Sensitivity and specificity of typhoid fever rapid antibody tests for laboratory diagnosis at two sub-Saharan African sites

Abstract

OBJECTIVE: To evaluate three commercial typhoid rapid antibody tests for Salmonella Typhi antibodies in patients suspected of having typhoid fever in Mpumalanga, South Africa, and Moshi, United Republic of Tanzania. METHODS: The diagnostic accuracy of Cromotest® (semiquantitative slide agglutination and single tube Widal test),TUBEX®and Typhidot® was assessed against that of blood culture. Performance was modelled for scenarios with pretest probabilities of 5% and 50%. FINDINGS: In total 92 patients enrolled: 53 (57.6%) from South Africa and 39 (42.4%) from the United Republic of Tanzania. Salmonella Typhi was isolated from the blood of 28 (30.4%) patients. The semiquantitative slide agglutination and single-tube Widal tests had positive predictive values (PPVs) of 25.0% (95% confidence interval, CI: 0.6-80.6) and 20.0% (95% CI: 2.5-55.6), respectively. The newer typhoid rapid antibody tests had comparable PPVs: TUBEX®, 54.1% (95% CI: 36.9-70.5); Typhidot® IgM, 56.7% (95% CI: 37.4-74.5); and Typhidot® IgG, 54.3% (95% CI: 36.6-71.2). For a pretest probability of 5%, PPVs were: TUBEX®, 11.0% (95% CI: 6.6-17.9); Typhidot® IgM, 9.1% (95% CI: 5.8-14.0); and Typhidot® IgG, 11.0% (6.3-18.4). For a pretest probability of 50%, PPVs were: TUBEX®, 70.2% (95% CI: 57.3-80.5); Typhidot® IgM, 65.6% (95% CI: 54.0-75.6); and Typhidot® IgG, 70.0% (95% CI: 56.0-81.1). CONCLUSION: Semiquantitative slide agglutination and single-tube Widal tests performed poorly. TUBEX® and Typhidot® may be suitable when pretest probability is high and blood cultures are unavailable, but their performance does not justify deployment in routine care settings in sub-Saharan Africa.