Molecular analysis of enterohemorrhagic Escherichia coli isolates in Japan and its application to epidemiological investigation

Many outbreaks of enterohemorrhagic Escherichia coli (EHEC) O157 infections occurred in Japan in 1996. Molecular epidemiological analyses of the isolates by methods such as XbaI-digested, pulsed-field gel electrophoresis (PFGE), revealed that a variety of PFGE type strains have spread all over Japan. They also showed that such molecular methods are very useful for confirming the epidemiologically related isolates and in assisting the epidemiological investigation. Recent characteristic features of the infection are that the incidence of patients experiencing symptoms such as abdominal cramps, diarrhea and hemorrhagic colitis is higher in children younger than 9 years old; however, that of asymptomatic carriers seems to be higher in adults; and that EHEC O157:H7-serotyped strains are still the main isolates, while the isolation frequency of other serotype strains, such as O26 and O111, is increasing.