Introduction Dual HIV/syphilis rapid diagnostic tests (RDTs) may prevent congenital syphilis by facilitating syphilis diagnosis in pregnant women receiving HIV testing. The dual HIV-1/2 treponemal syphilis RDT (Chembio DPP HIV-Syphilis Assay) performs well in the lab, but its field performance is unknown. We investigated test performance under field conditions for this dual RDT and Malawi’s single RDTs for HIV and syphilis to assess whether the dual RDT might be a suitable substitute for the first-line single RDT in Malawi’s HIV algorithm.
Methods During Jul 2014−Nov 2015, 1798 pregnant women attending a first antenatal visit were recruited if their HIV status was negative or unknown. Women received the single HIV (Determine HIV-1/2) and syphilis (Determine Syphilis TP) RDTs and the dual RDT. By Dec 2016, CDC had performed Rapid Plasma Reagin (RPR), Treponema pallidum particle agglutination (TPPA), and 3rd-generation HIV EIA testing with Western Blot confirmation. In Jan 2017, the validity of all RDTs relative to the CDC HIV algorithm, TPPA, and TPPA/RPR results were calculated.
Results Of 1791 women (99.6%) with complete results, 258 (14.4%) were HIV-positive by CDC’s algorithm; 81 (4.5%) were TPPA+; and 46 (2.6%) were TPPA+/RPR+. The dual RDT was 95.0% sensitive and 96.0% specific for HIV; the single HIV RDT was 93.0% sensitive and 99.3% specific. HIV test specificities were significantly different (p<0.01). Both dual and single HIV RDTs were 96.9% sensitive during repeat lab testing. Using TPPA+ as the standard, the dual RDT was 69.1% sensitive and 99.8% specific for syphilis; the single syphilis RDT was 63.0% sensitive and 99.8% specific. Among women most likely to vertically transmit syphilis (TPPA+/RPR+, titer ≥1:4), the dual and single RDTs were 100.0% and 88.2% sensitive, respectively.
Conclusion The dual RDT syphilis component performed comparably to the single syphilis RDT and performed very well among women likely to vertically transmit syphilis. The dual RDT HIV component had comparable sensitivity but lower specificity than the single HIV RDT.
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