Traeger MW et al. Association of HIV Preexposure Prophylaxis with Incidence of Sexually Transmitted Infections among Individuals at High Risk of HIV Infection. JAMA April 9, 2019;321(14):1380-90.

Gandhi M. Addressing the sexually transmitted infection and HIV syndemic. JAMA;321(14):1356.

Several studies have suggested that sexually transmitted infections (STIs) increase following initiation of preexposure prophylaxis (PrEP) for HIV.  This study from Australia included a cohort of gay and bisexual men from the Pre-exposure Prophylaxis Expanded (PrEPX) Study.  Included were participants who enrolled from July 2016 to April 2018.  All subjects received TDF/FTC for PrEP and underwent quarterly testing for HIV, chlamydia, gonorrhea, and syphilis. There were 2,981 men enrolled and data was available on 2892 (97%) at the final follow-up visit.

During a mean follow-up of 1.1 years there were 2928 STIs diagnosed among 1427 (48%) men including 1434 cases of chlamydia, 1242 gonorrhea, and 252 syphilis. The STI incidence was 92/100 person-years with only 25% of participants accounting for 76% of all STIs. Using a multivariable model, it was found that young age, greater number of anal sex partners, and participation in group sex were associated with increased risk of STI.  Inconsistent or no condom use was not significantly associated with STI risk.  Among 1378 participants with pre-enrollment STI testing data, incidence of infections increased from 69.5/100 person-years pre-study to 98/100 person-years during follow-up in this study.  However, after adjusting for testing frequency, the increase in incidence from 1-year pre-enrollment to follow-up was significant for any STI but the increase in incidence was attenuated to about 12%. The authors conclude that in this cohort of gay and bisexual men use of TDF/FTC for PrEP was associated with an increased incidence of STIs and they emphasize the need for frequent STI testing among patients who are taking PrEP for HIV prevention.

Commentary: I believe this is an important study that will help guide evolving evidence-based recommendations regard prescribing of PrEP and appropriate clinical protocols for monitoring patients who are taking PrEP. Distinguishing a true increased incidence of STIs due to behavior changes versus ascertainment bias from more frequent testing remains a key point of discussion and perhaps debate. Readers are strongly encouraged to look at this complete study along with the accompanying editorial by Dr. Monica Gandhi.