Lessons Learned from a Decade of Investigations of Shiga Toxin-Producing Escherichia coli Outbreaks Linked to Leafy Greens, United States and Canada

Abstract

Shiga toxin-producing Escherichia coli (STEC) cause substantial and costly illnesses. Leafy greens are the second most common source of foodborne STEC O157 outbreaks. We examined STEC outbreaks linked to leafy greens during 2009-2018 in the United States and Canada. We identified 40 outbreaks, 1,212 illnesses, 77 cases of hemolytic uremic syndrome, and 8 deaths. More outbreaks were linked to romaine lettuce (54%) than to any other type of leafy green. More outbreaks occurred in the fall (45%) and spring (28%) than in other seasons. Barriers in epidemiologic and traceback investigations complicated identification of the ultimate outbreak source. Research on the seasonality of leafy green outbreaks and vulnerability to STEC contamination and bacterial survival dynamics by leafy green type are warranted. Improvements in traceability of leafy greens are also needed. Federal and state health partners, researchers, the leafy green industry, and retailers can work together on interventions to reduce STEC contamination.

Keywords: Canada; E. coli; STEC; Shiga toxin–producing Escherichia coli; United States; bacteria; disease outbreaks; enteric infections; food safety; leafy greens; vegetables.

Figure 1

Number of Shiga toxin–producing Escherichia coli outbreaks (n = 40) linked to leafy greens in the United States, Canada, or both countries, and all outbreak-related illnesses (n = 1,212), by year of first illness onset, 2009–2018.

Figure 2

Outbreak-related Shiga toxin–producing Escherichia coli illnesses (n = 1,124) linked to leafy greens, by isolation date, outbreak, and vehicle, United States and Canada, 2009–2018. Data on isolation date were available for 1,124 (98%) of 1,146 laboratory-confirmed illnesses. Illness onset date was not systematically collected for each case. Each color represents a different outbreak. *During these years, each season started 1 week earlier.

Figure 3

Outbreak-related Shiga toxin–producing Escherichia coli laboratory-confirmed illnesses (n = 1,124 illnesses for which information was available) and food (n = 8; spinach, romaine) and environmental isolates (n = 86; soil, water, sediment, scat) linked to leafy greens, by week of isolation, United States and Canada, 2009–2018.