Acute diarrhea outbreak caused by Shigella flexneri at a school in Madrid, Cundinamarca: phenotypic and genotypic characterization of the isolates.

Abstract

Shigellosis is an acute diarrhoeal disease that is the main cause of morbidity and mortality in developing countries. In 1997, the Colombian Instituto Nacional de Salud Microbiology Group organized a network surveillance program with the country's Public Health Laboratories (PHLs) to monitor the principal etiological agents responsible for acute diarrhoeal disease. In May, 2001, the PHL of the state of Cundinamarca reported a food poisoning outbreak involving an elementary school community. The main goal of the Microbiology Group involvement was to establish the molecular relationships among the isolates from the outbreak by phenotypic and genotypic methods of characterization. Stool cultures were obtained from 22 of 195 affected individuals. The Microbiology Group confirmed the identification of the isolates by biochemical and serological probes. The antimicrobial susceptibilities were tested against the following battery of antibiotics: chloramphenicol, trimehoprim-sulfamethozazole, cefotaxime, gentamicin, ampicillin and ciprofloxacin. The isolates were subjected to pulsed field gel electrophoresis (PFGE) using the following CDC (U.S. Centers for Disease Control) protocols: Xbal restriction enzyme, Shigella sonnei CDC F2353 as the reference standard, and lambda phage as a molecular weight marker. In 15 of 22 (68%) stool cultures Shigella was recovered, all isolates were identified as Shigella flexneri serotype 6 biotype Newcastle with the same antimicrobial susceptibility profile. PFGE showed that 3 (20%) isolates were identical (100% genetic similarity) and the other 12 (80%) were very closely related (genetic similarity between 86-98%). The network system permitted the INS ready access to the isolates and the implementation of the PFGE permitted a quantitative characterization of the clonal relationship among the isolates from the outbreak.