Evaluation of a latex agglutination test for the detection of Salmonella and Shigella spp. by using broth enrichment.

We evaluated the Bactigen Salmonella-Shigella Latex Agglutination Slide Test (Wampole Laboratories, Div. Carter-Wallace, Inc., Cranbury, N.J.) for detection of Salmonella and Shigella spp. in enrichment broth cultures (gram-negative broth incubated for 24 h) as part of the routine testing of stool samples. A total of 1,128 stool samples were screened by using this test. Of 29 samples culture positive for Salmonella spp., 25 were positive with the Salmonella test (sensitivity, 86.2%; specificity, 96.2%). Of four stool samples culture positive for Shigella spp., two were detected with the Shigella latex reagent. Overall, the Shigella test had a specificity of 99.2%. Testing of enrichment broth cultures after 24 h of incubation was more sensitive than was testing after 6 h of incubation. When used for direct culture identification, both reagents had a specificity of greater than 98.0%. We conclude that the Salmonella test may be useful as an enrichment broth screening test to detect Salmonella spp.; however, we cannot make any conclusions about the Shigella test because of the low number of culture-positive specimens in this study.