top of page

Why does lettuce keep getting contaminated by E.coli?

Updated: Jul 2, 2019

For the third time this year, the Public Health Agency of Canada is advising Canadians not to eat romaine lettuce, specifically in Ontario, Quebec and now New Brunswick, while health officials in the U.S. and Canada try to confirm the source of a new E. coli O157 outbreak.

So, why does lettuce keep getting contaminated by E.coli?

The answer is simple: from the way it is grown. Lettuce and other leafy greens need a lot of water to grow. So, it could be due to contaminated water, or due to cross contamination on the farm from animals and birds.

Another reason why salad ingredients like lettuce and cucumbers end up being the culprits of E.coli outbreaks is because we eat them raw. Many other vegetables can get contaminated by E.coli, but they rarely if ever cause E.coli outbreaks because the E.coli are killed during the process of cooking.

Washing your fruits and vegetables before consuming them is always a good idea, but unfortunately, it won't get rid of E.coli. In my opinion, pre-washed, pre-cut salads can actually harbour more bacteria because the bacteria can multiply faster when the salad ingredients are chopped and processed.

The Public Health of Canada website says that the following tips will help reduce your risk of an E. coli infection, but they will not fully eliminate the risk of illness.

1. Wash your hands thoroughly with warm water and soap for at least 20 seconds, before and after handling lettuce.

2. Unwashed lettuce, including whole heads of lettuce sold in sealed bags, should be handled and washed using these steps: Discard outer leaves of fresh lettuce.Wash unpackaged lettuce under fresh, cool running water. There is no need to use anything other than water to wash lettuce. Washing it gently with water is as effective as using produce cleansers. Keep rinsing your lettuce until all of the dirt has been washed away.

3. Don't soak lettuce in a sink full of water. It can become contaminated by bacteria in the sink.

4. Store lettuce in the refrigerator for up to seven days. Discard when leaves become wilted or brown.

5. Use warm water and soap to thoroughly wash all utensils, countertops, cutting boards and storage containers before and after handling lettuce to avoid cross-contamination.

6. Ready-to-eat lettuce products sold in sealed packages and labelled as washed, pre-washed or triple washed do not need to be washed again. These products should also be refrigerated and used before the expiration date.

How do you know if you have been infected by E.coli?

The following symptoms can appear within one to ten days after contact with the bacteria: nausea, vomiting, headache, mild fever, severe stomach cramps, watery or bloody diarrhoea.

Most symptoms end within five to ten days. There is no specific treatment for E. coli infections, other than monitoring the illness, providing comfort, and preventing dehydration through proper hydration and nutrition. Visit your doctor if you think you might have been infected by E.coli.

There are a lot of unanswered questions when it comes to why E.coli loves growing on lettuce, and how to prevent outbreaks. So, for the time being, just opt out from eating romaine lettuce.


Healthcare Consultant, in4MED


The author of this blog post is a Physician with over 10 years of experience working in the healthcare system as a clinician, researcher and educator. She is passionate about healthcare for older adults and strives to be a resourceful inspiration to caregivers.

*No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified healthcare professional.

61 views0 comments

Recent Posts

See All


bottom of page