Pre-Exposure Prophylaxis for HIV and the Risk of Symptomatic and Asymptomatic Sexually Transmitted Infections

Pre-exposure prophylaxis (PrEP) is an additional effective strategy for the prevention of HIV in high-risk individuals. Some concerns have been raised on the potential increase in the incidence of risky sexual behaviours and sexually transmitted infections (STIs) in PrEP-users. Additionally, there is an ongoing discussion on the need for systematic STI screening in PrEP users and on the role of doxycycline post-exposure prophylaxis (doxyPEP). We aimed at evaluating the incidence and predictive factors of symptomatic and asymptomatic STIs in PrEP users. This retrospective observational study conducted at the primary sexual health centre in Turin (Ce.Mu.S.S.) involves individuals who started PrEP between the 1st of June 2021 and the 31st of May 2023. The included follow-up comprises planned and unplanned visits until the 31st of May 2024. Participants included were those that fulfilled the criteria for the prescription of PrEP according to guidelines. Individuals who never presented to a planned or unplanned follow-up visit were excluded. The total number of episodes with symptomatic and asymptomatic STIs was calculated and normalized by the number of visits per patient. Variables were described using average (± standard deviation) and compared through standard parametric tests (Chi-square, Fisher’s, t-test and ANOVA). 551 PrEP users were included in this study, 545 (98.9%) were men having sex with men. The average age of the participants was 39 years (±9). 77.3% of individuals chose on-demand PrEP while 22.7% chose daily PrEP. After an average follow-up of 15.3 months (±8.63), 283 (51.36%) participants had at least one STI during the follow-up period and 164 (29.76%) had more than one STI. 237 participants (43.02%) reported at least one asymptomatic STI, and 115 (20.90%) reported at least one symptomatic STI. The percentage of visits with symptomatic and asymptomatic STIs were 4.91 (± 10.97) and 11.23 (± 15.34), respectively. Daily PrEP users had higher rates of asymptomatic STIs per patient (0.92 vs. 0.56, p=0.003), probably reflecting the stricter follow-up. Both symptomatic and asymptomatic STIs were more prevalent in PrEP users who started in 2021 (0.95 vs. 0.65 vs. 0.43, p=0.002), possibly reflecting a longer followup time or a selection of higher-risk subgroups when PrEP was less popular among the MSM community. Higher risk score at the preliminary visit were associated with higher rates of STIs during follow-up (Rho=0.197, p<0.001). Visits where PrEP users reported higher rates of condom use for anal intercourse were associated with lower rates of STI diagnoses (rho=-0.104, p=0.037 at T1; rho= -0.114, p=0.035 at T2). Individuals who were addressed to PrEP by a health care professional and not spontaneously were more likely to report higher condom use at the 2 second (+25.21% for versatile, +31.08% for insertive and +36.42% for receptive anal intercourses) and fourth (+21.27% for versatile anal intercourses) follow-up visits. Participants born abroad had a similar pattern of protetcion, reporting more condom usage at the third (+26.64% for receptive anal intercourses) and fourth (+34.86% for receptive anal intercourses) follow-up visit. This study confirms the high prevalence of STIs in PrEP users and highlights the importance of counselling for PrEP users, and possibly tailoring counselling for specific subgroups at higher risk of STIs. New strategies for STIs prevention need to be studied in high-risk persons