An outbreak of mixed infection with EHEC O157:H7 and other diarrhegenic bacteria among high school students having traveled on a school excursion to China, October 1999 - Akita
(IASR 2000; 21: 94-95)

In April 1998, high school A students in Akita City had traveled on a school excursion to China, and they were infected with enterohemorrhagic Escherichia coli (EHEC) O26 and Salmonella Albany, etc. Details were reported to IASR Vol.19;No.10. During October 14 to 19, 1999 the high school A conducted an excursion to China. This time students were infected with EHEC O157:H7 and multiple bacterial pathogens.

Since October 18, a student presented signs of food poisoning, such as abdominal pain, diarrhea. On October 21, the patient's stool was forwarded to the Akita Prefectural Institute of Public Health, and the following day enterotoxigenic E. coli (ETEC) O167 (LT+) and enteroaggregative E. coli (EAggEC) OUT were isolated. Field investigation conducted by the Akita City Health Center revealed that 420 students and teachers 208 (199 students and 9 teachers) developed symptoms. The health center concluded these cases were due to food poisoning. On October 22, stool specimens of 206 cases were submitted to the Institute.

Because of previous year's experience, possibility of double infection was considered. EHEC screening was carried out by polymerase chain reaction (PCR) and isolation culture using CT-SMAC, CT-RMAC, DHL. Other possible bacteria were also considered for PCR screening and routine bacterial examinations.

EHEC O157:H7 (VT2+, eaeA+) are isolated from 6 cases. Twenty-seven EAggEC, 12 ETEC, 28 AEEC were isolated. These isolates had different serotypes and pathogenic genes. In addition, 4 types of Salmonella were isolated from 8 cases, and Campylobacter was isolated from a case. Secondary infection of EHEC O157:H7 to their families was not observed. Six isolates of EHEC O157:H7 had 2 patterns by pulsed-field gel electrophoresis (PFGE) using XbaI. Compared with patterns of EHEC O157:H7 isolated in Akita Prefecture recently, Chinese patterns had few more bands on 400kb area.

Regarding with EAggEC, ETEC, and AEEC examinations, PCR screening was initially conducted using EC broth of stool specimens. Stool specimens were inoculated on DHL for bacteria isolation. Because of large number of specimens, 5 colonies were selected from PCR-positive specimens. Of 138 PCR-positive specimens, bacteria were isolated from 67 (49%) specimens. Timing of onset and nil episode of secondary infection to the patients' families suggested that the patients were infected in China.

Reported by Jun Yatsuyanagi, Shioko Saito, Isao Ito, Hiroyasu Sato, and Yoshimichi Miyajima, Akita Prefectural Institute of Public Health

Correspondence: Jun Yatsuyanagi;
E-mail: jyatsu@spica.freemail.ne.jp

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