Phage typing and DNA-based comparison of strains of enterohemorrhagic Escherichia coli O157 from apparently sporadic infections in Osaka City, Japan, 1996.

A marked increase in sporadic cases of enteritis due to enterohemorrhagic Escherichia coli serogroup O157 occurred in Osaka City, Japan, during 1996. To elucidate why the number of cases had increased, the isolates were classified using phage typing, random amplified polymorphic DNA analysis, and pulsed-field gel electrophoresis (PFGE). Fifty-seven percent of the isolates (105/184) belonged to the same phage type (PT-32) and gave the same PFGE pattern; the clone had been isolated during a 3-week period, with a peak on July 15. It was concluded that the majority of the cases identified in July 1996 formed an outbreak, although epidemiological links to a possible common source were not established. The possibility that this outbreak was part of a huge regional outbreak including children at primary schools in Sakai City was discussed.