Incidence of syphilis reinfection and associated risk factors among gay, bisexual and other men who have sex with men in England, 2017-2021

Introduction

Syphilis infection can cause significant morbidity and increases the likelihood of acquiring and transmitting HIV. Gay, bisexual and other men who have sex with men (GBMSM) have disproportionately high diagnosis rates of syphilis compared to heterosexuals. To inform interventions to prevent syphilis reinfection in GBMSM, we need a greater understanding of the incidence of and risk factors for syphilis reinfection among this population.

Methods

We determined the incidence of syphilis reinfection among GBMSM attending sexual health services with at least one prior syphilis diagnosis (any stage) in GUMCAD STI Surveillance System between 2017–2021. A zero-inflated Poisson model was used to identify factors associated with syphilis reinfection using incidence rate-ratios with 95% confidence intervals.

Results

Between January 2017-December 2021, a total of 27,677 GBMSM were diagnosed at least once with syphilis; the median age was 36 years (IQR 29–46) and 74% were of White ethnicity. 2,737 (9.9%) GBMSM had at least one reinfection, and the incidence of reinfection was 6.22 (95%CI: 6.00–6.44) per 100 person-years. The risk of reinfection was higher among GBMSM living with HIV (1.82[1.69–1.96]) and those who had a previous chlamydia or gonorrhoea diagnosis (1.22[1.12–1.34]). Reinfection risk varied by region of residence and, compared to UK-born GBMSM, risk was highest among those born in Central (1.43[1.01–2.02]) or South America (1.20[1.04–1.37]). No difference in reinfection risk was observed by age group, ethnicity or deprivation quintile.

Discussion

The incidence of syphilis reinfection in GBMSM was 6% but this varied by region of residence, region of birth, HIV status and bacterial STI history. These findings can be used to inform which GBMSM should be prioritised in strategies to prevent syphilis reinfection, including biomedical interventions such as doxycycline post-exposure prophylaxis.