Abstract
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.
Highlights
Enteric fever is an important cause of morbidity in many regions of the world, with an estimated 13 million cases occurring annually in Asia alone.[1]
Laboratory diagnosis mainly depends upon isolation of causative agents from specimens like blood and bone marrow
All the blood samples requisitioned and received in the microbiology laboratory for Widal test from patients suspected as having enteric fever during the study period were included in the study
Summary
Enteric fever is an important cause of morbidity in many regions of the world, with an estimated 13 million cases occurring annually in Asia alone.[1] Estimates suggest an incidence rate of more than 21.5 million cases globally in the year 2000.[2]. In India, enteric fever is caused by Salmonella enterica serotype Typhi and Paratyphi A. Laboratory diagnosis mainly depends upon isolation of causative agents from specimens like blood and bone marrow. A blood culture gives positive results in 73-97% cases before the use of antibiotics.[3] the availability of microbiological culturing facilities is often limited in many typhoid endemic regions and blood cultures can be negative when patients have received prior antibiotic therapy.[1] serological diagnosis using Widal test is relied upon in many cases
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