Since 1993 till 2011, the surveillance system for Laboratory Findings of Infectious Agents in Japan (IASR 31: 75-76, 2010) classified diarrheagenic E. coli into five categories, i.e., EHEC/VTEC, ETEC, EIEC, EPEC and “other diarrheagenic E. coli ” (Table 1a). The food poisoning statistics, however, classified the diarrheagenic E. coli into two categories of EHEC and “other pathogenic E. coli ” since 1998. This article deals with diarrheagenic E. coli other than EHEC.
Report of pathogen detection: Fig. 1 shows the summary of all the data sent in two formats (“Outbreak pathogen report” and “Monthly isolation of pathogenic bacteria from humans”) from prefectural and municipal public health institutes (PHIs) and health centers on outbreaks and detection of diarrheagenic E. coli other than EHEC/VTEC, i.e., ETEC, EIEC, EPEC and “other diarrheagenic E. coli ”. Both incidents and patients increased in number in summer seasons, but not a few cases occurred in winter. Incidents due to ETEC were at the top in both outbreak numbers and patient numbers. ETEC cases tended to decrease until 2009, but are on rise from 2010 to 2011. Reports of EIEC are only a few.
The third format “Individual case report on pathogen isolation/detection” includes information for O-group serotyping, although only a part of detected case is reported in particular for ETEC. According to this information, from January 2001 to August 2011, 374 ETEC, 9 EIEC, 590 EPEC and 92 “other diarrheagenic E. coli ” cases were reported (see p. 3 of this issue). Until now, EPEC was determined by O group (Table 1a). One-third of the reported EPEC were O1 and O18. Only three strains of the reported O1 and O18 were positive for eae , an important marker of EPEC. Inversely, when the eae -positive EPEC isolates were classified for the O group, the most frequent were OUT, O55, O128, O119 and O8. Among strains positive for aggR , OUT, O126, O127, O111 and O78 were frequent.
Outbreaks: From 2008 to 2010 (from Statistics of Food Poisoning in Japan, 2008-2010, Ministry of Health, Labour and Welfare), there have been annually 8-12 outbreaks due to “other pathogenic E. coli (other than EHEC)” and 160-1,048 patients involved (Table 2 in p. 3 of this issue). The patient number decreased after the peak in the year 1998 (IASR 29: 213-215, 2008 & 31: 1-3, 2010), but increased in 2010 due to outbreaks described below.
As for large-scale outbreaks involving more than 500 patients per incident, there were five such incidents from 1997 to 2000, but from 2000 to 2009 they were absent. A big outbreak occurred again in 2010 (Table 3) and the patient number jumped up. Another outbreak occurred in 2011, which was caused by ETEC O148:H28 that contaminated foodstuffs provided to many cafeterias in wide area by one company (see pp. 9 & 12 of this issue). The causative agent was detected from the leftover of the food material green onions.
Outbreaks, not necessarily large scale ones, are often caused by ETEC (Fig. 1), and less frequently by EAggEC (see p. 7 of this issue and IASR 29: 226-227, 2008) and EPEC (see p. 8 of this issue and IASR 32: 143-144, 2011).
Laboratory detection (see p. 4 of this issue): It is difficult to classify diarrheagenic E. coli by clinical symptoms, biochemical characteristics of isolates or by O-group serotyping. Differentiation by pathogenic factor detection is critically important. Pathogenic factors include toxin-production (EHEC/VTEC and ETEC), cell invasiveness (EIEC), and cell adhesiveness (EPEC and EAggEC). They can be diagnosed by biological and immunological methods, but more recently PHIs use PCR for detecting bacterial genes encoding the pathogenic factors (see pp. 7 & 8 of this issue).
Reclassification of diarrheagenic E. coli needed (see p. 5 of this issue): Under the pathogen detection reporting system till 2011, EPEC had been classified by O-group serotyping, which was increasingly found problematic. For example, some EAggEC strains were classified as EPEC. Inversely, some eae -positive strains not belonging to known EPEC O groups had been discarded as non-EPEC. Non-pathogenic O1 and O18 strains frequently isolated from healthy persons were reported as EPEC.
In order to solve the above problems, PHIs and National Institute of Infectious Diseases examined the issue and concluded to use intimin gene (eae ) in place of O-group serotyping as a primary pathogen marker of EPEC strains from 2012 (Table 1b). In addition, EAggEC was added to the list of diarrheagenic E. coli using aggR gene as a marker. These arrangements will bring Japanese system consistent with the globally used classification of diarrheagenic E. coli (Manual of Clinical Microbiology, 10th Ed, Chapter 35).
Concluding remarks: In 2011, in Germany and in other EU countries, a new type diarrheagenic E. coli , O104:H4, emerged, which had insertions of verotoxin gene and others in EAggEC (aggR gene) type strain. The diarrheagenic E. coli may further acquire additional multiple pathogenic factors in future, which should be closely monitored.
As EAggEC and EPEC have not been well investigated for their pathogenicity, such isolates are very often discarded from reports particularly when they are isolated from sporadic cases. It has been reported that an outbreak of foodborne illness, from which EAggEC was isolated, was handled as a “consumer complaints” event, not as “food poisoning” (see p. 7 of this issue).
PHIs are requested to report all the detected diarrheagenic E. coli cases according to the newly revised standard of pathogen reporting, which is based on the detection of the pathogenic factors. Analysis of the collected data including investigation of pathogenic factors detected from outbreak cases is crucial for correct understanding of the diarrheagenic E. coli epidemic in Japan. The questionnaire-based survey done by PHIs indicated the necessity of laboratory investigation manual on diarrheagenic E. coli (see p. 4 of this issue), which should be drafted as soon as possible.