Utility of A Single Widal Test in The Diagnosis of Typhoid Fever
Background & objectives: The clinical diagnosis of typhoid fever is difficult, as the presenting symptoms are often diverse and similar to those observed with other febrile illnesses. The definitive diagnosis of typhoid fever requires the isolation of Salmonella typhi or paratyphi from the patient concerned. Since patients often receive antibiotics prior to a confirmatory diagnosis, there is uncertainty that bacteria can be isolated from the blood cultures. Besides this, the facilities for blood culture are not always available or feasible. All these limitations have made Widal test the most utilized diagnostic test for typhoid fever. Many studies have produced data which had cast serious doubts on the value of the Widal Test and thus reappraisal of the role of a single Widal test is needed.
Methods & materials: This study was carried out to determine the changes in clinical pattern of enteric fever. A total of 153 children, aged 0 to 14 years, diagnosed as typhoid fever (either positive blood culture for Salmonella typhi or paratyphi) were induced in the study. Of them, 86 children were with a definitive diagnosis of typhoid or paratyphoid fever as indicated by the isolation of S. typhi or S. paratyphi from the blood and 17 had negative blood culture but were clinically suspected of having typhoid fever. The control group was comprised of 50 children with non-typhoidal fevers The Widal test was carried out using rapid slide agglutination method and its accuracy was assessed by comparing the findings with that obtained through blood culture.
Result: The mean age of the patients was 5.2 ± 2.8 years and the youngest and oldest patients were 0.7 and 14 years respectively and male to female ratio was roughly 1:1. Nearly one-quarter (24.6%) of the patients had been suffering from the disease for >10 days and the mean duration of illness was 8.2 ± 3.3 days. Widal Test result showed that an O agglutinin titer of cut-off value e1:40 gave a sensitivity of 87.2%, a specificity of 47.1%, a positive predictive value (PPV) of 89.2% and a negative predictive value (NPV) of 42.1%. The sensitivity and NPV decreased with the increase in titer levels and were 56.9% and 31.5% at cut-off value of e 1:320, while the specificity and PPV increased with the increase in titer levels from 47.1% and 89.2% respectively at a titer of e1:40 to 100% at a titer of e 1:320. The titer behaved in the same way as did the O agglutinin titer. Similarly when H agglutinin was used the sensitivity and NPV decreased from 65% and 31.7% at a titer of e1:40 to only 25% and 20% respectively at a titer of > 1:320, while specificity and PPV increased from 76.4% and 81.1% at >1:40 to 94.1% and 95.6% respectively at e 1:320. When either O or H antibody titer of e1:160 was used, a good sensitivity (71%), specificity (70.6%) and PPV (92.4%) resulted, though NPV decreased to 32.4%.
Conclusion: The Widal test can be of diagnostic value when blood cultures are not available nor practically feasible.
Bangladesh J Child Health 2011; Vol 35 (2): 53-58