Interpretation of the Widal Test in Infected Children

Abstract

Typhoid fever is endemic in Iran. Isolation of S. typhi is a gold standard for diagnosis. Laboratory diagnosis of S. typhi infection relies on serological tests such as the Widal test. This study describes seroprevalence of TO and TH antibody in nonfebrile healthy and febrile with non-typhoid illness. For detection of sensitivity and specificity of Widal test in typhoidal fever diagnosing Widal test was performed on serum specimen of the culture-positive cases of typhoid fever in children aged between 1 and14 years in Tehran, A cross –sectional study was carried out. Widal tests were performed on 40 healthy nonfebrile children; 40 patients with non typhoidal febrile illness and 58 cases with bacteriologically documented typhoid fever specificity, sensitivity, positive and negative predictive values and the efficacy of the test were determined. Agglutinin titres ≤ 1:40 were considered normal for TO and TH at 96.25% and 93.75% confidence levels, respectively. Titres above these levels. TO>1:40 and TH>1:40, were considered to be abnormal. 25% of patients showed no response to either agglutinin (TH and TO); and 44.8% of cases shown no response for TO agglutinin. TO >1/320 was not seen in any cases but TH >1/320 was detected in 20.6% of cases. Salmonella typhi TO and H agglutinin titers > 1/40 were considered to be significant with 75.86% sensitivity and 93.75% specificity, respectively. The positive and negative predictive values were 89.79% and 84.26%, respectively. This study suggests that seroprevalence studies in healthy children can help as validate use for particular serological cut-off point.