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

Background: 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.
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 nontyphoid
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.
Conclusions: In hospital conditions, positive results of Widal test highly increase post-test
probability, but negative results do not decrease the possibility of typhoid significantly.