basic re sources ( food , transportation , and housing ) has been consistently associated with suboptimal ART adherence . Moving beyond such direct effects , this study takes a hierarchical re sources approach in which the effects of access to basic re sources on ART adherence are mediated through interpersonal re sources ( social support and care services ) and personal re sources ( self-efficacy ) . Participants were 915 HIV-positive men and women living in Atlanta , GA , recruited from community centers and infectious disease clinics . Participants answered baseline question naires , and provided prospect i ve data on ART adherence . Across a series of nested models , a consistent pattern emerged whereby lack of access to basic re sources had indirect , negative effects on adherence , mediated through both lack of access to social support and services , and through lower treatment self-efficacy . There was also a significant direct effect of lack of access to transportation on adherence . Lack of access to basic re sources negatively impacts ART adherence . Effects for housing instability and food insecurity were fully mediated through social support , access to services , and self-efficacy , highlighting these as important targets for intervention . Targeting service supports could be especially beneficial due to the potential to both promote adherence and to link clients with other services to supplement food , housing , and transportation . Inability to access transportation had a direct negative effect on adherence , suggesting that free or reduced cost transportation could positively impact ART adherence among disadvantaged population BACKGROUND Antiretroviral pre-exposure prophylaxis reduces sexual transmission of HIV . We assessed whether daily oral use of tenofovir disoproxil fumarate ( tenofovir ) , an antiretroviral , can reduce HIV transmission in injecting drug users . METHODS In this r and omised , double-blind , placebo-controlled trial , we enrolled volunteers from 17 drug-treatment clinics in Bangkok , Thail and . Participants were eligible if they were aged 20 - 60 years , were HIV-negative , and reported injecting drugs during the previous year . We r and omly assigned participants ( 1:1 ; blocks of four ) to either tenofovir or placebo using a computer-generated r and omisation sequence . Participants chose either daily directly observed treatment or monthly visits and could switch at monthly visits . Participants received monthly HIV testing and individualised risk-reduction and adherence counselling , blood safety assessment s every 3 months , and were offered condoms and methadone treatment . The primary efficacy endpoint was HIV infection , analysed by modified intention-to-treat analysis . This trial is registered with Clinical Trials.gov , number NCT00119106 . FINDINGS Between June 9 , 2005 , and July 22 , 2010 , we enrolled 2413 participants , assigning 1204 to tenofovir and 1209 to placebo .  Two participants had HIV at enrolment and 50 became infected during follow-up : 17 in the tenofovir group ( an incidence of 0·35 per 100 person-years ) and 33 in the placebo group ( 0·68 per 100 person-years ) , indicating a 48·9 % reduction in HIV incidence ( 95 % CI 9·6 - 72·2 ; p=0·01 ) . The occurrence of serious adverse events was much the same between the two groups ( p=0·35 ) . Nausea was more common in participants in the tenofovir group than in the placebo group ( p=0·002 ) . INTERPRETATION In this study , daily oral tenofovir reduced the risk of HIV infection in people who inject drugs . Pre-exposure prophylaxis with tenofovir can now be considered for use as part of an HIV prevention package for people who inject drugs . FUNDING US Centers for Disease Control and Prevention and the Bangkok Metropolitan Administration Objective : To describe participant adherence to daily oral tenofovir in an HIV preexposure prophylaxis ( PrEP ) trial , examine factors associated with adherence , and assess the impact of adherence on the risk of HIV infection . Design : The Bangkok Tenofovir Study was a r and omized , double-blind ,  placebo-controlled trial conducted among people who inject drugs , 2005–2012 . Methods : Participants chose daily visits or monthly visits . Study nurses observed participants swallow study drug and both initialed a diary . We assessed adherence using the diary . We examined adherence by age group and sex and used logistic regression to evaluate demographics and risk behaviors as predictors of adherence and Cox regression to assess the impact of adherence on the risk of HIV infection . Results : A total of 2413 people enrolled and contributed 9665 person-years of follow-up ( mean 4.0 years , maximum 6.9 years ) . The risk of HIV infection decreased as adherence improved , from 48.9 % overall to 83.5 % for those with at least 97.5 % adherence . In multivariable analysis , men were less adherent than women ( P = 0.006 ) and participants 20–29 years old ( P < 0.001 ) and 30–39 years old ( P = 0.01 ) were less adherent than older participants . Other factors associated with poor adherence included incarceration ( P = 0.02 ) and injecting methamphetamine ( P = 0.04 ) . Conclusion : In this HIV PrEP trial among people who inject drugs , improved adherence to daily tenofovir was associated with a lower risk of HIV infection . This is consistent with trials among MSM and HIV-discordant heterosexual couples and suggests that HIV PrEP can provide a high level of protection from HIV infection 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 . ) BACKGROUND Antiretroviral preexposure prophylaxis is a promising approach for preventing human immunodeficiency virus type 1 ( HIV-1 ) infection  in heterosexual population s. METHODS We conducted a r and omized trial of oral antiretroviral therapy for use as preexposure prophylaxis among HIV-1-serodiscordant heterosexual couples from Kenya and Ug and a. The HIV-1-seronegative partner in each couple was r and omly assigned to one of three study regimens -- once-daily tenofovir ( TDF ) , combination tenofovir-emtricitabine ( TDF-FTC ) , or matching placebo-- and followed monthly for up to 36 months . At enrollment , the HIV-1-seropositive partners were not eligible for antiretroviral therapy , according to national guidelines . All couples received st and ard HIV-1 treatment and prevention services . RESULTS We enrolled 4758 couples , of whom 4747 were followed : 1584 r and omly assigned to TDF , 1579 to TDF-FTC , and 1584 to placebo . For 62 % of the couples followed , the HIV-1-seronegative partner was male . Among HIV-1-seropositive participants , the median CD4 count was 495 cells per cubic millimeter ( interquartile range , 375 to 662 ) . A total of 82 HIV-1 infections occurred in seronegative participants during the study , 17 in the TDF group ( incidence , 0.65 per 100 person-years ) , 13 in the TDF-FTC group ( incidence , 0.50 per 100 person-years ) , and 52 in the placebo group ( incidence , 1.99 per 100 person-years ) , indicating a relative reduction of 67 % in the incidence of HIV-1 with TDF ( 95 % confidence interval [ CI ] , 44 to 81 ; P<0.001 ) and of 75 % with TDF-FTC ( 95 % CI , 55 to 87 ; P<0.001 ) . Protective effects of TDF-FTC and TDF alone against HIV-1 were not significantly different ( P=0.23 ) , and both study medications significantly reduced the HIV-1 incidence among both men and women . The rate of serious adverse events was similar across the study groups . Eight participants receiving active treatment were found to have been infected with HIV-1 at baseline , and among these eight , antiretroviral resistance developed in two during the study . CONCL 
    Output:
    
Specific barriers span individual and structural levels and include challenges to daily adherence , cost , and stigma .
Combining health services and long-acting PrEP formulas may facilitate better PrEP uptake and adherence .