Background Bacterial sexually transmitted infections (STI) are rising among men-who-have-sex-with-men (MSM) in many urban settings. Western Sydney Sexual Health Centre (WSSHC) provides HIV/STI services for a culturally and linguistically diverse MSM population; many have commenced HIV pre-exposure prophylaxis (PrEP) since 2016. The study analyses changes in the incidence of chlamydia, gonorrhoea and syphilis among this MSM population around a period of transition to PrEP provision.

Methods Data were extracted from WSSHC’s Specialised Health Information Program database for men providing anorectal/oropharyngeal samples for chlamydia/gonorrhoea testing during two time periods (2013–2015, ‘pre-PrEP era’; 2016–2018, ‘PrEP era’). Extracted variables included age at visit, country of birth, STI diagnosis date and site of chlamydia/gonorrhoea infection. Analyses used population-average panel-data models based on generalised estimation equations (5% cut-off level of error, p=0.05). Logistical regression analyses accounted for the number of clinic visits; a multivariate model adjusted for age group, year and PrEP use.

Results Data were extracted for 6,734 STI testing visits by 2,796 MSM. There were 1,121 (16.7%) gonorrhoea cases, 1,144 (17.0%) chlamydia cases and 257 syphilis cases (199 with early syphilis). Chlamydia (OR:1.08; 95%CI:1.04–1.13) and gonorrhoea incidence (OR:1.06; 95%CI:1.02–1.11) increased over time; syphilis incidence did not. There was no significant trend differences in bacterial STI incidence by country of birth. In multivariate analyses, the incidence of chlamydial and gonococcal cases was much higher among PrEP users: any chlamydial infection (aOR:2.35; 95%CI 1.96–2.81), anorectal chlamydia (aOR:2.60; 95%CI 1.93–3.52), any gonorrhoea (aOR:2.13; 95%CI 1.65–2.76), anorectal gonorrhoea (aOR:2.00; 95%CI 1.38–2.90). There were no significant differences in syphilis incidence between PrEP users and non-PrEP users.

Conclusion Incident chlamydial and gonococcal infections, but not syphilis, significantly increased over time in MSM attending WSSHC and PrEP use was the major determinant of these observations. Data analyses at clinic level are important for informing local health service planning and health promotion activities.

Disclosure No significant relationships.