A simple bactericidal antibody test for sero-diagnosis of typhoid fever

Serum samples were collected from 24 confirmed cases of typhoid fever, 15 clinically suspected cases and 23 normal healthy controls. The convalescent sera were obtained in 13 of the 24 confirmed typhoid cases. In all, 13 paired sera, 11 acute phase only, 15 clinically suspected and 23 normal serum samples were tested for eliciting bactericidal antibodies to Salmonella typhi. In addition, the Widal test was also performed for comparison. All the 24 acute phase sera as well as 13 convalescent sera were found to be positive by bactericidal antibody test (titre 1:80 or above). Of 15 clinically suspected cases, 5 were positive whereas one of the 23 normal controls sera gave a false positive reaction. In contrast, the Widal test could detect only one of the 24 cases in the acute stage, but all 13 cases showed antibodies at a diagnostic titre level during the convalescent stage. None of the 15 clinically suspected cases or 23 normal controls were positive by the Widal test. The feasibility of using a bactericidal antibody test in sero-diagnosis of typhoid fever is discussed.