New research in Clinical Infectious Diseases supports the use of preexposure prophylaxis (PrEP) to prevent HIV infection, as one of the first and largest published studies of PrEP in a clinical setting found no new cases of HIV among patients after initiation of PrEP.

Jonathan Volk, MD, MPH, physician and epidemiologist at Kaiser Permanente San Francisco Medical Center, and colleagues followed 657 patients who initiated PrEP treatment over a 32-month observation period. The average age of participants was 37 and 99% were men who have sex with men (MSM). Participants were asked about changes in behavior after six months of PrEP treatment, of which the number of sexual partners was unchanged in 74% of patients, decreased in 15%, and increased in 11%. Condom use was unchanged in 56% of patients, decreased in 41%, and increased in 3%.

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Thirty percent had been diagnosed with at least one sexually transmitted infection (STI) at six months after PrEP initiation; at 12 months, 50% had been diagnosed with any STI, 33% had a rectal STI, 33% had chlamydia, 28% had gonorrhea, and 5.5% had syphilis. It is notable that no new HIV infections were diagnosed among the patients; however, because there was no control group, the researchers do not know if the reported STI rates would have been greater compared to patients not taking PrEP.

The authors concluded that this evidence suggests that PrEP could prevent new HIV infections, even in a high-risk setting. Previous evidence had only supported the efficacy of PrEP from clinical trials and a demonstration project.

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