The validity of single-tube Widal test in diagnosis of typhoid fever

The Widal test is widely used for the serological diagnosis of typhoid fever in areas of endemicity, such as Iran, but the results of a single Widal test, are virtually un-interpretable unless the sensitivity and specificity of the test for the specific laboratory and patient population are known, so we have evaluated the validity of a single acute-phase Widal result for the diagnosis of typhoid fever in Iran and calculated the likelihood ratio at each titers of the Widal test. Methods and Material: The study was performed at the Bu-Ali Hospital in Zahedan, in the region of southeast Iran. Patients were grouped into two categories: 149 blood and or bone marrow culture-positive typhoid cases, and 226 nontyphoidal febrile cases. The results of two groups were analyzed by the test performance, namely, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), likelihood ratio for positive and negative results. Widal test was negative in 47% of typhoid patients and 83% of non-typhoid patients. The ratio for H agglutinin was 19 and 65%, respectively. Mean interval for patients was 13 and in non-typhoid patients it was 14.2 days. Sensitivity of O agglutinin was low even with titters of 1:80 (49%), but its specificity was high (90%). H agglutinin had a higher sensitivity and a lower specificity. Likelihood ratio of positive O agglutinin with different titters was relatively good. H agglutinin with titters higher than 1/80 had good likelihood ratio, but likelihood ratio for negative results of titters 1/40 and 1/80 of H agglutinin was desirable and it was not desirable for other titters. In hospital conditions, positive results of Widal test highly increase post-test probability, but negative results do not decrease the possibility of typhoid significantly.