Field performance of a rapid point-of-care diagnostic test for antenatal syphilis screening in the Amazon region, Brazil

Abstract

We evaluated an immunochromatographic point-of-care (POC) syphilis test in 712 pregnant women under field conditions in remote communities of the Amazon region (Brazil), and identified risk factors for syphilis. Women were screened by POC test using whole blood obtained by fingerprick, the fluorescent treponemal antibody absorption (FTA-Abs) test as the gold standard and the Venereal Diseases Research Laboratory (VDRL) test to determine test performance in active syphilis. Multivariate analysis was conducted to identify factors associated with syphilis infection. Among women, 2.2% had syphilis (positive FTA-Abs) and 0.8% active syphilis (FTA-Abs and VDRL positive). In all, 2.2% of samples were positive by the POC test. The sensitivity, specificity, positive and negative predictive values were 62.5% (95% confidence interval [CI]: 38.6–81.5), 99.1% (95% CI: 98.1–99.6), 62.5% (95% CI: 38.6–81.5) and 99.1% (95% CI: 98.1–99.6), respectively. The POC test identified 62.5% (10/16) of syphilis cases, 66.7% (4/6) of active syphilis cases and all high-titre syphilis cases (VDRL > 1:8). Older age was associated with syphilis infection. The rapid test performed moderately well as a screening tool for low-risk populations. This combined with on-site testing and same day treatment could expand antenatal syphilis screening programmes in distant communities characterized by difficult access to antenatal services and infrequent clinical follow-up visits.