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Retrospective review of dot enzyme immunoassay test for typhoid fever in an endemic area.

Typhoid fever remains a common problem in Malaysia, but for its diagnosis both blood culture and the Widal test have drawbacks. A dot enzyme immunoassay (EIA) has been developed which detects IgM and IgG antibodies to a specific 50 kDa outer membrane protein on Salmonella typhi. This study was performed among outpatients attending the university hospital in Kelantan, a state on the east coast of Peninsular Malaysia where typhoid is endemic. The dot EIA was done on 149 outpatients of all ages in whom typhoid was suspected. Of these, 60 were not analysable due to insufficient data. The other 89 were retrospectively classed as typhoid (total = 21), or not typhoid (total = 68). The criteria for diagnosis of typhoid was either, blood culture was positive, or with blood culture negative, temperature was at least 38 degrees C and Widal O and/or H titer greater than or equal to 1/160. We then compared the diagnosis with the EIA result. For the result where either IgM or IgG was positive, sensitivity was 90%, specificity 91% and negative predictive value 97%. For IgM positive, specificity was 100%. But the specificity of IgG positive alone was reduced by six false positives, which were probably due to persistence of IgG after acute infection. Other cases were found where IgG positive alone appeared in the first week of typhoid fever, probably due to rapid response in a second or subsequent infection. We also found that IgM-producing patients were significantly younger than those showing IgG alone positive.