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  22nd Conference on Retroviruses and
Opportunistic Infections
Seattle Washington Feb 23 - 26, 2015
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Wider PrEP Use in San Francisco Could Cut New HIV Rate by 70%
  CROI 2015, February 23-26, 2015, Seattle, Washington
Mark Mascolini
New HIV infections in San Francisco could fall by 70% from 429 yearly in 2011 to about 125 yearly if about 14,000 city residents used preexposure prophylaxis (PrEP) yearly, according to a modeling study [1]. HIV incidence could fall even faster if viral suppression rates rise from a currently estimated 62% to 90% of people with HIV. But although PrEP use began to climb in San Francisco in 2013, PrEP uptake remains below one third the number needed to reach the 70% lower new-infection rate.
With its large gay population, San Francisco once led the United States in per capita HIV cases, but now the city leads in adopting prevention strategies, not limited to PrEP. Robert Grant, who led the first published placebo-controlled trial of PrEP in San Francisco and elsewhere,[2] noted that the city also sponsored routine HIV testing and pooled HIV RNA testing for high-risk people. As a result of these initiatives and grass-roots efforts, the San Francisco Department of Public Health estimates that 94% of HIV-positive city residents are diagnosed, up to 91% of those diagnosed start antiretroviral therapy, 88% of those in care reach a viral load below 200 copies, and 62% of all HIV-positive San Franciscans have attained viral suppression.
PrEP use began to climb in San Francisco in 2013 [3], 3 years after release of Grant's iPrEx results [2]. But no one has set PrEP targets for the city. With that goal in mind, Grant and colleagues devised a simple model to forecast HIV incidence with expanded PrEP in San Francisco. The model used data from San Francisco Department of Health surveillance, other recent San Francisco studies, published estimates of infectivity per partner, and rates of secondary infections during recent infection. Data on PrEP adherence, retention, and effectiveness came from iPrEx OLE, the open-label extension of the iPrEx trial [4].
Current PrEP use in San Francisco in 2014 ranged from 4% to 20% in three surveys of HIV-negative gay/bisexual men, Grant reported. A 2014 survey at the San Francisco AIDS Foundation sexually transmitted infection (STI) clinic found a current PrEP use rate of 16%, while 60% of clients said they definitely want PrEP from the clinic and 27% said they want PrEP but have questions about it. Current use at the clinic is about 27% of desired use (16% of 60%).
Grant estimated total eligible PrEP users in San Francisco at 16,089 by summing HIV-negative men at substantial risk, gay/bisexual men with an STI in the past year, female partners of HIV-positive MSM, and trans women. Of those 16,089 people, National HIV Behavior Surveillance in San Francisco counted 5059 PrEP users in the past year, or 31% of 16,089.
San Francisco reported 426 new HIV infections in 2012, when PrEP use was negligible. New infections fell to 359 in 2013, as PrEP use gradually rose. With a model based on a 62% overall viral suppression rate and 65% maximum PrEP uptake in the highest-risk strata, that rate reflects the model's prediction of 350 new cases per year at that point with a PrEP uptake of about 4000 person-years. The model projects that new HIV cases per year would fall to 250 with PrEP use of about 8000 person-years and to 200 with PrEP use of about 12,000 person-years--a tripling of the current use rate.
With a model based on a 62% viral suppression rate and 95% maximum PrEP uptake, the new-HIV rate falls to about 200 a year when PrEP use reaches about 8000 person-years. With 14,196 person-years of PrEP use, the new-HIV rate would fall 70% from before PrEP use in 2011. Grant noted that current PrEP use is 29% of what might be needed to cut new HIV infections by 70%.
If maximum PrEP uptake were 95%, as in the previous calculation, but the viral suppression rate rose from 62% to 90% of people with HIV, the impact on new HIV infections grows larger than seen in the previous calculation. For example, the new-HIV rate would fall to about 200 per year when PrEP use reaches 5000 person-years, rather than 8000 person-years in the previous calculation.
Grant concluded that PrEP use has climbed in San Francisco but has yet to reach one third of desired goals: 5095 PrEP starts versus 16,089 eligible candidates (32%), 4098 PrEP person-years of use versus an impact goal of 14,196 person-years (29%), and 16% current use versus 60% desired use in an STI clinic (27%).
These projections, Grant added, still do not include possible collateral benefits of PrEP, such as earlier HIV diagnosis and treatment, more STI testing, diagnosis, and treatment, and community mobilization. Other still-to-be-considered factors are immigration into and out of San Francisco, risk compensation with PrEP use (though risk compensation has not been observed in several populations), and heterosexual men (who account for 1% of San Francisco's HIV epidemic).
1. Grant RM, Albert Liu A, Jen Hecht J, et al. Scale-up of preexposure prophylaxis in San Francisco to impact HIV incidence. CROI 2015. February 23-26, 2015. Seattle, Washington. Abstract 25.
2. Grant RM, Lama JR, Anderson PL, et al. Preexposure chemoprophylaxis for HIV prevention in men who have sex with men. N Engl J Med. 2010;363:2587-2599. http://www.nejm.org/doi/full/10.1056/NEJMoa1011205
3. Liu A, Cohen S, Follansbee S, et al. Early experiences implementing pre-exposure prophylaxis (PrEP) for HIV prevention in San Francisco. PLoS Med. 2014;11:e1001613.
http://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1001613 4. Grant RM, Anderson PL, McMahan V, et al. Uptake of pre-exposure prophylaxis, sexual practices, and HIV incidence in men and transgender women who have sex with men: a cohort study. Lancet Infect Dis. 2014;14:820-829.