E. Coli: What is it and Why is it Important?

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If you enjoy including Romaine lettuce in your salad, you’ve most likely noticed the empty spaces in the grocery store produce aisle where Romaine used to be found. The Centers for Disease Control and Prevention (CDC), the U.S. Food and Drug Administration (USDA), and public health and regulatory officials in several states are investigating a multi-state outbreak of dangerous Escherichia coli O157:H7 that has infected over 50 people from 16 different states. People first began to get sick  on March 13, 2018 and the CDC began their investigation on April 10, 2018.

So, What is E. Coli?

E. coli is a large group of bacteria that are found throughout our environment as well as within our own digestive system. E. coli was first identified by the German microbiologist and pediatrician Theodor Escherich when he studied the role of bacteria in the digestive tracts of infants in 1884.

Most strains of E. coli are harmless, but some types can lead to diarrhea, urinary tract infections, respiratory illness, or pneumonia. The strain of E. coli that is the most dangerous to humans is E. coli O157:H7, known as a STEC or ‘Shiga toxin-producing’ E. coli. STEC is most often found in the digestive tracts of cattle, goats, sheep, deer, and elk. STEC doesn’t make these animals sick, but it can cause human illness. Sometimes other types of animals, like pigs and birds, pick up STEC from the environment and can spread it in their feces.

STEC is especially dangerous because it can easily contaminate our food supply. Vegetables like Romaine lettuce can be contaminated via fertilizer and water, or through contact with livestock-associated birds. STEC can also be transmitted to humans via the fecal contamination of meat during butchering and packaging.

Why is STEC So Dangerous?

The Shiga toxin produced by STEC attacks small blood vessels inside our body, kills intestinal cells, and causes bloody diarrhea and severe abdominal pain. Sometimes people affected by STEC believe they have the flu and don’t seek treatment.

STEC can sometimes lead to hemolytic uremic syndrome (HUS), a potentially-deadly condition that can involve widespread blood clots and hemolytic anemia (the abnormal breakdown of red blood cells), thrombocytopenia (a lack of blood platelets which reduces the blood’s ability to form clots), and renal failure.

According to CDC data, the current E. coli outbreak associated with Romaine lettuce is the first this year. Since 2006, typically 2-3 outbreaks occur each year in foods including alfalfa sprouts, leafy greens, ready-to-eat salad, ground beef, cheese, and pre-packaged cookie dough.

What is the Cause of the Current Outbreak?

Investigators narrowed down the source of the E. coli O157:H7 bacteria to Romaine lettuce grown in Yuma, Arizona. Over 90% of the lettuce in your grocery stores during the winter months is grown in Yuma, in the southwestern corner of Arizona where the sun shines 350 days during the year. While we know the current E. coli outbreak occurred in Yuma, the exact source of the contamination has not yet been determined.

What Actions Should I Take Now?

The CDC recommends throwing out all uneaten Romaine lettuce, both whole heads of Romaine as well as bagged, chopped Romaine and salad mixes that contain Romaine lettuce unless you know for sure that it was not grown in Yuma. Since packaging labels typically don’t identify growing regions, if you’re unsure, it’s safest to throw out the lettuce. Restaurants and retailers should not sell or serve Romaine lettuce in any form unless they know for certain that it was not grown in Yuma. Romaine lettuce grown anywhere except Yuma is safe to eat.

If you have diarrhea that lasts for more than 3 days, or have diarrhea with high fever and bloody stools, or are vomiting and can’t keep down liquids, it’s important to contact your healthcare provider. Very young children, the elderly, and anyone with a chronic health condition should be especially vigilant and contact their healthcare providers immediately.

The CDC Recommends These 6 Steps to Prevent a STEC Infection:

  1. Wash your hands after using the bathroom, changing diapers, or before preparing food.
  2. Wash your hands after contact with animals in any location, including farms, petting zoos, fairs, or your own backyard.
    Cook meat thoroughly to an internal temperature of at least 160°F/70°C. It’s best to use a thermometer, as color is not a very reliable indicator of “doneness.”
  3. Do not drink unpasteurized milk, dairy products, or juices (like fresh apple cider).
  4. Avoid swallowing water when swimming or playing in lakes, ponds, streams, swimming pools, and backyard ‘kiddie’ pools.
  5. Prevent cross-contamination in your kitchen by thoroughly washing counters, cutting boards, and utensils after they touch raw meat.

The Bottom Line: While E. coli is potentially dangerous, there are steps we can take to prevent an infection. For now, substitute other types of dark green leafy plants like arugula, spinach, endive, or butter lettuce for Romaine so that you continue to enjoy the nutrition benefits of these foods.

By Lynn Grieger, RDN, CDE, CPT, CHWC


  1. Centers for Disease Control and Prevention. Multistate Outbreak of E. coli O157:H7 Infections Linked to Romaine Lettuce. https://www.cdc.gov/ecoli/2018/o157h7-04-18/index.html last updated 4-20-18. Accessed 4-24-18.
  2. Centers for Disease Control and Prevention. E. coli Questions and Answers. https://www.cdc.gov/ecoli/general/index.html last updated 2-26-18. Accessed 4-23-18.
  3. Blount ZD. The unexhausted potential of E. coli. eLife. 2015;4:e05826. doi:10.7554/eLife.05826.
  4. Centers for Disease Control and Prevention. Reports of Selected E. coli Outbreak Investigations. https://www.cdc.gov/ecoli/outbreaks.html last updated 4-20-18. Accessed 4-23-18
  5. Kurt D. Nolte, University of Arizona. Winter Lettuce Production, Yuma Arizona. https://www.cals.arizona.edu/fps/sites/cals.arizona.edu.fps/files/Lettuce%20Production%20Presentation.pdf Accessed 4-24-18.

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