The Topic of This Month Vol.17 No.1 (No.191)
Verotoxin-producing Escherichia coli (VTEC) is an agent of hemorrhagic colitis with such main symptoms as severe abdominal pain and hemorrhagic diarrhea, being often complicated with hemolytic uremic syndrome (HUS). In Japan, information on VTEC isolation has been collected since 1991 with Verotoxin-producivility or Verotoxin (VT)-coding gene as a parameter. This report is a summary of incidence of VTEC infection reported to the Infectious Agents Surveillance Center from January 1991 through December 1995.
During the five years from January 1991 through December 1995, reports of VTEC isolation by prefectural and municipal public health institutes in the whole country numbered 351, which accounted for 5.2% of 6,783, the number of all the reports on isolation of enteropathogenic E. coli during the same period. The reports on VTEC isolation sent in by general clinical institutions during the same period numbered 114 (Table 1).
The status of monthly isolation of VTEC shows a pattern of high incidence in summer of diarrheal disease due to this organism with a peak in July-August. The high incidence in July 1993 and October 1994 reflects the outbreaks in Tokyo and Nara, respectively (Fig. 1).
The status of VTEC isolation by serotype and VT type is shown in Table 2. VTEC isolated during January 1991-November 1995 included 10 different O serotypes. The most frequently isolated was O157:H7, which accounted for 82% (379 instances). Of 430 VTEC strains isolated during 1991-1994, 316 (73%) were VT1 and VT2 producers, 72 (17%) VT2 producers, and 21 (4.9%) VT1 producers. All 11 strains of VTEC serotype O26 including four isolates in 1995 were those producing VT1 alone.
The age distribution and clinical symptoms of the 430 cases yielding VTEC reported during 1991-1994 are shown in Table 3. The age distribution shows a tendency of high incidence among young generations; 40 (9.3%) were under one year, 96 (22%) 2-5 years, and 223 (52%) 6-15 years. The youngest case was 5 months old and the eldest one 85 years old. The sex ratio of the 430 cases was 1.02; there were slightly more male cases than female cases.
HUS was seen in 29 cases (6.7%), of which 15 (52%) were under 5 years old. Besides, nine cases of 6-15 years old and four cases of greater equal 16 years old were reported. Three HUS cases including a fatal one (see p. 4 of this issue) have been reported in 1995. No other fatal case than this one has been reported since the collection of information started in 1991. The VTEC strains isolated from HUS cases were all of serotype O157. Cases from which VTEC O157 was isolated had hemorrhagic diarrhea in 32%, diarrhea in 32%, abdominal pain in 35% and fever in 13%. The corresponding ratios of the cases from which VTEC of other than serotype O157 were isolated were 16, 70, 61, and 6.8%, respectively.
The methods used for detection and typing of VT during 1991-1994 are shown in Table 4. Polymerase chain reaction (PCR) and reversed passive latex agglutination (RPLA) are often being used at present in this country; in 85% and 90% of instances of detection, respectively, in 1994. RPLA has rapidly become popular after commercial kits became available, whereas enzyme-linked immunosorbent assay has not been used since 1993 because of its somewhat complicated procedures. For detection of VT in 325 of 430 strains (76%), multiple methods were used; PCR and RPLA on 123 strains (29%), and PCR, RPLA and cytopathic effect on Vero cells on 93 strains (22%).
Outbreaks due to VTEC reported counted 12 in 1991 (see IASR Vol. 13, No. 7) and five in 1992 (see IASR Vol. 14, No. 10). Of these 17 outbreaks, 11 (65%) were familial ones, other four (24%) in nursery schools, and other two (12%) in primary schools. From 1993 through December 1995, 12 outbreaks have been reported (Table 5); eight were familial ones, and two each were those in nursery schools and primary schools. All of these outbreaks were due to VTEC O157:H7. The outbreaks of diarrheal disease during June-July 1993 in Tokyo (No. 2) and in October 1994 in Nara (No. 10) occurred in primary schools and cases of secondary infection were also reported. Of outbreaks of VTEC infection, familial ones are more common than school and other institutional ones in this country. Man-to-man transmission was strongly suggested by the epidemiology of the familial outbreak having occurred in October 1995 in Nara (No.12, see p. 3 of this issue). In most VTEC infections in this country, whether sporadic or in an outbreak, the source of infection was not specified. In outbreaks of VTEC infection, taking countermeasures not only as food poisoning but also as communicable disease are strongly desired.