Clinical Significance of Single Widal Test

Abstract

Introduction: To evaluate the usefulness of Widal test requested only once during the clinical episode(single Widal test) in diagnosing typhoid fever, results of culture for Salmonella typhi were compared to the results of single Widal test. Materials and Methods: Widal tests were performed by rapid slide melhod(stained Salmonella suspensions, Murex, England) and the cutoff values of Widal test liter were ≤ 1:160 for 0 antigen, ≤ 1:320 for H antigen. After reviewing culture results of S.typhi the sensitivity, specificity and efficiency of the single Widal test were computed. Results: Culture results of S.typhi in positive Widal test were 7.1%(9/126) for 0 antigen, 7.6% (11/134) for H antigen, 10.9%(6/55) for 0 & H, therefore false positive results were 92.9% for 0, 92.4% for H, 89.1% for 0 & H combined and false negative results were 0.7%(7/1022) for 0, 0.5% (5/1003) for H, 0.2%(2/1093) for 0 & H. The sensitivity, specificity and efficiency of single Widal test were 56.3% (9/16), 89.7%(1015/1132) and 89.3%(1026/1148) for 0; 68.8%(l 1/16), 88.2% (998/1132) and 87.8%(1009/1148) for H; 37.5%(6/16), 95.7%(1083/1132) and 94.9%(1089/1148) for O & H, respectively. Also, Widal test results were positive on many occasions when group D Salmonella was isolated even if isolates were not S.typhi and some group B Salmonella isolates, Conclusion: The outcome of single Widal test showed more than a 90% false positive rate for both 0 and H antigens. Furthermore, Widal tests were positive when patients were infected with Salmonella groups other than S.typhi. Therefore, it is concluded that single Widal test is not a good diagnostic test for typhoid fever.