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

Abstract

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. 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. 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 (<i>P</i> = 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%) (<i>P</i> < 0.0001). 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.