HIV pre-exposure prophylaxis and diagnoses of sexually transmitted infections - observational data from German checkpoints, 01/2019-08/2021.

Background: The impact of starting HIV pre-exposure prophylaxis (PrEP) on diagnoses of sexually transmitted infections (STI) remains unclear. We used data from German HIV/STI Checkpoints collected from 01/2019 to 08/2021 to determine the impact of PrEP use on syphilis, gonorrhoea and chlamydia diagnoses.

Methods: We used self-reported data on demographics, sexual behaviour, testing and PrEP use, as well as lab-confirmed diagnoses from visits to HIV/STI Checkpoints in Germany. PrEP use was categorized as (1) never used; (2) intention to use; (3) former use; (4) current on-demand use; (5) daily use. In multivariate regression analyses (MRA) with gonorrhoea, chlamydia, and syphilis diagnoses as outcomes, we controlled for age, number of sexual partners, number of condomless anal intercourse (CAI) partners in the last six months, and testing recency.

Results: For the analysis, we included 9,219 visits for gonorrhoea and chlamydia testing and 11,199 visits for syphilis testing conducted at checkpoints from 01/2019 to 08/2021. MRA identified age (aOR 0.98; 95%CI 0.97-0.99), number of sexual partners in the past six months (aOR 4.90; 95%CI 2.53-9.52 for 11 + partners), and use of chemsex substances (aOR 1.62; 95%CI 1.32-2.00) as risk factors for gonorrhoea, while age (aOR 0.99; 95%CI 0.98-1.00), number of CAI partners (aOR 3.19; 95%CI 2.32-4.41 for 5 + partners), partner sorting (aOR 1.30; 95%CI 1.09-1.54), and use of chemsex substances (aOR 1.29; 95%CI 1.05-1.59) were risk factors for chlamydia infections. For syphilis, the number of CAI partners (aOR 3.19; 95%CI 1.60-6.34 for 5 + partners) was found to be the only significant risk factor. There was a strong association between PrEP use and the number of sexual partners (≤ 5 vs.>5: aOR 3.58; 95%CI 2.15-5.97 for daily PrEP use), the number of CAI partners in the past six months (≤ 1 vs.>1: aOR 3.70; 95%CI 2.15-6.37 for daily PrEP use), and the number of STI tests performed (suggesting higher testing frequency). Both outcomes were also related to partner sorting, chemsex, and selling sex.

Conclusions: Checkpoint visits reporting current PrEP use or intention to start PrEP correlated with eligibility criteria for PrEP, i.e. high partner numbers, inconsistent condom use during anal intercourse, and use of chemsex drugs. Use of HIV-specific prevention methods such as HIV serosorting, PrEP sorting, and viral load sorting was reported more frequently. (Daily) PrEP use was an independent risk factor for a chlamydia diagnosis only.