CROI 2015As Truvada (tenofovir/emtricitabine) as pre-exposure prophylaxis (PrEP) use in San Francisco rises steadily, researchers have projected that further increases could take a significant bite out of the city’s already falling rate of new HIV cases, the National AIDS Treatment Advocacy Project (NATAP) reports. An increase in the proportion of people living with HIV who have a fully suppressed viral load thanks to antiretroviral treatment would also help lower the number of new HIV cases per year. Results were presented at the 2015 Conference on Retroviruses and Opportunistic Infections (CROI) in Seattle.

The researchers drew on data from San Francisco Department of Health surveillance, other recent HIV-related studies in the city, and published research on the likelihood of transmission based on an individual’s viral load and whether an infection is very recent. Information on PrEP was drawn from the iPrEx open-label extension trial, published in July 2014.

The researchers estimated that 16,089 San Francisco residents were good PrEP candidates. According to the National HIV Behavior Surveillance in San Francisco, 5,059 San Franciscans used PrEP over the past year.

In 2012, when few people used PrEP, there were 426 new HIV infections. This figure dropped to 359 in 2013. The researchers used a model that assumed two key variables: a 62 percent rate of viral suppression among the HIV-positive population (as is currently estimated to be the case); and that 65 percent of the highest-risk San Franciscans were taking Truvada (amounting to 4,000 person-years of PrEP use, a which essentially means that 4,000 people took the drug for one year, but which can account for some people only using Truvada for part of the year). They assumed that this scenario would yield about 350 new cases of HIV per year. If PrEP use were doubled to 8,000 person-years each year, the model projected that new annual cases would drop to 250, and to 200 with 12,000 person-years of PrEP use.

To read the NATAP report, click here.

To watch a webcast of the conference presentation, click here.