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 5and 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(95confidence interval; CI: 0.6-80.6) and 20.0(95CI: 2.5-55.6); respectively. The newer typhoid rapid antibody tests had comparable PPVs: TUBEX; 54.1(95CI: 36.9-70.5); Typhidot IgM; 56.7(95CI: 37.4-74.5); and Typhidot IgG; 54.3(95CI: 36.6-71.2). For a pretest probability of 5; PPVs were: TUBEX; 11.0(95CI: 6.6-17.9); Typhidot IgM; 9.1(95CI: 5.8-14.0); and Typhidot IgG; 11.0(6.3-18.4). For a pretest probability of 50; PPVs were: TUBEX; 70.2(95CI: 57.3-80.5); Typhidot IgM; 65.6(95CI: 54.0-75.6); and Typhidot IgG; 70.0(95CI: 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