Epidemiological analysis of Shiga toxin-producing Escherichia coli O157 isolates from familial infection

Abstract

A total of 201 Shiga toxin-producing Escherichia coli (STEC) O157:H7 isolates from 22 epidemiologically unrelated familial infections in Osaka were analyzed by various epidemiological markers, such as Shiga toxin (STx) typing, antimicrobial resistant patterns, colicine typing, plasmid profiles and pulsed-field gel electrophoresis (PFGE) typing. There were two cases where different type strains were detected in a family (family No. 21 and 22). In the family No. 21, three different strains were isolated from a 5-year-old male infant; one identical with that from his mother, and the others different in 4 markers except STx type. In the family No. 22, two kinds of strain were detected in a 48-year-old father; one identical with those from other members of the family, and the other different in STx, plasmid profile and PFGE types. These facts showed the possibility of a simultaneous double infection from the common sources of infectious factors or a successive reinfection with different types of the agents. Identical marker strains were detected from 8 out of 12 familial infection cases from July to September. Although infectious sources of these cases are not yet clearly identified, these results of epidemiological markers analysis indicate a probable circulation of the common contaminated foodstuffs. A combined use of phenotypic and genotypic tests were shown to be useful for the epidemiological analysis. Further, it seemed necessary to examine epidemiological markers of more than one strain in familial infection or identical facilities generation cases. And also a collective analysis of the relating factors such as biological markers of the causative agents, the list of eaten foodstuffs, and successive outbreaks of the patients was thought most important.