Background Daily and event-driven PrEP are both efficacious in preventing HIV infection. However, event-driven PrEP (edPrEP) is less well understood, in particular when provided as an alternative to daily PrEP. We studied regimen preferences and switches, and sexually transmitted infection (STI) incidence.
Methods We pooled data from the Dutch (AMPrEP) and the Belgian (Be-PrEP-ared) PrEP demonstration projects. In both projects, participants could choose between daily and event-driven PrEP (edPrEP) at 3-monthly study visits, when they were also screened for STIs including hepatitis C virus (HCV) infection. We assessed the proportion choosing each regimen, and the determinants of choosing edPrEP at baseline. Additionally, we compared the incidence rates (IRs) of HCV, syphilis, and chlamydia or gonorrhoea between regimens using Poisson regression.
Results The pooled dataset consisted of data of 571 men who have sex with men (n=374 AMPrEP; n=197 Be-PrEP-ared), of whom 148 (25.9%) chose edPrEP at baseline. Older participants (adjusted odds ratio (aOR)=1.38 per 10 year increase, 95% confidence interval (CI)=1.15–1.64) and those unemployed (aOR=1.68, 95%CI=1.03–1.75) were more likely to choose edPrEP at baseline. Median follow up was 26 months [interquartile range 21–27]. 381 participants (68.3%) never switched between PrEP regimens, 96 (17.2%) switched once, and 81 (14.5%) more than once. After 28 months, 23.5% used edPrEP. IR of HCV and syphilis did not differ between regimens, but the IR of chlamydia/gonorrhoea was higher among daily users (adjusted incidence rate ratio=1.61, 95%CI=1.35–1.94).
Conclusion A quarter of participants chose edPrEP at baseline and at 28 months this proportion was similar. The frequent switching suggests that participants adapt their PrEP regimen to their changing needs. Although the IR of HCV and syphilis were similar in both regimens, the lower incidence of chlamydia and gonorrhoea among edPrEP users may suggest that less frequent STI testing of this group could be considered.
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