P173 Sexually transmitted infection diagnoses among HIV pre-exposure prophylaxis users largely explained by partner numbers and testing frequency

Abstract

<h3>Background</h3> There are conflicting data on the impact of increasing HIV Pre-exposure prophylaxis (PrEP) use on transmission and diagnosis of other sexually transmitted infections (STI) such as syphilis, gonorrhoea and chlamydia infection. We used observational data from German HIV/STI checkpoints on visits of PrEP users and non-users in 2019 and 2020 to analyse determinants for STI diagnosis. <h3>Methods</h3> Checkpoint clients fill out an online questionnaire at each visit. Demographic and behavioural data of the online questionnaire are linked to laboratory results. We analysed data of client-subgroups with relevant PrEP use (at least 1% of visits in the group by people using PrEP) for determinants of STI diagnoses using univariate and multivariate logistic regression models. PrEP use was categorized as never; intended; former; on demand, and regular. <h3>Results</h3> Data from 12,235 checkpoint visits including blood testing and 10,131 checkpoint visits including additional swab-testing for gonorrhoea and chlamydia could be included in the analysis. Active syphilis was diagnosed 2–3 times more frequently in visits of PrEP users compared to visits of non-users, gonorrhoea and/or chlamydia was diagnosed in 20% of PrEP user visits and 12% of non-PrEP-user visits. Three of four regular PrEP users had last been checked for STI within the last 3 months, but only one of nine non-PrEP-users. The number of sex partners and condomless sex partners was higher for PrEP users than for non-PrEP-users. In multivariate regression models, number of sex partners, number of condomless sex partners, and recency of STI testing explained the probability of STI diagnosis, the type of PrEP use was not significant. <h3>Conclusions</h3> Differences regarding STI diagnoses between PrEP users and non-users are largely explained by partner numbers and testing frequency. Due to the cross-sectional nature of our data we cannot determine whether initiating PrEP leads to higher partner numbers and/or reduced condom use.