Evaluation of two rapid methods to screen pathogens from stool specimens

Two rapid methods, the Enteric Pathogen Screen (EPS) cards of the AutoMicrobic system (Vitek Systems, Inc., Hazelwood, MO) and the Bactigen Salmonella-Shigella latex agglutination (LPA) method (Wampole Laboratories, Cranbury, NJ) were compared with conventional biochemical tests to screen stool cultures having suspicious colonial morphologic characteristics for the presence of Salmonella and Shigella in a study of 481 isolates from stool specimens and 104 stock cultures. Compared with conventional testing, overall, 327 of 394 (83%) clinically irrelevant organisms resulted in a report of no Salmonella spp., Shigella spp., or Yersinia enterocolitica with EPS. Four hundred forty-nine of 457 (98%) of clinically irrelevant organisms yielded negative LPA results. Because the LPA method is faster, eliminates more clinically irrelevant organisms from further testing, and does not require the use of an expensive identification system, the authors believe that it is better suited for direct screening for Salmonella and Shigella for most clinical laboratories.