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Study Finds Increase in STIs After Starting PrEP

Although once daily pre-exposure prophylaxis (PrEP) prevents up to 99% of HIV transmission risk, gay and bisexual men taking PrEP are 72% more likely to acquire a sexually transmitted infection (STI) than they were before starting PrEP according to study data released last month in the journal AIDS.

The study was conducted among 195 gay and bisexual men who regularly attend an LGBTQ health clinic in Montreal, Canada. Clinicians found that the rate of anal chlamydia infection alone more than doubled during the year after starting PrEP compared to the prior year. The rates of gonorrhea and syphilis increased, too, but to a less significant degree.

During the yearlong study, 30% of PrEP users acquired one STI, 12% acquired two STIs, and 9% acquired three or more STIs. The study also found that PrEP users were significantly more likely to acquire an STI than those taking post-exposure prophylaxis (PEP).

Since the U.S. Food and Drug Administration (FDA) approved PrEP for HIV prevention in 2012, opponents have argued that the medication would result in more sexual risk taking. Vinh-Kim Nguyen, the lead author of the study and HIV physician-anthropologist, emphasized the need for more research to understand the effects of PrEP on sexual networks, sexual culture, and STI transmission.

“We need to understand that as our portfolio of HIV prevention options expands, we must be attentive to unintended or unforeseen consequences,” said Nguyen, who pointed out how PrEP is already changing sexual cultures. “Witness the now common disclosure of PrEP use in dating apps, etc.”

Unlike previous studies that only measured STI rates of individuals after they began PrEP, this is the first study to compare rates of STI incidence both before and after individuals started PrEP. By establishing a baseline STI rate before study participants began PrEP, researchers were able to establish that PrEP is likely the cause of the increased rate of STIs. Long-term studies are required to determine whether this increased risk persists beyond the first year on PrEP.

Other factors could possibly account for the increase in STI rates in this study population. For example, before PrEP became widely available, yearly surveys by the U.S. Centers for Disease Control (CDC) found that rates of condomless anal intercourse had increased steadily among gay and bisexual men from 39% in 2001 to 60% in 2014. Given the rise in condomless anal sex before the introduction of PrEP, it is therefore likely that STI risk has been increasing in this population for over a decade.

Study authors hypothesized that the higher rate of STIs after starting PrEP may be due to “risk compensation,” in which individuals engage in higher risk sex due to the perceived protection due to PrEP. Because PrEP may be lowering men’s sexual inhibitions and leading to higher rates of STIs, this study underscores the importance of STI testing and counseling for PrEP patients every three months.