Incidence and Risk Factors for Early Syphilis Among Men Who Have Sex With Men in Australia, 2013–2019: A Retrospective Cohort Study

Abstract

Background We aimed to examine the incidence of syphilis in men who have sex with men (MSM) and identify subgroups of MSM at a higher risk of syphilis infection. Methods We conducted a retrospective cohort study of MSM attending a sexual health clinic in Australia during 2013–2019, who had at least two syphilis serological tests during the study period. The incidence of syphilis was expressed as per 100 person-years. A cox regression analysis was conducted to identify risk factors for syphilis. Results A total of 24,391 individual MSM (75,086 consultations) were included. 1,404 new syphilis cases were diagnosed with an incidence of 3.7/100 person-years (95%CI:3.5–3.9). Syphilis incidence was higher in MSM living with HIV (9.3/100 person-years) than in MSM taking HIV pre-exposure prophylaxis (PrEP) (6.9/100 person-years) or HIV-negative MSM not taking PrEP (2.2/100 person-years). Risk factors associated with high incidence of syphilis included: MSM living with HIV (adjusted hazard ratio [aHR]:2.7), MSM taking HIV PrEP (aHR:2.1), past history of syphilis infection (aHR:2.4), injecting drug use (aHR:2.7), condomless anal sex (aHR:1.7), >4 sexual partners in the last 12 months (aHR:1.2), and concurrent STI (chlamydia and gonorrhoea) (aHR:1.6). Conclusion The incidence of syphilis remains high among MSM, particularly in subgroups with associated risk factors for syphilis infections. These data highlight the need for biomedical and behavioural interventions to be targeted to subgroups of MSM at the highest risk of syphilis infection.

Incidence, risk factors, and clinical findings of syphilis among men living with HIV in Croatia during the COVID-19 pandemic

“…The overall incidence rate of syphilis in our men living with HIV was 6.0/100 PYFU and the annual incidence rate ranged from 3.3/100 PYFU in 2018 to 9.3/100 PYFU in 2021. Similarly, to our findings in 2021, a retrospective cohort study from Australia reported an incidence of early syphilis of 9.3 per 100 person-years in MSM living with HIV in the period 2013–2019 22 . Another study from Thailand found an incidence of syphilis of 10.2 per 100 person-years in a predominantly MSM cohort diagnosed with acute HIV infection in the period April 2009 through December 2018 23 .…”

Increasing incidence of syphilis among men living with HIV in Croatia during the COVID-19 years 2020 and 2021

“…The overall incidence rate of syphilis in our men living with HIV was 6.0/100 PYFU and the annual incidence rate ranged from 3.3/100 PYFU in 2018 to 9.3/100 PYFU in 2021. Similarly, to our ndings in 2021, a retrospective cohort study from Australia reported an incidence of early syphilis of 9.3 per 100 person-years in MSM living with HIV in the period 2013-2019 [22]. Another study from Thailand found an incidence of syphilis of 10.2 per 100 person-years in a predominantly MSM cohort diagnosed with acute HIV infection in the period April 2009 through December 2018 [23].…”

“…Risk factors associated with syphilis such as being MSM and having a history of previous syphilis have also been reported previously [22,23,27,[40][41][42][43]. Younger age was also associated with syphilis; however, this relationship was not as strong as in other studies [40,43].…”

Response to the ASHM 2023 statement on the use of doxy‐PEP in Australia: considerations and recommendations

“…For instance, multivariate analysis estimated that GBMSM with concurrent gonococcal or chlamydial infection had a 60% higher risk of syphilis compared with GBMSM without gonococcal or chlamydial infection. 25 Given the likelihood that gonococcal infections are frequently exposed to doxy-PEP, this potentially undermines gonococcal antimicrobial stewardship efforts by accelerating the spread of gonococcal AMR 26 and potentially selecting for multidrug-resistant gonococcal strains. 27 By averting gonorrhoea infection, the doxy-PEP study reduced ceftriaxone use by half in the doxy-PEP arm against a background of 20% N. gonorrhoeae tetracycline resistance at the time of the trial.…”

“…However, STI co‐infection frequently occurs. For instance, multivariate analysis estimated that GBMSM with concurrent gonococcal or chlamydial infection had a 60% higher risk of syphilis compared with GBMSM without gonococcal or chlamydial infection 25 . Given the likelihood that gonococcal infections are frequently exposed to doxy‐PEP, this potentially undermines gonococcal antimicrobial stewardship efforts by accelerating the spread of gonococcal AMR 26 and potentially selecting for multidrug‐resistant gonococcal strains 27 .…”