EVALUATION OF THE MOLECULAR EPIDEMIOLOGY OF AN OUTBREAK OF MULTIPLY RESISTANT SHIGELLA-SONNEI IN A DAY-CARE-CENTER BY USING PULSED-FIELD GEL-ELECTROPHORESIS AND PLASMID DNA ANALYSIS

Outbreaks of diarrhea in child day-care centers (DCC) are common. This study was undertaken to evaluate the molecular epidemiology of an out break of diarrhea due to Shigella sonnei. This outbreak involved 25 of 52 (48%) DCC children and 14 of 132 (11%) teachers and household cont acts. S. sonnei isolates from nine children and five contacts were cha racterized by antimicrobial susceptibility, plasmid content, plasmid D NA restriction fragment pattern, and pulsed-field gel electrophoresis (PFGE) of total genomic DNA; 33 isolates from Houston, Tex., Chicago, Ill., and Mexico City, Mexico, also were studied. All outbreak isolate s were resistant to ampicillin and trimethoprim-sulfamethoxazole and s hared five to six plasmids ranging from 3.3 to 70 MDa. A total of 8 of 12 temporally associated nonoutbreak Houston isolates had plasmid pro files and restriction fragment patterns similar to those of the outbre ak strain, despite possessing different antibiotic susceptibility patt erns. PFGE demonstrated identical DNA patterns among outbreak isolates and similar or identical patterns among temporally associated sporadi c Houston isolates with plasmid profiles similar to that of the outbre ak strain. All other nonoutbreak strains from Houston, Chicago, and Me xico had plasmid profiles, restriction fragment patterns, and PFGE pat terns different from those of the outbreak strain. DCC outbreak isolat es could be distinguished from most sporadic isolates by antimicrobial susceptibility testing, but plasmid analysis and PFGE could not diffe rentiate common-source isolates from sporadic isolates in the same loc ation during the same time period, indicating that isolates present in the community were genetically similar to those producing outbreaks i n the DCC.