Fluorescent Vi antibody test in the screening of typhoid carriers.

The comparative efficacies of direct bacterial agglutination and immunofluorescent antibody for the estimation of serum Vi antibody were determined in the detection of typhoid carriers. Sera from all 12 typhoid carriers gave significant titers of 1/10 or more in the direct bacterial agglutination test; however, 26 of 119 (21.8%) sera from culture-negative individuals were also falsely positive. In the fluorescent Vi antibody test, 11 of 12 typhoid carriers showed significant serum antibody levels, while only two of 119 (1.7%) culture-negative subjects had significant antibody titers. In view of the much lower false-positive rate, the immunofluorescent Vi antibody test is considered to be superior to the direct bacterial agglutination test in the screening of typhoid carriers.