Is PrEP Associated with Higher Incidence of Sexually Transmitted Infections?

The roll-out of pre-exposure HIV infection prophylaxis (PrEP) has come with concerns about decreased condom use and subsequent increases in sexually transmitted infections (STIs) among PrEP users. After increased PrEP use among men who have sex with men (MSM) in Australia, investigators conducted a study to measure changes in HIV incidence and, as a secondary objective, changes in STI incidence.

Among 4275 participants enrolled between July 2016 and April 2018, 2981 had at least one postenrollment visit and were included in the analysis. Included participants were more likely to have used methamphetamines in the 3 months before enrollment. Their median age was 34, 40.7% had ever used postexposure prophylaxis (PEP), 28.5% were already on PrEP, and 13.7% were diagnosed with an STI at enrollment. During a median follow-up of 1.19 years, 2928 STIs were diagnosed among 48% of participants; 76% of all STIs occurred in 25% of participants. Incidence of an STI diagnosis during follow-up was 91.9 per 100 person-years, including incidences per 100 person-years of 45 for chlamydia, 39 for gonorrhea, and 8 for syphilis. Chlamydia and gonorrhea infections were most often rectal. Younger age, greater number of sex partners, and group sex participation were associated with greater risk for an STI. However, inconsistent or no condom use with casual partners was not significantly associated with STI risk. In an exploratory analysis of 1378 participants with at least one prestudy STI test, STI incidence increased from 69.5 per 100 person-years in the prestudy year to 98.4 per 100 person-years during the study (incidence rate ratio, 1.41). After adjustment for testing frequency, the difference was attenuated but still significant (adjusted IRR, 1.12).