Diagnostic accuracy of the Xpert CT/NG and OSOM Trichomonas Rapid assays for point-of-care STI testing among young women in South Africa: a cross-sectional study

Nigel Garrett, Nireshni Mitchev, Farzana Osman, Jessica Naidoo, Jienchi Dorward, Ravesh Singh, Hope Ngobese, Anne Rompalo, Koleka Mlisana, Adrian Mindel, Nigel Garrett, Nireshni Mitchev, Farzana Osman, Jessica Naidoo, Jienchi Dorward, Ravesh Singh, Hope Ngobese, Anne Rompalo, Koleka Mlisana, Adrian Mindel

Abstract

Objectives: Syndromic management of sexually transmitted infections (STIs) omits asymptomatic infections, particularly among women. Accurate point-of-care assays may improve STI care in low- and middle-income countries (LMICs). We aimed to evaluate the diagnostic performance of the Xpert Chlamydia trachomatis/Neisseria gonorrhoeae (CT/NG) and OSOM Trichomonas vaginalis (TV) Test as part of a STI care model for young women in South Africa.

Design: Diagnostic evaluation conducted as part of a prospective cohort study (CAPRISA 083) between May 2016 and January 2017.

Setting: One large public healthcare facility in central Durban, KwaZulu-Natal, South Africa PARTICIPANTS: 247 women, aged 18-40 years, attending for sexual and reproductive services to the clinic. Pregnant and HIV-positive women were excluded.

Outcomes: Diagnostic performance of the Xpert CT/NG and OSOM TV assays against the laboratory-based Anyplex II STI-7 Detection. All discordant results were further tested on the Fast Track Diagnostics (FTD) STD9 assay.

Results: We obtained vaginal swabs from 247 women and found 96.8% (239/247) concordance between Xpert and Anyplex for CT and 100% (247/247) for NG. All eight discrepant CT results were positive on Xpert, but negative on Anyplex. FTD STD9 confirmed three positive and five negative results, giving a confirmed prevalence of CT 15.0% (95% CI 10.5 to 19.4), NG 4.9% (2.2-7.5) and TV 3.2% (1.0-5.4). Sensitivity and specificity of Xpert CT/NG were 100% (100-100) and 97.6% (95.6-99.7) for CT and 100% (100-100) and 100% (100-100) for NG. The sensitivity and specificity of OSOM TV were 75.0% (45.0-100) and 100% (100-100).

Conclusion: The Xpert CT/NG showed high accuracy among young South African women and combined with the OSOM TV proved a useful tool in this high HIV/STI burden setting. Further implementation and cost-effectiveness studies are needed to assess the potential role of this assay for diagnostic STI testing in LMICs.

Trial registration number: NCT03407586; Pre-results.

Keywords: South Africa; Xpert CT/NG; point-of-care testing; sexually transmitted infections.

Conflict of interest statement

Competing interests: Cepheid Inc loaned two 4-module GeneXpert machines to the study team free-of-charge, but had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

© Author(s) (or their employer(s)) 2019. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

Figures

Figure 1
Figure 1
Study flow and results of the diagnostic evaluation of the Xpert CT/NG and Osom TV assays.

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