Syphilis in heterosexual women: case characteristics and risk factors for recent syphilis infection in Tokyo, Japan, 2017–2018

Abstract

In response to an increase in heterosexual syphilis notifications in Tokyo, we conducted a questionnaire-based case–control study among women aged ≥20 years and sexually active in the past six months who sought a syphilis test in Tokyo during 2017–2018. Cases were women diagnosed as recent syphilis infection based on serological tests. Controls were serologically non-reactive or those with only a past syphilis infection. We described cases and assessed for risk factors of recent syphilis using logistic regression. A total of 524 women (60 cases, 464 controls) were enrolled. Notably, among cases, 10 (16.7%) were students, 3 (5.0%) had a history of syphilis, and 14 (23.3%) had a single sex partner in the past six months. Female sex worker (FSW) status was strongly associated with syphilis (odds ratio [OR] = 3.40; 95% confidence interval [CI] = 1.96–5.90). In multivariable analysis, recent syphilis was associated with inconsistent condom use for vaginal/anal sex among FSWs (adjusted OR [aOR] = 3.42; 95%CI = 0.92–12.70) and among non-FSWs, with younger age (aOR = 0.36; 95%CI = 0.19–0.70; increase per category from 20–24, 25–29 to ≥30 years) and ≤high school education (aOR = 5.24; 95%CI = 1.95–14.10). A notable proportion of cases were those with first time infection and those with only a single partner. Moreover, risk factors differed between FSWs and non-FSWs, and a multi-pronged approach to prevent syphilis is required.

Social and structural determinants associated with the prevalence of sexually transmitted infections among female commercial sex workers in Dhaka City, Bangladesh

“…Abstinence from heterosexual anal intercourse ( Table 3 ) is 97% less likely (AOR = .03, P<0.001) to be associated with STIs. Previous studies also reported similar findings [ 15 , 17 , 31 , 52 ]. Anal sex enhances HIV/STIs among FCSWs, riskier than heterosexual vaginal intercourse for lower condom usage [ 17 , 27 , 31 , 52 ]; accelerated further with condom-less sex and improper lubricant use behaviors [ 17 , 27 , 52 ].…”

“…Previous studies also reported similar findings [ 15 , 17 , 31 , 52 ]. Anal sex enhances HIV/STIs among FCSWs, riskier than heterosexual vaginal intercourse for lower condom usage [ 17 , 27 , 31 , 52 ]; accelerated further with condom-less sex and improper lubricant use behaviors [ 17 , 27 , 52 ]. Female sex workers practice anal sex because of intimacy/poverty/coercion/peer pressure and lack of knowledge/perception of the exacerbated risk of anal sex for HIV/STI transmission [ 27 ].…”

“…This study elucidated ( Table 3 ) that inconsistent/condom-less sex was 7.7 times (inverting AOR = .13, P<0.001) riskier for inflicting STIs and aligns with most studies [ 14 , 16 , 17 , 49 , 53 ]. Studies in Bangladesh also reported inconsistent/condomless sex as a high-risk factor for a new STI case among FCSWs [ 6 , 26 ].…”

“…In this study, various individual risk factors ( Table 2 ) influence STIs profoundly; similar results are also found in other research [ 38 , 44 ]. Young (<30 years) sex worker was 43%-72% less likely to be afflicted with STIs (P = .031) than aged one, which may be due to unprotected sex by older FCSWs or protected encounters by younger [ 17 , 20 , 47 ]. However, risky sex by under-aged/unmarried FCSWs is also reported [ 12 , 48 ].…”

Increased cervical Chlamydia trachomatis and syphilis infections in Japanese females of reproductive age in the late 2010s: Possible cause

“…From 2017 to 2018, the risk factors for syphilis in Japanese female patients were investigated; a history of working in the sex industry within the past six months was identified as one such factor (odds ratio = 3.40; 95% confidence interval = 1.96-5.90) [17]. This suggests visits by foreign tourists to Japanese sex businesses might be responsible for the rise in syphilis cases.…”