Increasing trend of syphilis and infection resistance: a retrospective study.

To assess the epidemic trends of syphilis and to investigate syphilis infections after exposure to infectious patients.A total of 17 211 syphilis patients from the period January 1999 to September 2012 were enrolled in this study. A variety of syphilis prevalence measures were evaluated. We analyzed the characteristics of 2954 cases using available information. Of these patients, 535 early syphilis cases were identified as index patients and the status of their sexual partners was monitored. All sexual partners were followed for 6 months to 1 year through serological testing and clinical examinations.The proportion of syphilis-positive clients at the sexually transmitted disease (STD) clinic increased annually, with a five-fold increase from 1999 to 2011 (from 6.1% to 30.0%). The highest increase in syphilis infection occurred among patients in the 20-29 years age group. Male and female cases increased at the same rate between 1999 and 2007, but female cases increased at a greater rate than male cases from 2008 to 2012. Of the 535 sexual partners in the study, 330 (61.7%) were infected with syphilis and 205 (38.3%) were seronegative without any symptoms. Gender may influence disease infection rates (p=0.008), but not at different stages of early syphilis.There was an increasing trend of syphilis infection in Hefei, China. A proportion of highly exposed individuals could be resistant to syphilis infection.