Identifying Subgroups At Higher Risk Of Infectious Syphilis In Major Australian Cities: Analysis Of National Sentinel Surveillance Data 2011-2018

Background In Australia, infectious syphilis notifications have increased 234% in the past decade, from 1318 in 2008 to 4398 in 2017. Although historically concentrated among urban men who have sex with men and remote Indigenous communities, a rise in syphilis notifications among women in major cities and cases of congenital syphilis have been observed. We analysed trends in infectious syphilis positivity among women and heterosexual men in major Australian cities and identified associated risk factors. Methods De-identified patient data were extracted from 34 sexual health clinics within a national sentinel surveillance network (2011–18). All women and heterosexual men ≥ 15 years in major cities were included. Infectious syphilis positivity was defined as the proportion of attendees per 6-monthly calendar period with recorded syphilis testing who had recorded clinical diagnoses of infectious syphilis. Poisson regression determined annual trends in positivity and risk factors for infectious syphilis (rate ratios and 95% CIs). Results Of 100,230 patients attending the clinics, 50.8% were female (of whom, 96.1% were of childbearing age), 51.2% were aged 15–29 years, 1.7% were Indigenous and 7.4% were from culturally and linguistically diverse (CALD) backgrounds. Modelled positivity for infectious syphilis (2011–18) increased 85% in females from 2.41 (95%CI:1.67–3.14) to 4.48 (95%CI:3.53–5.43) per 1000 patients tested, and 76% in heterosexual males from 4.47 (95%CI:3.44–5.49) to 7.87 (95%CI:6.49–9.24). Factors associated with increased risk of infectious syphilis included: reporting a history of injecting drug use (RR:4.36;95%CI:3.26–5.83), using condoms inconsistently in the past year (RR:2.30;95%CI;1.10–4.79), being male (RR:1.80;95%CI:1.51–2.14), Indigenous (RR:1.70;95%CI:1.02–2.84), from CALD backgrounds (RR:1.90;95%CI:1.46–2.46), and older (30–39 years: RR:1.33;95%CI:1.08–1.65; 40–49 years: RR:2.95;95%CI:2.34–3.73; 50+ years:RR:3.59;95%CI:2.81–4.57). Lower risk was observed in bisexual females (RR:0.53;95%CI:0.30–0.94) and female sex workers (RR:0.43;95%CI:0.29–0.63). Conclusion Increasing syphilis in women and heterosexual men in major Australian cities requires enhanced prevention, including integration of sexual and reproductive health care into harm reduction programs.