Abstract
Genomic characterization of an Escherichia coli O157:H7 strain linked to leafy greens–associated outbreaks dates its emergence to late 2015. One clade has notable accessory genomic content and a previously described mutation putatively associated with increased arsenic tolerance. This strain is a reoccurring, emerging, or persistent strain causing illness over an extended period.
Escherichia coli O157:H7 is estimated to cause ≈63,000 domestically acquired foodborne illnesses and 20 deaths in the United States each year (1). E. coli O157:H7 infections are typically associated with abdominal cramps, bloody diarrhea, and vomiting; however, a rare but serious condition called hemolytic uremic syndrome can develop, resulting in anemia and acute renal failure. Healthy cattle serve as the main reservoir for E. coli O157:H7, and contaminated food, water, and environmental sources, as well as contact with animals, have been the source of outbreaks of E. coli O157:H7 infections.
More recently, contaminated leafy greens have been recognized as a major source of E. coli O157:H7 illnesses and outbreaks. In foodborne illness attribution estimates for 2020 based on outbreak data, 58.1% of E. coli O157:H7 illnesses were attributed to vegetable row crops, a category that includes leafy greens (https://www.cdc.gov/foodsafety/ifsac/annual-reports.html). During 2009–2018, a total of 32 confirmed or suspected outbreaks of E. coli O157:H7 infections linked to contaminated leafy greens occurred in the United States and Canada (5).
A large E. coli outbreak in late 2019, hereafter referred to as outbreak A, caused 167 cases, hospitalized 85 persons from 27 states, and was associated with the consumption of romaine lettuce from Salinas Valley, California, USA (https://www.cdc.gov/ecoli/2019/o157h7-11-19/index.html). We characterized isolates from outbreak A and highly related isolates by using a variety of molecular methods.
FoodWorld 