Evidence of changing sexual behaviours and clinical attendance patterns, alongside increasing diagnoses of STIs in MSM and TPSM

Background: Due to rising numbers of STI diagnosis and increasing prevalence of anti-microbial resistance, we explored trends in STI testing frequency and diagnoses, alongside sexual decision-making and attitudes concerning condom use and HIV pre-exposure prophylaxis (PrEP) at a large urban UK sexual health clinic.
Methods: We examined 66,528 electronic patient records (EPR) covering 40,321 attendees between 2016-2019; 3,977 of whom were men or trans-persons-who-have-sex-with-men (MSM/TPSM). We also explored responses from MSM/TPSM attendees sent an electronic questionnaire between November 2018-2019 (n=1,975) examining behaviours/attitudes towards PrEP. We measured trends in STI diagnoses and sexual behaviours including condomless anal intercourse (CAI), utilising linear and logistic regression analyses.
Results: Tests resulting in gonorrhoea, chlamydia or syphilis diagnoses increased among MSM/TPSM from 13.5%-18.5% between 2016-2019 (p<0.001). The average MSM/TPSM STI testing frequency increased from 1.5/person/year to 2.1/person/year (p=0.017). Gay MSM/TPSM had the highest proportions of attendances resulting in diagnoses, increasing from 15.1%-19.6% between 2016-2019 (p<0.001) compared to bisexual/other MSM/TPSM increasing from 6.9%-14.5% (p<0.001); alongside smaller but significant increases in non-MSM/TPSM from 5.9-7.7% (p<0.001). The proportion of MSM/TPSM clinic attendees reporting CAI in the previous 3 months prior to at least one appointment in a given year increased significantly from 40.6%-45.5% between 2016-2019 (p<0.0001) and average number of partners from 3.8-4.5 (p=0.002). Of 617 eligible questionnaire responses, 339/578 (58.7%) HIV-negative and 29/39 (74.4%) HIV-positive MSM/TPSM indicated they would be more likely to have CAI with someone on PrEP versus not on PrEP. 358/578 (61.9%) HIV-negative respondents said that PrEP use would make them more likely to have CAI with HIV-negative partners.
Conclusion: Rising numbers of STI diagnoses amongst MSM/TPSM are not attributable to increased testing alone. Increased CAI and number of partners may be attributable to evolving sexual decision-making among PrEP users and their partners. Proportionally, bisexual/other MSM/TPSM have the steepest increase in STI diagnoses.