In Japan, notifications of syphilis have been increasing similar to North America in recent years. Men who have sex with men (MSM) in Tokyo contributed a large proportion of the notifications. We thus conducted a prospective case-control study in Tokyo to assess potential risk factors for incident syphilis among MSM.
MSM who attended Shirakaba Clinic, a facility in Tokyo that targets sexual minority populations, were recruited during April to November 2015. Participants were required to have been sexually active in the past 6 months. Cases were seropositive for primary, secondary or asymptomatic syphilis at clinic visit and seronegative at prior visit; patients seronegative but with oral ulcers positive for Treponema pallidum DNA (polA/TpN47 PCR) at clinic visit were also considered as cases. For each case, two controls seronegative at clinic visit were selected. Using logistic regression, odds ratios (ORs) and 95% confidence intervals (CIs) were estimated to assess potential risk factors for incident syphilis.
Among 35 cases and 71 controls, the median age was 37 years (range 21-63) and age of first sex with another male was 18 (9-30) years, similar between cases and controls. In univariate analysis, past history of syphilis, number of sex partners in the past 6 months (1-5, 6-15 and ≥16), average frequency of anal/oral sex (1/month, ≥1/month but < 1/week and ≥1/week), alcohol intake during anal/oral sex, sex toy use, inconsistent condom use during anal sex and Tokyo residency were positively associated with syphilis while HIV seropositivity was negatively associated. In multivariate analysis, Tokyo residency (OR=3.4, 95% CI 1.0 -12.0), average frequency of anal/oral sex (OR=2.5, 95% CI 1.2-5.3; increase per category), inconsistent condom use during anal sex (OR=2.9, 95% CI 1.1-7.7) and HIV seropositivity (OR=0.2, 95% CI 0.1-0.8) remained associated with syphilis.
This is the first study of risk factors for incident syphilis among MSM in Japan. Frequency of sex and inconsistent condom use during anal sex were associated with incident syphilis. Further investigation to evaluate the relationship between incident syphilis and HIV seropositivity and Tokyo residency is needed.
I. Itoda, None
T. Takahashi, None
T. Yamagishi, None
T. Matsui, None
T. Sunagawa, None
M. Ohnishi, None
K. Oishi, None
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