Background Reflecting worldwide trends, an outbreak of infectious syphilis was declared in Winnipeg, Canada in 2012. Initially exclusively an outbreak amongst men who have sex with men (MSM), increases among women were observed in 2014/15. This study compared the characteristics of more recent heterosexual cases of syphilis to those at the start of the heterosexual outbreak.
Methods Data were from infectious syphilis investigations (September 1st, 2011 to August 31st, 2018) from Winnipeg, Canada. Age-standardized rates (2006 Canadian population standard) and 95% confidence intervals (95%CI) are reported. Bivariate analyses (χ 2 tests) and multivariable logistic regression models compared heterosexual cases from 2011/12-2014/15 to 2015/16-2017/18 cases on socio-demographic characteristics and risk factors. Adjusted odds ratios (AOR) and 95%CI are reported.
Results A total of 770 infectious syphilis cases were reported to public health. Rates increased 25-fold, from 1.6/100,000 persons (95%CI:0.8–2.9) to 40.5/100,000 persons (95%CI: 36.1–45.3), between 2011/12 and 2017/18. The proportion of women increased from 8% to 47%; correspondingly, the ratio between male and female rates decreased from 4.5 to 1.3. Amongst men, the heterosexual proportion increased from 9% in 2011/12 to 75% in 2017/18. In bivariate analyses, more recent heterosexual cases were younger (p<0.001); more likely to report crystal methamphetamine (CM) use (30% vs 3%, p<0.001); gonorrhea (21% vs 3%, p<0.001) and chlamydia co-infection (23% vs 10%, p=0.004); history of incarceration (36% vs 14%, p<0.001); and having no fixed address (15% vs 2%, p<0.001). In multivariable models, CM use (AOR: 7.9; 95%CI:2.4–26.7), gonorrhea co-infection (AOR: 7.1; 95%CI: 2.1–24.1), and history of incarceration (AOR: 1.8; 95%CI: 1.1–3.5) remained statistically significant.
Conclusion At least two parallel epidemics of syphilis are occurring in Winnipeg. Although MSM cases have declined, control of the heterosexual outbreak remains elusive. Populations with multiple vulnerabilities, including CM use and history of incarceration bear the greatest burden. Public health surveillance should remain vigilant for congenital syphilis.
Disclosure No significant relationships.
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