Syphilis serology and HIV infection in Harare, Zimbabwe

Objective: To determine the reliability of serological tests in detecting s yphilis in a factory worker cohort and examine the impact of concurrent HIV infection on serolagical tests for syphilis. Method: Reactions to non-treponemal and treponemal antigens were tested usi ng sera from a cohort of 34101 factory workers in Harare, Zimbabwe. The par ticipants consented to regular testing for syphilis, by VDRL, and HIV using two ELISAs. All sera from men who were VDRL positive, and a random sample of VDRL negative sera, were tested by RPR, TPHA, and where appropriate FTA- Abs. From the results,men were defined as having no syphilis, active syphil is, incident syphilis, historic syphilis, or giving biological false positi ve reactions. Results: 709 sera were examined from 580 men. There were 78 cases of active syphilis in the cohort, giving a prevalence of 2.3%, and the seroincidence was 0.25 per 100 person years of follow up. The prevalence of HIV in the c ohort was 19.8%. There was a strong association between syphilis, whether a ctive, incident or historic, and I-IN seropositivity. With both I-IN positi ve and negative sera the negative predictive values of VDRL and RPR were >9 9.9% while the positive predictive value for VDRL (30%) was lower than for RPR (39%). Biological false positive reactions were detected in 0.5% of the cohort, with in most cases a transient rise in VDRL titres up to <1/16. Hi gher false positive titres occurred in five men, each of whom was HIV posit ive. Conclusions: The VDRL is reliable in detecting possible cases of syphilis e ven in a community with a high prevalence of heterosexually transmitted HIV . There is need, however, for confirmatory tests. The prevalence of syphili s in this cohort is very low in comparison with other countries in southern Africa, but is consistent with recent data from Harare. Despite a strong a ssociation between syphilis and HIV it was clear that syphilis could not be counted as a major factor fuelling the HIV epidemic in Zimbabwe.