Widal agglutination titres in the diagnosis of typhoid fever.

BACKGROUND

Typhoid fever has continued to pose considerable health problems world-wide. This problem is made worse by misdiagnosis through the use of a single pretreatment Widal agglutination test in may developing countries.

OBJECTIVE

This is to enable us establish the appropriate titres suitable for a reliable diagnosis of typhoid fever in our environment.

METHODS

A total of 300 subjects were recruited into the study comprising 260 apparently healthy individuals aged 12 years and above and 40 patients with typhoid fever confirmed by isolation of S. typhi from blood and/or stool. The Widal slide agglutination test method was first used to screen subjects. Serum samples showing agglutination were then serially diluted with 0.85% saline from 1/40 to 1/1280 and subjected to tube dilution.

RESULTS

Thirty-six (13.8%) of the healthy subjects had S. typhi 'O' agglutinin and 48(18.5%) had 'H' agglutinin in their serum while 37(92.5%) of patients with culture-confirmed typhoid fever had 'O' agglutinin and 38(95.0%) had 'H' agglutinin. At a cut-off titre of 'O' agglutinin = 80, the diagnostic sensitivity and specificity were 90% and 87.3%, and for 'H' agglutinin = 80, the sensitivity and specificity are 90% and 88.5% respectively. The predictive value of a positive test at 'O' = 80 is 52.2% and of a negative test is 98.3% while the positive predictive value of 'H' = 80 is 54.6% and negative predictive value is 98.3%.

CONCLUSION

Because of the difficulties in isolating S. typhi from blood, stool or other body fluids in developing countries, a diagnostic Widal agglutination titre of 'O' and 'H' agglutinins = 80 will be considered useful in the diagnosis of typhoid fever in our environment.