Comparison of Widal Screening Test with Cultural Isolation Method for Diagnosis of Salmonella typhi/paratyphi Infections

Summary: The effectiveness of the Widal screening in comparison with stool and blood cultures for
typhoid/paratyphoid fever diagnosis in exposed subjects was evaluated. A total of 1000 (500 stool and
500 blood each) samples from 248 males and 252 female aged, < 1 -68 years was analysed. Widal
screening test was carried out on the blood using commercial antigen, following manufacturer’s
instructions. The isolation of organisms from blood and stool samples and identification were carried
out with standard methods. Characterization was done using polyvalent sera and confirmed using
single factor sera. The rates of recovery of S. paratyphi A, B, C and typhi D from stool and blood
cultures of positive subjects at the various Widal antibody titres were evaluated. Among the subjects
positive for S. paratyphi A at 1:160 Widal titre of O and H variants, the isolation rate from stool was
37.5%, while at 1:80 titre 39.1% was isolated from both blood and stool of each subject combined. For
those positive for S. paratyphi B at 1:160 positive titres, the isolation rates from stool and blood
sample cultures combined was 46.7%. The 1:320 positive titre for paratyphi C had peak isolation rates
(41.7%) from blood samples singly. In the case of S. typhi D the peak isolation rate (47.4%) was from
blood at titre of 1:320. There was significant difference (P= .001) among the rates of isolates of S.
typhi D from blood, stool and stool/blood cultures with thatusing Widal screening. However, there was
no correlation among the data (r= .256, .309 and .235 respectively). Blood culture is a major aid to
recovery and isolation of the organism in early stages of infection. Stool culture, though not very
specific, may also be used as diagnostic method. Widal test, though only a screening method is also
sensitive but only results yielding high titre are reliable.