SAN FRANCISCO, Sept. 3 (UPI) -- A large Kaiser Permanente study in San Francisco among people at high risk for HIV found none of them contracted it while using preexposure prophylaxis, or PrEP, a two-drug combination designed to prevent the disease's spread.
PrEP is a combination of the drugs emtricitabine and tenofovir, sold as the drug Truvada, meant to prevent an HIV infection from being permanent. Ideally, the preventative treatment is part of a safe sex regimen that uses condoms to protect against the spread of disease.
"Our study is the first to extend the understanding of the use of PrEP in a real-world setting and suggests that the treatment may prevent new HIV infections even in a high-risk setting," said Dr. Jonathan Volk, a physician and epidemiologist at Kaiser Permanente San Francisco Medical Center, in a press release. "Until now, evidence supporting the efficacy of PrEP to prevent HIV infection had come from clinical trials and a demonstration project."
Kaiser Permanente is a private health insurer with its own affiliated hospitals, medical centers and pharmacies operating in eight states and the District of Columbia.
The San Francisco study was conducted over the course of 2 1/2 years with 657 people who had an average age of 37, almost all of whom were gay men. The average length of time participants used the pill-a-day preventative treatment was 7.2 months.
After 6 months of using PrEP, 143 patients were surveyed about behavioral changes, because the drug is meant to be part of safe sex, not negate the use of condoms. Researchers found that 74 percent of participants had no change in their number of sexual partners, 15 percent decreased the number, and 11 percent reported an increase.
Condom use among participants remained the same for 56 percent of the participants, however 41 percent reported using them less often and just 3 percent said they'd used them more often.
Over the course of the study, none of the participants contracted HIV. Six months into the study, however, 30 percent of participants had been diagnosed with at least one sexually transmitted infection, or STI. At 12 months, 50 percent had been diagnosed with at least one -- 33 percent had a rectal STI, 33 percent had chlamydia, 28 percent had gonorrhea, and 5.5 percent had syphilis.
Researchers report they did not have a control group testing for STI infection. Despite being unsure if there is a connection between PrEP use and incidence of STIs, they recommend testing for the infections as part of any PrEP program.
"This is very reassuring data," Volk told the New York Times. "It tells us that PrEP works even in a high-risk population."
The study is published in Clinical Infectious Diseases.