By Dominika Trzilova
Tacos are on tonight’s dinner menu, so you go to the grocery store to pick up a few items, including romaine lettuce. You arrive at the produce section, but the lettuce display case is empty. Where happened? Was there a scorching heat wave? Or a shortage of farm workers to pick the produce? Neither is actually the case. Let me introduce you to Escherichia coli (or E. coli for short) as the ‘source’ of your troubles.
On November 20th, the Centers for Disease Control and Prevention (CDC) reported the most recent multi-state outbreak of disease linked to romaine lettuce contaminated with E. coli O157:H7. At the time, CDC advised consumers to refrain from eating lettuce and urged restaurants and retailers to stop selling romaine until further examination was completed. An update issued by the CDC along with the Food and Drug Administration on November 26th identified a specific region of California linked to E. coli contamination. It was now safe to eat romaine, as long as it did not come from the affected region. Crisis averted, right?
Not quite. Let’s dive a little deeper into some of the issues the recent outbreak raised. There has been a significant number of outbreaks linked to E. coli over the past few years. For example, you may remember that Chipotle had to close some of its restaurants in November 2015 due to an outbreak of disease caused by E. coli. In 2018 alone, CDC reported three outbreaks linked to E. coli O157:H7 – two affecting romaine lettuce (April-June and the most recent outbreak) as well as contamination of ground beef in July. All together, these resulted in 271 reported cases (of which 253 were associated with romaine consumption) and 6 deaths (note: accurate at the time of writing). Is eating salad no longer a good strategy for staying healthy? Hold on.
While poisoning by E. coli can be prevented by sufficient heat treatment (such as cooking meat thoroughly), lettuce is generally served raw. Unfortunately, washing your produce is not an efficient way to get rid of E. coli or other bacteria. That explains the CDC’s warning to refrain from eating romaine lettuce, because other than grilled romaine, most people do not cook their salad prior to consumption. While this may leave you thinking that the best way to avoid a hospital stay might be skipping salad, contaminated produce accounts for a negligible fraction of the total production. Furthermore, a large majority of people who consume contaminated produce will experience mild symptoms or no symptoms at all. Don’t give up on salads for the wrong reasons.
E. coli has been mentioned extensively throughout this article. But not all E. coli is harmful and will leave you with a stomach ache. There are thousands of ‘types’, also called strains, of E. coli. All humans have E. coli in our gut to help us digest food. Other kinds of E. coli are used in biomedical research to improve our understanding of different types of bacteria.
However, while some strains of E. coli are harmless, E. coli O157:H7 is not. Ever wondered what those numbers and letters represent? All bacteria have proteins on their surface that can trigger an immune response; these are called antigens. O and H are two of these antigens, found on the body and the flagella (tail) of E. coli, respectively. The numbers represent a type of an antigen based on when it was discovered. So the type of E. coli that caused the latest romaine lettuce outbreak had the 157th type of O antigen and 7th type of H antigen. This further underscores the diversity of E. coli strains. Cool right? E. coli O157:H7 is sometimes also referred to as enterohemorrhagic E. coli because it can cause diarrhea or hemorrhagic colitis in humans. In rare cases, infection can proceed to hemolytic uremic syndrome, which may result in acute renal failure and can be fatal.
So should you eat romaine? The decision is ultimately up to you. However, in my opinion, the benefits of eating romaine (such as such increasing your intake of nutrients such as fiber, folate, and vitamin K) still outweigh the risks. There will always be E. coli – inside us and around us, but the fact is, most strains of E. coli are completely harmless. So go ahead – fill that shopping cart full of romaine, and enjoy some fresh, crunchy romaine on top of your tacos! Happy eating!
Peer-reviewed by Leah Chapman