Risk factors for syphilis infection among pregnant women: results of a case-control study in Shenzhen, China

Background: China has been experiencing a rapidly growing syphilis epidemic since the early 1990s, with the reported incidence of congenital syphilis increasing from 0.01 cases per 100 000 live births in 1991 to 19.7 cases per 100 000 live births in 2005. Detailed studies of risk factors for syphilis in pregnant women are needed to inform new preventive interventions. Objective: To investigate factors associated with recent syphilis infection among pregnant women and recommend strategies for improved preventive interventions in the community. Methods: A case-control study was conducted among women attending antenatal clinics in Shenzhen City, South China. Cases were antenatal clinic women testing positive for early syphilis, based on laboratory results, with those testing negative being controls. All participants completed the same anonymous questionnaire covering demographics, lifestyle, sexual behaviour, and sexual partnerships. Results: 129 cases and 345 controls were recruited. Syphilis was significantly associated with unmarried status, less education, multiple sex partners, travel of sex partner in the past 12 months, a history of induced abortion, and previous sexually transmitted infections. Overall, there were no differences between syphilis-positive and negative women in household registration status (hukou), living district and duration in Shenzhen, monthly income, and age at first sex. Conclusions: Many demographic and behavioural risk factors are associated with syphilis among pregnant women. In the government congenital syphilis control programme, comprehensive preventive interventions should be provided in all clinical settings in addition to the current procedures for syphilis screening among antenatal women.