No Surprises in E. coli Outbreaks of Eastern and Central Canada: The Usual Food-Source, and PHAC’s Anticipated Race against Time!


The Public Health Agency of Canada (PHAC) , the institute in charge of responding to public health emergencies and infectious disease outbreaks, published a final update on the E. coli outbreak that occurred between July 6 and September 4, 2015, in Alberta, Ontario, Quebec and Nova Scotia. Of the 29 cases reported, seven were hospitalized.

According to PHAC, investigators identified E. coli O157 to be responsible for this outbreak, “with the use of enhanced techniques”, that enabled them to rule out 2 other reported cases with similar gastrointestinal symptoms, as not being related to the outbreak strain. The food-source associated with the outbreak has not been identified yet, but further investigations are underway.

This is the second E. coli outbreak of 2015 in Eastern Canada, with the first occurring between March 13 and March 31 in Alberta, Saskatchewan, Ontario, and Newfoundland and Labrador; all the 13 cases that were reported had a matching genetic fingerprint of E. coli O157:H7.
According to PHAC report, exposure to contaminated leafy greens (including all varieties of lettuces, in addition to other green leafy vegetables such as kale, spinach, arugula, or chard) was identified as the possible source of the outbreak. However, CFIA could not identify a specific food product as the single source of the pathogen, which illustrates the challenges associated with food-source attribution in outbreaks.

Escherichia coli O157:H7, a Shiga toxin–producing E. coli (STEC) is the strain most commonly associated with outbreaks of bacterial gastrointestinal disease in the North America. The subpopulation most severely affected by the outbreaks have historically been young children, and the elderly, whereas in the latest Canadian outbreak discussed in this report, the majority of patients were young males (average age of 23); however, the report does not disclose the age distribution of the patients who were hospitalized due to the severity of their condition.

The most common routs of transmission of E. coli pathogen, leading to outbreaks are generally identified to be contaminated food, water (drinking, irrigation or swimming), and environment, as well as person-to person and animal-to-person contact (Turabelidze et al. 2013).

Analysis of outbreak data suggest that foods most frequently implicated in outbreaks in North America are ground beef, leafy green vegetables, and unpasteurized dairy products, as well as sprouts, unpasteurized apple cider, melons and other fruits, and salami (Neil et al. 2009). Therefore, the suggested association of the earlier outbreak to leafy green vegetables, is in line with the characteristics of outbreak food-sources in general.

guiltyNumerous studies have specifically examined the survival and growth of E. coli on leafy vegetables. For instance, Parker et al. (2011) demonstrated E. coli’s “ability to multiply in the phyllosphere of whole lettuce plants” on shredded and intact harvested lettuce leaves, due to an up-regulation of genes involved in oxidative and osmotic stress, which also make the bacteria more resistant to antimicrobials commonly used in the fresh-cut produce industry. Therefore, the food industry needs to implement more effective strategies in handling raw vegetables.

Examining the timeline of PHAC’s report on E. coli outbreaks, reveals that in both occasions, it took the agency over two months from the time of the first reported case, to come to a final conclusion about the strain and possible food source. A similar timeline can be observed in E. coli outbreaks from previous years as well (2012 and 2013). The use of new and improved methods, such as Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF)-Based Peptide Mass Fingerprinting, as suggested by Chui et al.(2015) can contribute to a more rapid identification and fingerprinting of the pathogen, which can in turn, reduce the burden of outbreaks by early targeting of the attributed food source.

How can we, as consumers, prevent outbreaks from happening? How do you evaluate the effectiveness of communication methods, and timeliness of response to outbreaks by PHAC?


Works Cited:

Neil, K. P., Biggerstaff, G., MacDonald, J. K., Trees, E., Medus, C., Musser, K. A., … & Sotir, M. J. (2012). A novel vehicle for transmission of Escherichia coli O157: H7 to humans: multistate outbreak of E. coli O157: H7 infections associated with consumption of ready-to-bake commercial prepackaged cookie dough—United States, 2009. Clinical infectious diseases54(4), 511-518.

Parker, C. T., Kyle, J. L., Huynh, S., Carter, M. Q., Brandl, M. T., & Mandrell, R. E. (2012). Distinct transcriptional profiles and phenotypes exhibited by Escherichia coli O157: H7 isolates related to the 2006 spinach-associated outbreak. Applied and environmental microbiology78(2), 455-463.

Turabelidze, G., Lawrence, S. J., Gao, H., Sodergren, E., Weinstock, G. M., Abubucker, S., … & Tarr, P. I. (2013). Precise dissection of an Escherichia coli O157: H7 outbreak by single nucleotide polymorphism analysis. Journal of clinical microbiology51(12), 3950-3954.