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PrEP Initiation Associated With Increased STI Incidence Among Gay, Bisexual Men


A study of gay and bisexual men found that incidence of sexually transmitted infections (STIs) increased following pre-exposure prophylaxis (PrEP) initiation.

Amidst emerging evidence suggesting that the risk of sexually transmitted infections (STIs) increases among gay and bisexual men following initiation of pre-exposure prophylaxis (PrEP) due to behavior changes, a new study is adding to the literature, finding that starting PrEP after study enrollment was associated with an increased incidence of STIs compared with pre-enrollment.

The study of nearly 3000 people at risk for HIV found that there was an STI incidence of 91.9 per 100 person-years among gay and bisexual males, underscoring the importance of frequent STI testing among the patient population.

“STI incidence increased from before to after commencing PrEP with the increase greatest for chlamydia infection,” wrote the researchers. Throughout the study period, 2928 STIs were diagnosed among 1427 (48%) participants, which included 1434 chlamydia diagnoses, 1242 gonorrhea diagnoses, and 252 syphilis diagnoses. There were incidences of 45 per 100 person-years for chlamydia, 39 per 100 person-years for gonorrhea, and 8 per 100 person-years for syphilis.

The number of STIs per participant ranged from 0 to 12, and multiple infections were diagnosed in 736 (25%) participants, which accounted for 76% of all infections during the period. Characteristics linked to greater risk of STI diagnosis included higher numbers of anal sex partners and participation in group sex. However, the researchers noted that in the multivariable analysis, there was no independent association with reported levels of condom use, which is typically associated with STI risk.

Participants were enrolled between July 26, 2016, and April 1, 2018, in Australian Collaboration for Coordinated Enhanced Sentinel Surveillance clinics across Victoria, Australia. They received PrEP prescriptions at enrollment and during quarterly study visits, where they also completed a sexual behavior questionnaire and underwent HIV and STI testing.

Among the patients, there were 1378 who had at least 1 STI test prior to study enrollment. The researchers found that for these patients, incidence of an STI increased from 69.5 per 100 person-years in the year prior to enrollment to 98.4 per 100 person-years during the follow-up period.

PrEP use prior to enrollment was reported in 541 of these participants. Compared with PrEP-naïve participants, prior PrEP users were more likely to exhibit risk-based behaviors at enrollment. These patients were also significantly more likely to have STI incidence in the year prior to enrollment compared with PrEP-naïve patients (92.4 per 100 person-years vs 55.1 per 100 person-years).

However, STI incidence significantly increased to 94.2 per 100 person-years among PrEP-naïve patients during follow-up whereas PrEP-experienced participants saw a nonsignificant increase to 104.1 per 100 person-years.

Consistent with findings from the entire study cohort, PrEP-naïve patients saw the biggest increase in chlamydia incidence, followed by gonorrhea incidence. Meanwhile, there was no significant change in syphilis incidence.

However, the news isn’t all bad. The researchers explained: “A recent modeling study found that while PrEP use may lead to increased STI incidence following individual-level behavior change, the timely diagnosis and short duration of STIs among PrEP users due to high screening frequency may lead to an overall decrease in STI prevalence and incidence among the wider gay and bisexual male population.”


Traeger M, Cornelisse V, Asselin J, et al. Association of HIV preexposure prophylaxis with incidence of sexually-transmitted infections aming individuals at high risk of HIV infection [published online April 9, 2019]. JAMA. doi: 10.1001/jama.2019.2947.

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