August 19, 2022

What Do E. coli O157:H7 Outbreaks 2006-2020 Tell Us About New One?

Three days ago, the CDC announced a new five-state E. coli O157:H7 outbreak that is associated with unusually severe infections. Nine of the 16 people sickened have been hospitalized, three of them with hemolytic uremic syndrome (HUS) a form of kidney failure. One person has died.

The food source of the outbreak has not been identified yet, but health officials do know that the outbreak strain is the same one linked to the 2018 outbreak linked to romaine lettuce grown in Yuma, AZ that killed five people, and a deadly 2020 E. coli outbreak where leafy greens were a suspected source.

Both the U.S. Department of Agriculture’s Food Safety and Inspection Service (USDA FSIS), which regulates meat and poultry, and the U.S. Food and Drug Administration (FDA) which regulates all other foods are investigating the outbreak, according to a new update on the investigation from the Centers for Disease Control and Prevention (CDC).

We took a look at all of the multistate E. coli O157:H7 outbreaks announced by the CDC between 2006 and 2020 to see if they might shed some light on the likely food source of this outbreak.  Of the 28 outbreaks, beef was the most common food source, with seven outbreaks, followed by romaine lettuce with four outbreaks.

E.coli Lawyer - Chart of E.coli Outbreaks 2006-2020 by Food Source


A closer look at the information shows that salad greens accounted for 10 of the 28 outbreaks where a food source was identified and one of the outbreaks with a food source categorized as “unknown.” In that outbreak, all of the patients interviewed by health officials reported eating romaine, spinach and/or iceberg lettuce in the week before they became ill and the outbreak strain was identified in a sample of Tanimura & Antle brand romaine lettuce. The company issued a product recall.

“However, investigators were unable to determine if any ill people in this outbreak got sick from eating the recalled product. No one specifically reported eating Tanimura & Antle romaine lettuce, and some people got sick before the “packed on” dates for the recalled products.

FDA conducted traceback investigations and worked with state partners to conduct inspections at several farms. However, none of the findings identified a common source in the distribution chain or linked the farms to the outbreak,” the CDC stated in its final report on the outbreak.

Romaine is the Source of Most E.coli Outbreaks Linked to Leafy Greens

Of the 10 outbreaks where salad greens are implicated, just two have no association with romaine – one linked to spinach, the other linked to spinach and spring mix. In two outbreaks where the food source was identified as “salad kits” and “RTE (ready-to-eat) salads,” the contaminated ingredient was romaine. In each of the two outbreaks where “leafy greens” were identified as the source, more than half of the patients reported that one of the leafy greens they ate in the week before they became ill was romaine.  And the 2017 leafy greens outbreak occurred at the same time that the same E. coli strain was sickening people in Canada where the food source was identified as romaine.

In October 2020, the CDC published a study in its journal, Emerging Infectious Disease, called Lessons Learned from a Decade of Investigations of Shiga Toxin–Producing Escherichia coli Outbreaks Linked to Leafy Greens, United States and Canada. That research looked at 40 E. coli outbreaks linked to leafy greens between 2009 and 2018. Combined they resulted in 1,212 illnesses, 420 hospitalizations, 77 cases of HUS and eight deaths. Romaine was identified more often than any other leafy green in the study.

The study found that 63 percent of the people sickened in those leafy greens outbreaks were female. That’s consistent with the outbreaks on our chart that occurred after 2018 which range from 60 to 64 percent female. In the new outbreak, 14 of the 16 patients are female. They range in age from 10 to 95 years old. The number of cases from each state is: Arkansas (6), New York (1), Oklahoma (5), Virginia (2), and Washington (2). The fatality was reported in Washington.

Romaine, Leafy Greens Outbreaks are Recent, Interlinked

Seven of the outbreaks on the chart above plus two more that were combined with one of them have occurred since 2017. Each of them shares with another either the same strain, the same romaine lettuce grower, or both. So, most of the E. coli O157:H7 outbreaks linked to leafy greens have occurred since 2017, while all of the outbreaks linked to beef occurred before that year.

E. coli Lawyer - Bulletin Board of E. coli Outbreaks


Investigations Involving CDC, FDA and USDA FSIS

The CDC says it is working with state agencies, the FDA and USDA FSIS on the investigation of the new outbreak gathering three different kinds of information: epidemiologic which deals with patterns of illness, time frames, common food exposures; traceback, which uses records to identify a common point of contamination in the distribution chain; and food and environmental testing, which looks for the bacteria the sickened the patients in samples of food they have eaten.

Because FDA and USDA FSIS regulate different foods, usually just one of them works with the CDC and state partners on an outbreak investigation. But there have been two recent outbreaks where all three federal agencies collaborated – two E. coli O157:H7 outbreaks linked to salad kits containing cooked chicken where the romaine in the salad was found to be contaminated.  One of them, linked to Field Fresh Chopped Salad with Grilled Chicken and Mexicali Salad with Chili Lime Chicken, produced by Glass Onion Catering and sold at Trader Joe’s grocery store locations, occurred in 2013. The other was the 2019 Romaine E. coli O157:H7 outbreak that included packaged salads produced by Missa Bay of Swedesboro, N.J. and sold nationwide under the brand named Ready Pac.

Finally, it should be noted that cattle are the primary reservoir of E. coli O157:H7 and in a number of these investigations, the outbreak strain has been discovered in the feces of cattle grazing nearby the fields where these leafy greens are grown. In many cases, there aren’t buffer zones between cattle grazing areas and fields where produce is grown, and often the water used to irrigate the crops is untreated.

After each of these outbreaks, the FDA makes recommendations to growers such as “establish a buffer zone” and “treat water used to irrigate crops during the weeks closest to harvest,” said Food Safety Attorney and Food Poisoning Bulletin Publisher Fred Pritzker. “If we had laws instead of suggestions, maybe someone would listen.”


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