Performance of Widal IgM/IgG rapid diagnostic tests, and stool culture in identifying asymptomatic typhoid infections

Test performance of Widal, IgM/IgG RDT, and stool culture for typhoid diagnosis

Abstract

Background: Introduction: Non-febrile asymptomatic persons present a unique case definition for typhoid since the only means of diagnosi is the detection of typhoidal antigens or antibodies or the growth of Salmonella bacteria in cultures. However, in recent times, the diagnostic capacities of commonly used testing regimes have been called into question.
Objective: The study examined the test characteristics of three testing regimes, Widal, IgM/IgG Rapid Diagnostic test, and stool culture tests in the diagnosis of typhoid fever among non-febrile asymptomatic persons.
Methods: The cross-sectional study sampled healthy persons in Atebubu Municipality. Blood and stool samples were collected from each participant after they consented to the study and completed a sociodemographic questionnaire. Participants’ sera were tested for antibodies against Salmonella “O” and “H” antigens, and the presence of IgM and IgG against Salmonella antigens. Stool samples were cultured on Salmonella-Shigella agar, and the characteristic colonies of Salmonella spp. identified. The degree of agreement between different tests and standard tests was analysed by calculating Cohen’s kappa statistic.
Results: Eighty-three (83) study participants were studied. The diagnostic tests evaluated in this study vary significantly in their performance metrics. While immunological tests such as IgM and IgG show promise in detecting typhoid fever, they also present challenges in specificity and agreement with culture methods. The Widal test, despite its high specificity, has low sensitivity, limiting its usefulness for accurate diagnosis of typhoid fever. The IgM test demonstrated high sensitivity (89.3%) but low specificity (32.7%), suggesting its effectiveness in detecting true cases while exhibiting a considerable rate of false positives. Conversely, the IgG test showed lower sensitivity (50.0%) but higher specificity (65.5%), indicating better utility in ruling out non-cases. Notably, extended culture incubation (48hrs) significantly increased test sensitivity rates compared to 24hr cultures.
Conclusion: Complementary testing regimens should be adapted to increase diagnostic accuracy in typhoid fever, especially among non febrile, asymptomatic patients.