Infection caused by Escherichia coli O157:H7 in Alberta, Canada, and in Scotland: a five-year review, 1987-1991

Infections and life-threatening complications due to verotoxin-producing Escherichia coli (VTEC) have been increasingly recognized as a public health problem in recent years. Through enhanced surveillance in Alberta, Canada, and in Scotland, 1,993 cases of VTEC infection and 115 cases of hemolytic-uremic syndrome (HUS) were detected in 1987-1991 in a combined population of more than 7.5 million; there were 24 deaths. The mean annual rates of VTEC infection were 12.1/100,000 and 2.0/100,000 for Alberta and Scotland, respectively. One case of HUS occurred for every 14 (Scotland) to 19 (Alberta) cases of VTEC infection. Rates of VTEC infection were highest among children < 5 years of age, while rates of resultant hospitalization were highest among the elderly. Male-to-female ratios for patients with VTEC infection varied with the age group. The incidence of this infection was highest in the summer: 64.0%-81.7% of cases occurred between May and September. Hamburger was the most common source reported. Unexplained geographic variation in prevalence was evident in both Alberta and Scotland. Most cases were sporadic, although several community and point-source outbreaks were identified in Scotland. HUS exhibited similar epidemiological patterns. Infections with VTEC impose a substantial preventable clinical and public health burden. Routine monitoring of these infections is considered worthwhile in order to elucidate their epidemiology and modes of transmission and ultimately to control them more effectively.