Influence of Stx2 Subtype on Bacteriological Identification of Outbreaks of EHEC O157：H- Infections in Saitama City

Abstract

In 2013, two outbreaks of enterohemorrhagic Escherichia coli (EHEC) occurred in Saitama city. According to reports from each of the medical institutions that detected the EHEC isolates, the isolates seemed to differ in their production of Vero Toxin (VT / Shiga Toxin: Stx) since one isolate produced only Stx1 and the other produced both Stx1 and Stx2. However, a patient survey conducted by a public health center revealed that common foodstuffs had been consumed in both outbreaks. Because, the two EHEC isolates were newly detected from two people in one patient's family, we analyzed the phenotypic and genetic relationships among four isolates in total. All the isolates were serotyped as O157: H-, and both stx1 and stx2 were detected. Subsequently, all four isolates were shown to have the same pulsed-field gel electrophoresis (PFGE) banding pattern. The findings suggested that these isolates belonged to the same strain group. Among these cases, the isolates had stx2c which is one of the stx2 subtypes. Reportedly, some cases with the Stx2 subtype can not be detected using conventional tests for toxin. In addition, Stx2 can be overlooked as a result of this limitation of Stx-production tests. Both epidemiological research by public health centers and genetic analysis by prefectural and municipal public health institutes (PHIs) are very important for clarifying possible relationships among outbreaks, as in the present cases. Moreover, collaborations and networks among medical institutions, PHIs and public health centers should be further strengthened to prevent the spread of infections.