Background Substantial increases in syphilis have been reported since the early 2000s in northern countries, particularly among men who have sex with men (MSM). The authors aimed to identify risk factors for early syphilis in MSM in Lille, a large urban area of northern France.

Methods A matched case–control study was conducted in MSM aged ≥18 years. Cases were diagnosed with primary, secondary or early latent syphilis between April 2008 and June 2010. Controls sought care in STIs clinics or were followed in an HIV clinic. Controls had no history of and no current syphilis. They were matched to cases for age and HIV status. Multivariate conditional logistic regression models were used to identify risk factors for early syphilis.

Results 53 patients with early syphilis were enrolled. Average age was 37 years, and 47% were HIV-infected. For analysis, they were matched to 90 controls. Factors associated with syphilis were: low educational attainment (OR=5.38, 95% CI 1.94 to 14.94; p=0.001), receptive oral sex with casual male partners without a condom (OR=4.86, 95% CI 1.63 to 14.48; p=0.005) and anal sex toy use with casual male partners (OR=2.72, 95% CI 1.01 to 7.32; p=0.05). Seeking of sex partners online (OR=5.17, 95% CI 1.33 to 20.11), use of poppers (OR=2.2, 95% CI 1.1 to 4.3) and erectile dysfunction drugs (OR=1.9, 95% CI 1.0 to 13.2) were associated with syphilis only in the univariate analysis.

Conclusions Receptive oral sex without a condom and use of anal sex toys were identified as presenting a major risk of syphilis infection. Although these practices have been shown to present low risk of HIV transmission, the general public is unaware of their impact on transmission of other STIs.