E. coli Outbreaks Linked to Leafy Greens on the Rise


As health authorities in three states work with the CDC to determine the source of the E. coli O145 outbreak in Michigan, Ohio, and New York, a new outbreak database shows that E. coli outbreaks are not just sourced to meat.

“E. coli outbreaks associated with leafy greens such as lettuce are by no means a new phenomenon,” food safety advocate and attorney Bill Marler said on his blog. “Many might remember the spinach outbreak in 2006, which sickened more than 200 people, but the FDA has reported that in the last 12 years, 22 E. coli outbreaks have been linked to consumption of contaminated leafy greens, and more than 700 consumers have been made ill—some gravely so.”

E. coli is often contracted by consuming food or beverage that has been contaminated by animal (especially cattle) manure. The majority of foodborne E. coli outbreaks have been traced to contaminated ground beef; however the Center for Science in the Public Interest reports that fully 25 percent of E. coli outbreaks (1990-1998) were sourced to leafy greens. Leafy vegetables such as lettuce and spinach can become contaminated in fields or during processing when E. coli bacteria enter agricultural water, dirt, or even air (as dusty clouds from animal lots can contain particles of manure.)

Toxic E. coli strains like O157:H7 and O145 are a minority in the hundreds of strains of the bacterium Escherichia coli. Most strains of E. coli are harmless and live as normal flora in the intestines of healthy humans and animal. The E. coli bacterium is among the most extensively studied microorganisms. The combination of letters and numbers in the name of the E. coli O145 refers to the specific markers found on its surface and distinguishes it from other types of E. coli. The testing done to distinguish E. coli O145 or O157:H7 from its other E. coli counterparts is called serotyping. Pulsed-field gel electrophoresis (PFGE), sometimes also referred to as genetic fingerprinting, is used to compare E. coli isolates to determine if the strains are distinguishable.

E. coli was first recognized as a pathogen in the wake of the deadly outbreak of E. coli O157:H7 at Jack in the Box restaurants in the Pacific Northwest (1993). In the ten years that followed there were approximately thirty outbreaks recorded in the United States. This number is likely misleading, however, because E. coli O157:H7 infections did not become a reportable disease in any state until 1987 when Washington State became the first state to mandate its reporting. As a result, only the most geographically concentrated outbreak would have garnered enough notice to prompt further investigation.

With improved science and reporting, more non-O157 E. coli outbreaks are being reported. In 2008, more than 300 people fell ill and one lost his life in an outbreak of E. coli 0111 traced to an Oklahoma restaurant. The current outbreak in Michigan, Ohio, and New York is E. coli O145. Bill Marler has petitioned the USDA to add these strains and four others to the list of official adulterants, so that they can be tested for and prevented from entering the food supply.

“I’ve worked in foodborne illness for 17 years now,” said Marler. “I know how hard our public agencies are working to quickly trace illnesses to a vehicle, I expect that within a few hours one of the sources of this E. coli O145 outbreak will be announced.”