Diagnostic efficacy of Widal slide agglutination test against Widal tube agglutination test in enteric fever

Introduction: Enteric fever is an endemic disease in India and warrants rapid and affordable diagnosis. The Widal slide agglutination test is a commonly used rapid screening test for this purpose. The literature available on its diagnostic ability in comparison to the tube agglutination test is however scanty. Hence, this study aims to evaluate the efficacy of the Widal slide agglutination test and the tube agglutination test for the diagnosis of enteric fever. Materials and Methods: A total of 1470 sera were collected during the study period of one year from patients having pyrexia of unknown origin. All the samples were tested for the presence of anti O and anti H agglutinins against S. typhi and S. paratyphi A by semi quantitative slide and quantitative tube agglutination tests as per standard protocols. The titers of 1:80 (O agglutinins) and 1:160 (H agglutinins) were taken as the significant titer for the diagnosis of enteric fever. The results of the slide agglutination test were compared with the tube agglutination test and analyzed using Fisher’s exact test. The sensitivity, specificity, positive and negative predictive values of slide agglutination were calculated using the tube agglutination method as a standard for comparison. Results: Of the 294 slide positive samples, 209 (71.1%) samples tested negative by the tube agglutination test. The sensitivity, specificity, positive and negative predictive values for the slide agglutination test were observed to be 100 % (CI 95.75-100%), 84.91% (CI 82.93-86.73%), 28.91% (CI 23.84-34.45%) and 100% (CI 99.69-100%) respectively. Conclusion: Serological diagnosis of enteric fever should always be confirmed by the tube agglutination test rather than depending solely upon the rapid slide agglutination test results.