Comparative performance of stool antigen and serum antibody assays relative to stool culture among patients with suspected typhoid fever in Cape Coast, Ghana

Abstract

Typhoid fever remains a major public health challenge in low- and middle-income countries, where limited laboratory infrastructure often necessitates reliance on rapid diagnostic tests (RDT). The serum antibody assay is the most commonly used RDT for diagnosing typhoid fever in Ghana; however, its reliability is limited. This study aimed to evaluate the diagnostic performance of rapid stool antigen and serum antibody tests for typhoid fever, using stool culture as the reference standard. A comparative cross-sectional study was conducted among 208 clinically suspected typhoid fever patients. Stool samples were cultured for the detection of presumptive Salmonella isolates consistent with S. Typhi and tested with EvanCare rapid stool antigen kits, while serum samples were tested using the JusChek Typhidot antibody test kit. Sensitivity and specificity were analyzed in comparison with stool culture. Paired differences in sensitivity and specificity were assessed using McNemar’s test, with corresponding 95% confidence intervals. Agreement between the paired rapid tests was assessed using Cohen’s kappa. Stool culture identified 43 participants as positive and 165 as negative. Among culture-positive participants, the stool antigen test had a sensitivity of 86.0%, compared with 76.7% for the serum antibody test, corresponding to a difference of 9.3% points (95% CI: −6.62–24.92; p  = 0.388). Among culture-negative participants, specificity was 95.2% for the stool antigen test and 90.3% for the serum antibody test, corresponding to a difference of 4.9% points (95% CI: −0.25–10.33; p  = 0.096). There was no statistically significant difference between the assays in either culture-positive or culture-negative participants. The stool antigen test demonstrated higher sensitivity and specificity than the serum antibody test; however, the differences were not statistically significant. Although the point estimates favoured the stool antigen test, the findings do not provide sufficient evidence to conclude that it is superior to the serum antibody assay. The stool antigen test may nevertheless provide a useful rapid diagnostic option in settings where timely typhoid testing is required, while confirmatory culture remains important where feasible.