Comparison of rapid tests (antigen vs. antibody) for the diagnosis of typhoid in the first and second weeks of fever

Abstract

Objectives: We conducted this study with an objective to compare the diagnostic accuracy of rapid antigen and antibody kits for early detection (<5 days of fever) and late detection (>5 days of fever) of S.Typhi and S.Paratyphi in relation to the Widal test. Methods: A cross-sectional observational study was conducted over 15 months, during which 180 cases of documented fever were enrolled. Paired samples (at <5 and >5 days of fever) were processed for rapid antigen test (RAg), rapid antibody test (RAb) and Widal test. Blood culture (BacT/Alert system) was considered as the gold standard for confirmation. Results: The mean (SD) age of patients with enteric fever was 16.42 (12.53) years, with a slight male preponderance (58.33% males vs. 41.67% females). Positive blood culture was reported in 58 (32.22%) cases. For RAg, RAb and Widal tests, the diagnostic accuracy was 45.56%, 42.22% and 41.11%, respectively, which was comparable for diagnosing enteric fever in cases with <5 days of fever ( P = 0.675). For fever >5 days, RAg showed a significantly lower diagnostic accuracy (15%) as compared to RAb (61.11%) and Widal test (66.11%) ( P < 0.0001). Conclusion: The study concludes that RAg marks a high sensitivity of accurate diagnosis in the initial five days of typhoid fever while RAb (with or without Widal tests), hold a superior sensitivity for diagnosis after five days of onset of enteric fever.