Risk of sexually transmitted infections among U.S. military service members in the setting of HIV pre-exposure prophylaxis use

by Jason M. Blaylock, Evan C. Ewers, Elizabeth J. Bianchi, David B. King, Rosemary O. Casimier, Hector Erazo, Stephen Grieco, Jenny Lay, Sheila A. Peel, Kayvon Modjarrad, Charmagne G. Beckett, Jason F. Okulicz, Paul T. Scott, Shilpa Hakre

The evidence for an increased incidence of sexually transmitted infections (STIs) among patients utilizing HIV pre-exposure prophylaxis (PrEP) has been inconsistent. We assessed the risk of incident STI while on PrEP compared to periods off PrEP among military service members starting PrEP.

Incidence rates of chlamydia, gonorrhea, syphilis, hepatitis C virus, and HIV were determined among military service members without HIV prescribed daily oral tenofovir disoproxil fumarate and emtricitabine for HIV PrEP from February 1, 2014 through June 10, 2016. Hazard ratios for incident STIs were calculated using an Anderson-Gill recurrent event proportional hazard regression model.

Among 755 male service members, 477 (63%) were diagnosed with incident STIs (overall incidence 21.4 per 100 person-years). Male service members had a significantly lower risk of any STIs (adjusted hazard ratio (aHR) 0.21, 95% CI 0.11–0.40) while using PrEP compared to periods off PrEP after adjustment for socio-demographic characteristics, reasons for initiating PrEP, surveillance period prior to PrEP initiation, and the effect of PrEP on site and type of infection in multivariate analysis. However, when stratifying for anatomical site and type of infection, the risk of extragenital gonorrhea infection (pharyngeal NG: aHR 1.84, 95% CI 0.82–4.13, p = 0.30; rectal NG: aHR 1.23, 95% CI 0.60–2.51, p = 1.00) and extragenital CT infection (pharyngeal CT: aHR 2.30, 95% CI 0.46–11.46, p = 0.81; rectal CT: aHR 1.36, 95% CI 0.81–2.31, p = 0.66) was greater on PrEP compared to off PrEP although these values did not reach statistical significance.

The data suggest entry into PrEP care reduced the overall risk of STIs following adjustment for anatomical site of STI and treatment. Service members engaged in PrEP services also receive more STI prevention counseling, which might contribute to decreases in STI risk while on PrEP.