Seroepidemiological Characterization of a Syphilis Epidemic in the Republic of the Marshall Islands, Formerly a Yaws Endemic Area

The annual numbers of reported cases of syphilis in the Republic of the Marshall Islands (RMI) increased from none in 1983 to more than 600 in 1989, suggesting a large outbreak of syphilis. Much of the increase resulted from expanded serological screening. The apparent outbreak of syphilis, therefore, may have been partly the result of increased surveillance or, since the RMI was formerly a yaws endemic area, possibly due to a resurgence of yaws. To address this problem and better characterize the epidemic, we analysed results from a 1989/90 Ministry of Health Services mass serological screening on Majuro Atoll, the main population centre. Serum specimens from 9160 people (86% of residents aged 15–44 years) on Majuro were screened with the rapid plasma reagin (RPR) card test; we repeated the RPR and performed a confirmatory microhaemagglutination assay for Treponema pallidum-specific antibodies (MHA-TP) on a sample of serum specimens. To estimate the seroprevalence of syphilis, we also tested a sample of RPR nonreactive specimens by MHA-TP. Among people less than 45 years of age, total (11.5%) and high-titre (5.2%) seropositivity rates were highest in the 20–24 year age group, as was MHA-TP seroprevalence (15.9%). These results suggested that a large outbreak of syphilis was responsible for the observed seroreactivity. Cumulative incidence modelling and comparisons with the results of a previous serosurvey conducted in 1985 suggested that the duration of the syphilis epidemic was approximately 10 years and that incidence had not increased appreciably since 1985.