Outbreaks of Escherichia coli O157:H7 Infections Linked to Romaine Lettuce in Canada from 2008 to 2018: An Analysis of Food Safety Context

Abstract

Foodborne diseases are a major cause of illness in Canada. One of the main pathogens causing foodborne illnesses and outbreaks in Canada is Escherichia coli O157:H7.In Canada, from 2008 to 2018, 11 outbreaks of E. coli O157:H7 linked to leafy greens were identified, including 7 linked to romaine lettuce (63.6%), 2 linked to iceberg lettuce (18.2%) and 2 linked to other or unspecified types of leafy greens (18.2%). The consumption of lettuce in Canada, the behaviour of E. coli O157:H7 on lettuce leaves as well as the production practices used for romaine and iceberg lettuce do not seem to explain why a higher number of outbreaks of E. coli O157:H7 were linked to romaine compared to iceberg lettuce. However, the difference in the shape of iceberg and romaine lettuce could be an important factor.Looking at the 7 outbreaks linked to romaine lettuce in Canada between 2008 and 2018, an eastern distribution of cases was observed. Cases from western provinces were only reported twice. The consumption of romaine and iceberg lettuce by the Canadian population does not seem to explain the eastern distribution of cases observed but, the commercial distribution and the travel distance of lettuce as well as the storage practices used may be important factors.In the past 10 years, the majority of the outbreaks of E. coli O157:H7 linked to romaine lettuce happened during 2 time periods: in the spring between the months of March to June and in the fall between the months of September to December. The timing of these outbreaks may be explained by the lettuce availability in Canada, the growing region transition periods in the US and the seasonality in the prevalence of E. coli O157:H7. The consumption of romaine lettuce by the Canadian population does not to explain the timing of the outbreaks observed.

Comparative microbial analyses of hydroponic versus in-soil grown Romaine lettuce obtained at retail

“…Lettuce can be grown using different farming practices, including conventional or organic practices, using soil, or hydroponically, using a recirculated flowing film of nutrient solution ( Coulombe et al., 2020 ). The hydroponic farming method is a system in which growers cultivate plants without soil in a controlled environment ( Aires, 2018 ).…”

“…In most of these outbreaks, Salmonella , Shiga-toxin producing E. coli (STEC), and L. monocytogenes were the causative agents ( Callejón et al., 2015 ; Carstens et al., 2019 ). In Canada, E. coli O157:H7 was the main pathogen causing foodborne outbreaks linked to leafy greens ( Coulombe et al., 2020 ). Between 2008 and 2018, there were eleven E. coli O157:H7 outbreaks linked to leafy greens in Canada, including 7 associated with Romaine lettuce, 2 associated with iceberg lettuce, and 2 linked to other leafy greens ( Coulombe et al., 2020 ).…”

“…In Canada, E. coli O157:H7 was the main pathogen causing foodborne outbreaks linked to leafy greens ( Coulombe et al., 2020 ). Between 2008 and 2018, there were eleven E. coli O157:H7 outbreaks linked to leafy greens in Canada, including 7 associated with Romaine lettuce, 2 associated with iceberg lettuce, and 2 linked to other leafy greens ( Coulombe et al., 2020 ). Studies also confirm the connection between outbreaks in the U.S. involving STEC found in leafy greens ( Bottichio et al., 2020 ) and lettuce ( Taylor et al., 2013 ).…”

Consumption of High-Risk Foods in the Canadian Population, Foodbook Study, 2014 to 2015

“…Four foods were included because they were high risk for Salmonella contamination: raw or undercooked eggs, store-bought breaded chicken, melons, and tahini (7,29,49,75,76). Romaine lettuce was included because it is high risk for E. coli contamination (21). Six high-risk foods for Listeria contamination were soft cheeses, deli meats, hot dogs, pâté or meat spreads, smoked fish, and raw fish (45,62,66).…”

Seasonality, shelf life and storage atmosphere are main drivers of the microbiome and E. coli O157:H7 colonization of post-harvest lettuce cultivated in a major production area in California

“…EcO157 displays weak fitness as a plant colonist in field studies [ 25 – 27 ], although it has the ability to multiply in the lettuce phyllosphere under growth-permissive conditions in the laboratory [ 28 , 29 ]. Despite this low prevalence and poor fitness on lettuce crops, EcO157 has caused numerous outbreaks of disease attributed to lettuce in the USA, Canada and Europe [ 16 , 18 , 30 – 32 ]. Additionally, lettuce-associated outbreaks of STEC in the USA follow a seasonal pattern as infections occur more frequently from lettuce harvested in the fall on the West coast of California and in the late winter-early spring in the Southeastern part of California and in Arizona [ 33 , 34 ].…”