Syphilitic seroreactivity among the Thai population aged 50 years and above: value of mass screening

The present study is concerned with the evaluation of routine serologic screening for syphilis among the general population aged 50 and above living in a suburban area of Bangkok, Thailand. Among 941 subjects aged 50 years and above recruited in a cohort study named the CERB study, blood of 798 subjects was obtained and their sera were tested for syphilis using the passive particle agglutination test for detection of antibodies to Treponema pallidum (TPPA) and the rapid plasma reagin (RPR). Of 798 subjects, 132 (16.5%) were reactive to serum TPPA. Their mean age (standard deviation) was 61.4 (8.4) years. Fifty-six subjects (42.4%) were male. Prevalence of syphilitic seroreactivity increased with age (p = 0.004). Prevalence of syphilitic seroreactivity among male and female subjects was 18.3% and 15.4% respectively (p = 0.001). Prevalence of syphilitic seroreactivity among subjects with formal education (14.4%) was significantly lower than that among subjects without formal education (26.5%) (p = 0.001). Of 132 subjects, 10 (7.6%) had and a rapid plasma reagin (RPR) titer of 1:16 or higher. None of them reported symptoms of primary or secondary syphilis during the initial survey. Of 125 subjects who were interviewed in depth during the revisit survey, 24 subjects had known about their syphilitic infection prior to this study. Among these 24 subjects, 4 had not received any treatment for syphilis and 1 used herbal medicine. Therefore, 106 subjects (84.4%) were untreated or inadequately treated. These findings suggest the value of mass screening for syphilis among the Thai population aged 50 years and above.