The use of preexposure prophylaxis (PrEP) for HIV by men who have sex with men (MSM) is associated with increased rates of sexually transmitted infection (STI), researchers from Canada report.

"Physicians prescribing PrEP should probably emphasize, in a positive and non-judgmental way, that PrEP does not protect against other STIs and encourage regular STI screening even if patients are asymptomatic,” Dr. Vinh-Kim Nguyen from the University of Montreal reported

Some have expressed concerns that PrEP users' perception of decreased risk of HIV acquisition might lead them to engage in riskier sexual practices overall and increase their chances of acquiring STIs.

Dr. Nguyen and colleagues compared the incidence of Chlamydia trachomatis and Neisseria gonorrhea during the 12 months prior to and 12 months following the prescription of PrEP in their retrospective cohort study of 109 MSM receiving PrEP and 86 MSM receiving postexposure prophylaxis (PEP).

There were 83.5 STI cases per 100 patient-years during the year following PrEP prescription, compared with 48.6 cases per 100 patient-years in the year prior to PrEP, the team reports in AIDS.

During the 12 months following PrEP prescription, 30% of users contracted 1 STI, 12% contracted two STIs, and 9% contracted three or more STIs. By comparison, there were 38.4 STI cases per 100 patient-years among PEP users.

After adjusting for the increased frequency of screening visits after initiation of PrEP, the incidence of STI remained 39% higher after PrEP prescription. The 12-month risk of STIs was 2.18-fold higher among PrEP patients than among PEP controls, a significant difference.

Two patients in the PrEP group seroconverted to a positive HIV, including one who tested positive for HIV three months after discontinuing PrEP and one who was likely in a seroconversion window period at the time of PrEP prescription.

The researchers suggest that the increased rates of STI in the year following PrEP initiation indicate that patients may be engaging in higher-risk sex while on PrEP. “HIV prevention needs to be tailored to patients and always sensitive to changing sexual cultures in men who have sex with men,” Dr. Nguyen said.

Dr. Samuel M. Jenness reported, "Notably, the increased rates of STI testing, and presumably successful antibiotic treatment of diagnosed infections, for active PrEP users was insufficient to lower STI incidence. This is in contrast with projections from my recent study in Clinical Infectious Diseases, which suggest biannual testing associated with ongoing PrEP care could decrease STIs.”

One reason for the overall increase in infections in this new study may be the very high baseline levels of risk behavior before starting PrEP. With behavioral profiles like these, even small changes in risk after PrEP initiation could easily drive up STI rates. Testing 5 times a year, the average of study participants after starting PrEP, would be unlikely to mitigate the effects of that behavior.

PrEP provides a unique opportunity to address the sexual health and disease risks of gay and bisexual men. While PrEP does not biologically prevent bacterial STIs, as it does for HIV, PrEP users are recommended to get tested for STIs every 3-6 months with treatment if diagnosed.

Increased STI testing and treatment of high-risk men could provide important public health benefits, as men who are at substantial risk for HIV, and therefore indicated for PrEP, are also at risk for STIs through the same sexual partnership networks.

“To maximize public health benefits, PrEP should be used in combination with other effective HIV/STI prevention tools, including behavioral risk assessment and education, testing and treatment, and condoms with partners of unknown disease status.”