BackgroundAt the individual level, higher HIV viral load predicts sexual transmission risk. We evaluated San Francisco's community viral load (CVL) as a population level marker of HIV transmission risk. We hypothesized that the decrease in CVL in San Francisco from 2004–2008, corresponding with increased rates of HIV testing, antiretroviral therapy (ART) coverage and effectiveness, and population-level virologic suppression, would be associated with a reduction in new HIV infections.Methodology/Principal FindingsWe used San Francisco's HIV/AIDS surveillance system to examine the trends in CVL. Mean CVL was calculated as the mean of the most recent viral load of all reported HIV-positive individuals in a particular community. Total CVL was defined as the sum of the most recent viral loads of all HIV-positive individuals in a particular community. We used Poisson models with robust standard errors to assess the relationships between the mean and total CVL and the primary outcome: annual numbers of newly diagnosed HIV cases. Both mean and total CVL decreased from 2004–2008 and were accompanied by decreases in new HIV diagnoses from 798 (2004) to 434 (2008). The mean (p = 0.003) and total CVL (p = 0.002) were significantly associated with new HIV cases from 2004–2008.Conclusions/SignificanceReductions in CVL are associated with decreased HIV infections. Results suggest that wide-scale ART could reduce HIV transmission at the population level. Because CVL is temporally upstream of new HIV infections, jurisdictions should consider adding CVL to routine HIV surveillance to track the epidemic, allocate resources, and to evaluate the effectiveness of HIV prevention and treatment efforts.

The Soweto Men’s Study assessed HIV prevalence and associated risk factors among MSM in Soweto, South Africa. Using respondent driven sampling (RDS) recruitment methods, we recruited 378 MSM (including 15 seeds) over 30 weeks in 2008. All results were adjusted for RDS sampling design. Overall HIV prevalence was estimated at 13.2% (95% confidence interval 12.4–13.9%), with 33.9% among gay-identified men, 6.4% among bisexual-identified men, and 10.1% among straight-identified MSM. In multivariable analysis, HIV infection was associated with being older than 25 (adjusted odds ratio (AOR) 3.8, 95% CI 3.2–4.6), gay self-identification (AOR 2.3, 95% CI 1.8–3.0), monthly income less than ZAR500 (AOR 1.4, 95% CI 1.2–1.7), purchasing alcohol or drugs in exchange for sex with another man (AOR 3.9, 95% CI 3.2–4.7), reporting any URAI (AOR 4.4, 95% CI 3.5–5.7), reporting between six and nine partners in the prior 6 months (AOR 5.7, 95% CI 4.0–8.2), circumcision, (AOR 0.2, 95% CI 0.1–0.2), a regular female partner (AOR 0.2, 95% CI 0.2–0.3), smoking marijuana in the last 6 months (AOR 0.6, 95% CI 0.5–0.8), unprotected vaginal intercourse in the last 6 months (AOR 0.5, 95% CI 0.4–0.6), and STI symptoms in the last year (AOR 0.7, 95% CI 0.5–0.8). The results of the Soweto Men’s Study confirm that MSM are at high risk for HIV infection, with gay men at highest risk. HIV prevention and treatment for MSM are urgently needed.