Utility of the Determine™ Syphilis TP Rapid Test in Commercial Sex Venues in Peru

Abstract

Objectives: This study sought to evaluate the utility of the Determine™ Syphilis TP test performed in Peruvian commercial sex venues for the detection of active syphilis; and determine the feasibility of integrating rapid syphilis testing for female sex workers (FSW) into existing health outreach services.

Methods: We tested 3,586 female sex workers for syphilis by Determine™ in the field using whole blood fingerstick, and by RPR and TPHA in a central laboratory in Lima using sera.

Results: 97.4% of the FSW offered rapid syphilis testing participated; and among those who tested positive, 87% visited the local health center for treatment. More than twice as many specimens were RPR reactive using serum in Lima (5.7%) than tested positive by whole blood Determine™ in the field (2.8%), and although most were confirmed by TPHA, only a small proportion (0.7%) were RPR reactive at ≥1:8 dilutions, and likely indicating active syphilis. Sensitivity, specificity and PPV of the Determine™ Syphilis TP test in whole blood when compared to serum RPR reactivity at any dilution confirmed by TPHA as the gold standard were 39.3%, 99.2% and 71.4% respectively. Sensitivity improved to 64.0% when using serum RPR ≥1:8 confirmed by TPHA. Invalid tests were rare (0.3%).

Conclusions: Rapid syphilis testing in sex work venues proved feasible, but Determine™ using whole blood obtained by fingerstick was substantially less sensitive than reported in previous laboratory-based studies using serum. Although easy to perform in outreach venues, the utility of this rapid syphilis test was relatively low in settings where a large proportion of the targeted population has been previously tested and treated.