What's Up With PrEP and STIs?

Project Inform July 14, 2017
  • Critics have been warning since the concept of oral PrEP was in its infancy that it would lead to major increases in condomless sex among users and a corresponding dramatic spike in sexually transmitted infections (STIs). So far, the data have been inconclusive.

    A journal article last year by one of the U.S.'s largest PrEP clinics at Kaiser Permanente of Northern California did find significant increases in STIs after initiation of PrEP in nearly 1,000 recipients. Formal demonstration projects, efficacy studies and even some cohorts have either reported no increases, however, or mixed results. A presentation at the Conference on Retroviruses and Opportunistic Infections (CROI) 2017 in Seattle, Washington, found similarly mixed results.

    To investigate this issue, the STI and HIV program in King County, which includes Seattle, looked at data from gay men enrolling in the county PrEP program between September 2014 and June 2016. Condom use was evaluated at PrEP initiation, and then at 3, 6 and 9 months later. STI trends were measured by looking at diagnoses one year before starting PrEP, at PrEP start, and then during the time a person was on PrEP.

  • Though 218 people started PrEP, complete 9-month data were available for only 108. The cohort was relatively young -- on average 30 years old -- and while just over half were white, 22% were Hispanic, 10% were Asian or Pacific Islander, 9% were black and 2% were Native American.

    The percentage of those saying that they never used condoms for receptive anal sex nearly doubled after starting PrEP but remained below 10% at all time points. Thus, reports of condomless receptive anal sex did increase, which has been reported more consistently. With STI rates, however, it was a more mixed and confusing picture.

    Part of the confusion is that number of STI diagnoses increased substantially in the three months before starting PrEP -- on average the rates almost tripled for all diseases, including chlamydia, gonorrhea and syphilis. This makes the case quite strongly that those for whom PrEP will be most appropriate are those who seek it out or who are offered it.

    What is less clear, however, is how to interpret STI diagnosis after starting PrEP. While chlamydia (in general) and rectal chlamydia did increase from 16% to 22% and 15% to 19% respectively over the study period, diagnosis of gonorrhea and rectal gonorrhea stayed the same and early and early-latent syphilis decreased by nearly half.

    While these data will certainly not convince PrEP critics that the intervention is being promoted dangerously, they do offer a more sober and less sensational view than an analysis of STI data from PrEP studies published as a commentary in the journal AIDS not long before CROI. The authors there claimed that STI rates were more than 10x higher in PrEP users than non- users across several studies or cohort reports, a finding that garnered substantial headlines, social media traffic and press releases from a notoriously anti-PrEP HIV organization in the US.

    A rebuttal published in AIDS on March 13, 2017, pointed out serious flaws in the earlier analysis and came to the conclusion that while STI rates were higher (about three times higher) in PrEP-users vs. non-users in the same set of studies, this much smaller difference means that the influence of PrEP on STIs is nearly impossible to separate from other confounding factors, including escalating STI rates going back more than a decade in MSM, more frequent STI testing in those on PrEP than those not, and the reality that those most likely to become infected with an STI are also those most likely to seek out PrEP in the first place.


    MA Montano, et al. Changes in sexual behaviour and STI diagnoses among MSM using PrEP in Seattle, WA. 2017 CROI, Seattle. Abstract 979.

    Harawa NT, et al. Serious concerns regarding a meta-analysis of preexposure prophylaxis use and STI acquisition. AIDS. 2017 Mar 13;31(5):739-740.

Bridging the Gap: HIV PrEP Watch Demetre Daskalakis, M.D.