Evaluation of passive bacterial agglutination for the diagnosis of typhoid fever

We evaluated the reliability of a passive bacterial agglutination test to detect Salmonella typhi somatic antigen(s) in the sera of patients with typhoid fever. It was positive in 32 of 33 bacteriologically proven typhoid fever cases. Among 13 patients with a presumptive diagnosis of typhoid fever, 11 were positive by passive bacterial agglutination. The serum of one patient with paratyphoid A was also positive. Among 50 febrile patients without typhoid fever, one was persistently positive during the course of illness; 49 were negative. The sensitivity, specificity, and accuracy indices of the passive bacterial agglutination test were over 95%. The positive and negative predictive values were 94 and 98%, respectively.