Evaluation of a latex agglutination test for salmonella and shigella in stool specimens

ABSTRACT

We evaluated the Bactigen Salmonella- Shigella Latex Agglutination Test [BSST] for the detection of Salmonella and Shigella antigens in Gram negative broth inoculated with stool and rectal swab specimens and incubated for 12-24 hours. Of the 474 specimens tested, five were not interpretable due to nonspecific agglutination [NSA]. Of eleven specimens which were culture positive for Salmonella, nine were also positive by BSST [sensitivity 81.8 percent]; however, seven specimens were falsely positive for Salmonella [specificity 98.5 percent and positive predictive value 56.2 percent]. None of the three Shigella positive cultures was detected by BSST, although one was not interpretable due to NSA. No false positive results were disclosed for Shigella either [Sensitivity 0 percent, specificity 100 percent]. We conclude that although BSST may be useful as an additional procedure for the early detection of some cases of Salmonella infections, it is not sufficiently reliable to replace conventional methods of stool culture due to its low sensitivity. BSST does not appear to be useful for the detection of Shigella