Utilization of a Latex Agglutination Test for the Rapid Detection of Shigella in Stool Specimens of Children with the hemolytic Uremic Syndrome

Background: The hemolytic uremic syndrome (HUS) is one of the important causes of acute renal failure in childhood. It is classified into diarrhea-associated and atypical cases. Verotoxin-associated HUS is the most common type of the disease. It is characterized by the sudden onset of hemolytic anemia with fragmented erythrocytes, thrombocytopenia, and acute renal failure after a prodromal illness of acute gastroenteritis usually with bloody diarrhea. In addition to specific strains of E. Coli, Shigella dysentriae type 1 can be an important cause of HUS. Cases with Shigella dysentriae have ahigher mortality rate, and a greater incidence of complications and extra-renal manifestations compared with patients who have HUS related to E. Coli. Therefore, it would be important to have a rapid way to detect Shigella associated HUS, in order to anticipate its complications, and allow the administration of aggressive managements to such patients. Conventional stool cultures are labour-demanding and time-consuming, and therefore may not be the ideal method for the detection of certain stool pathogens in acute situation like the hemolytic uremic syndrome. A rapid, cost-effective and reliable method for the detection and identification of stool pathogens in stool specimens from these patients would be of great value.
Objectives: The aim of this work is to evaluate the utilization of a rapid latex agglutination test in comparison to conventional stool culture to determine the incidence of Shigella dysentriae among children with the HUS in Egyptian children, and to determine whether this test could be used as an alternative to conventional stool culture in this situation.
Methods: In this study, a latex agglutination test (Bactigen Salmonella/Shigellalatex agglutination slide test; Wampole Laboratories, Cranbury, NJ) was evaluated as a test for the detection of Shigella antigens in Gram Negative Broth for the early and rapid detection of Shigella dysentriae infection in infants and children presenting with evidence of the hemolytic uremic syndrome.
Results: Utilization of conventional stool culture revealed that 3 of 7 cases of the HUS were positive for Shigella dysentriae, an incidenceof 17%. Utilization of the BSST latex agglutination test for Shigella antigen shows that 5 of 17 cases of the HUS were positive for Shigella dysentriae (29.5%). Also, all 3 cases in which stool culture was positive for Shigella dysentriae were also positive by the BSST test, with no false negatives (sensitivity 100%, positive predictive value 80%). However, of the 14 cases of HUS who were negative for Shigella by culture, two cases were positive for Shigella by the BSST latex agglutination test (specificity 85%, negative predictive value 100%).
Conclusions: The BSST latex agglutination test is a useful method for the rapid detection of Shigella antigens in stool specimens from infants and children with the HUS. Due to its rapidity, it can provide a quick answer and allow the anticipation if the need for more aggressive managements for cases of HUS associated with Shigella gastroenteritis. Its sensitivity appears to be excellent. While its specificity appears to be low, with a high incidence of false positive results. However, in such an acute situation, it is much more important not to miss a positive case than to over-diagnosis a case with Shigellosis. Also, conventional stool culture can correctly identify the true pathogen in false positive cases.