Background

HIV PrEP effectiveness is highly dependent on adherence. High STI incidence has been reported among PrEP users. We assessed the relationship between STI incidence (CT, NG, and syphilis) and PrEP adherence.

Methods

We performed a subanalysis of a controlled, open-label, two-arm, randomized clinical demonstration project of a text-message based adherence intervention. Participants had 48 weeks of follow-up and had STI testing every 12 or 24 weeks. PrEP adherence was measured at week 48 using intracellular tenofovir-diphosphate drug concentrations. We calculated incidence rate ratios for STIs among those adherent as compared with those not adherent to PrEP.

Results

Of the 381 assessed for CT, NG and syphilis at one or more follow-up visits, there were 16 cases of syphilis or 5.0 per 100 person years (95% CI: 2.6, 7.5); 63 cases of NG or 26.3 per 100 person years (95% CI: 19.8, 32.8); and 81 cases of CT or 36.3 per 100 person years (95% CI: 28.4, 44.2). We found no association between adequate PrEP adherence and STI incidence (aIRR: 0.97 95% CI: 0.67, 1.40).

Conclusions

We found that the incidence of STIs was not significantly different between those adherent to PrEP and those non-adherent. Further research is needed to assess how PrEP use may impact STIs over time.