Phylogenic analysis (clade analysis) of causative strains in the first outbreak of enterohemorrhagic Escherichia coli O157:H7 in Yamaguchi Prefecture and the actual state of infection by clade 8 of the highly virulent O157:H7 clade in Yamaguchi Prefecture
2014
Tominaga, K. (Yamaguchi Prefectural Institute of Public Health and Environment, Yamaguchi-city, Yamaguchi-ken (Japan)) | Yabata, J. | Kameyama, M. | Iyoda, S.
In November 1998, the first outbreak of enterohemorrhagic Escherichia coli O157:H7 (O157) Stx2 infection occurred in a special nursing home for the aged in Yamaguchi Prefecture. Thirty-two patients developed symptoms, and three died. Severe disease in the form of hemolytic uremic syndrome (HUS) was observed in eight patients, including the three who died, and the aggravation rate (ratio of number of patients with HUS to the number of symptomatic patients) was extremely high. Therefore, we analyzed 166 O157 isolates in Yamaguchi Prefecture, including the outbreak strains, by the phylogenetic analysis (clade analysis) method developed in the United States and investigated how often the presumably highly virulent clade 8 strain was isolated. Of the 166 strains, 21 (21.7%) were identified as clade 8 strains. All strains from the 1998 outbreak were identified as clade 8 strains; thus, one of the factors associated with the high aggravation rate in this outbreak might have been the highly virulent phylogenetic lineage. Additionally, among the isolates from 2004 to 2011, one to five strains were identified as clade 8 strains every year except 2008. Therefore, sporadic infections of clade 8 strains occurred almost every year in Yamaguchi Prefecture. In 2011, a small outbreak occurred in which clade 8 strains were isolated in four successive cases within a short period of time. Genotyping by the IS-printing method revealed that the clade 8 strains were characterized by unique IS profiles never previously recognized in other clades.
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