[Table of Contents]

Volume: 24S5 - September 1998

Canadian Integrated Surveillance Report for 1995 on Salmonella,
Campylobacter and Pathogenic Escherichia coli

Human Pathogenic E. coli Cases

Table of Contents

There were 1,455 human cases of pathogenic E. coli infection reported through provincial laboratories to the NLBEP database. This was higher than the number reported in 1994 (1,014) and 1993 (1,212). Summary data for 1,493 verotoxigenic E. coli cases were reported and verified as correct by provincial and territorial public health units to the NND database. Rates from the NLBEP and NNDS databases by province are presented in Figure 29. Individual case data were received from seven provinces and one territory, for 1,365 cases. The differences in number of cases between these databases likely reflect the different chains of reporting and within-province protocol for reporting. This is especially evident when laboratory and notifiable diseases rates within each province are compared. These rates are similar for seven provinces but differ by a factor of 2 to 7 for the other provinces. Different reporting paths among provinces will also affect the number and type of cases reported. Therefore, variation in reported rates among provinces, as presented in Figure 29, must be interpreted with caution.

Figure 29 Rates of human pathogenic E. coli cases (per 100,000 population) as reported through the National Notifiable Diseases system (upper numbers) and National Laboratory for Bacteriology and Enteric Pathogens (NLBEP) system (lower numbers) by province for 1995

Pathogenic E. coli Serovars

Most (91.3%) of the pathogenic E. coli isolates from human cases were serovar O157. The most frequently reported serovars are listed in Table 10. The number of cases reported increased from 1994 for the top four serovars.

Long-Term Trends

The total annual number of E. coli O157 cases reported in the NLBEP database increased to peak levels in the late 1980s and then gradually decreased (Figure 30). Verotoxigenic E. coli has been a notifiable disease since 1990 and shows a similar pattern to laboratory  E. coli O157 cases.

Figure 30
NLBEP and NNDS

1995 Trends The pathogenic E. coli cases showed a strong seasonal trend, with increased rates in the summertime and fall (Figure 33). The western provinces reported the highest incidence.

Unusual Infections

Pathogenic E. coli was isolated from blood in nine cases: O1 (2 cases), O2 (1 case), O4 (2 cases), O25 (1 case), O75 (1 case) and two cases in which the serovar was not specified.  Pathogenic E. coli was isolated from other, non-stool sources in five cases: O1 (1 case), O113 (1 case), O157 (1 case)  and two cases in which the serovar was not specified.

Hospitalizations and Deaths

From the NND Individual Case database, there were 156 (364.5/1,000 cases) inpatient and 13 (30.4/1000 cases) outpatient hospital visits associated with pathogenic E. coli cases in 1995. Four deaths (39.2/1,000 cases) were reported to be associated with pathogenic E. coli cases. Less than 32% of cases came with information on hospitalization and outcome, and only those cases for which information was provided were used to calculate these rates. Therefore the rates may be biased.

Outbreaks

There were 30 pathogenic E. coli cases associated with 16 outbreaks recorded in the NLBEP database for 1995, and all those that were specified were serovar O157. This is similar to the number of cases (46) reported from outbreaks in 1994. Most of the outbreaks were reported to be family  associated.

In the 1995 NND database, 41 cases were associated with outbreaks, and these were reported from only Ontario (35) and British Columbia (6). There is no indicator to link cases with specific outbreaks, but using date and the first three digits of the postal code, the cases could be grouped into apparent outbreaks. Thus, nine outbreaks were reported, seven from Ontario and two from British Columbia. None of these nine outbreaks matched the two outbreaks identified in the NLBEP database for these provinces. This illustrates the under-reporting of outbreaks in these databases.

A risk factor was specified for 8% (104) of the pathogenic E. coli cases in the NND database. Of these, 54% (56) had reported home, 29% (30) had reported restaurant, 13% (14) had reported travel and 4% (4) had reported day care as a risk factor for the case.

Age Distribution

The age distribution of cases reported to the NND Individual Cases database for each of these three pathogens showed a peak in children < 2 years of age, which extended to about 10 years of age (Figure 36). Campylobacter and Salmonella cases showed smaller secondary peaks in the 20-35-year-old age range, but no such peak was observed for E. coli cases.

Data from Notifiable Diseases Summary database

The lower number of verotoxigenic E. coli and Campylobacter cases in the < 1-year-old children compared with 1-year olds is at least partially due to the fact that babies born in 1995 were at risk for only half the year, on average. This suggests that risk of salmonellosis is much higher for children < 1-year old than for 1-year olds.

The proportion of cases < 1 year of age was higher for Salmonella (8%) than for E. coli (4%) and Campylobacter (2%). However, the proportion of cases < 10 years of age was higher for E. coli (40%) than for Salmonella (32%) and Campylobacter (20%).

[Previous] [Table of Contents] [Next]