Lettuce Learn a Bit About E. Coli

By Diane Wright Hirsch, MPH

Senior Extension Educator/Food Safety

 

romaine lettuce
Photo: Wikimedia Commons

Recent news reports regarding the romaine lettuce outbreak have, yet again, raised concern about pathogens in our food supply. In particular, leafy greens continue to show up as a source for outbreaks. Two outbreaks since late fall have implicated romaine and/or leafy greens. In both outbreaks, E. coli O157:H7 was the culprit.

What exactly is E. coli?

Escherichia colior E. coliis a group of bacteria, some of which are harmless, and some of which are pathogenic, or disease causing. These bacteria are ubiquitous in the environment: they can survive in water, soil, on plants, and in the intestinal tracts of people and animals. Some types of E. colicause diarrhea, some cause urinary tract infections, and other may cause pneumonia or other diseases.

If you have a well, you are likely familiar with the term “generic E. coli.”  Generic E. coli(sometimes referred to as Biotype I), is found in the intestinal tracts of animals. Therefore, the public health and regulatory community use the presence of generic E. coliis an indicator that some type of fecal contamination (poop) is present. A test for generic E. colican determine if well water is drinkable, if food processing environments are clean, if meat is potentially contaminated with fecal matter or if irrigation water is safe to use on crops.

Generic E. coli, because it is found in fecal matter, may also indicate the potential for the presence of other pathogens that can be found in feces: bacteria such as Salmonellaand pathogenic types of E. coli; viruses such as hepatitis A or norovirus; and parasitic protozoa including Cryptosporidium parvum. All of these microorganisms have been associated with foodborne disease outbreaks.

While there are a number of pathogenic strains, it is Shiga toxin-producing E. coli(STEC) or enterohemorrhagic E. coli(EHEC) that is identified most often as a cause of foodborne illness. O157:H7 is one of several STEC strains. Hamburger, spinach, lettuce, sprouts, unpasteurized or “raw” milk and cheeses, unpasteurized fruit juice including cider, and  flour have all been identified as food sources in O157:H7 outbreaks.

This can be an awful disease. This type of E. coliproduces a Shiga toxin, which can be associated with more severe disease, including bloody diarrhea and hemolytic uremic syndrome (HUS), a type of kidney failure. The experience of an STEC infection can be different for each person. Contributing factors might include the age of the patient (very young or older people may have more severe infections due to compromised or undeveloped immune systems) and the general health of the person (again, if the immune system is already compromised, the disease may be more severe). However, a healthy adult can also experience more severe disease. Often, the symptoms include severe stomach cramps, diarrhea (often bloody), and vomiting. Again, the CDC states, “If there is fever, it usually is not very high (less than 101˚F/less than 38.5˚C). Most people get better within 5–7 days. Some infections are very mild, but others are severe or even life-threatening.”

Life threatening complications can occur when the Shiga toxin latches onto specific organs, such as the kidney. HUS can result in short term kidney failure or may result in long term disability, or even death.

How does E. coli get into our food?

We have been aware of the risk of E. coliin animal products for years. According to the Centers for Disease Control, “STEC live in the guts of ruminant animals, including cattle, goats, sheep, deer, and elk. The major source for human illnesses is cattle. STEC that cause human illness generally do not make animals sick. Other kinds of animals, including pigs and birds, sometimes pick up STEC from the environment and may spread it.”

It was likely the Jack in the Box hamburger related outbreak in 1993 that increased the awareness of both the public and the public health community of the relationship. After that outbreak, Rhode Island passed a law that does not allow restaurants to serve undercooked hamburgers to kids under 12 – a population that is at risk for the worst consequences of an E. coliinfection. At the same time, the recommended safe end-cooking temperature of hamburger was increased to 160 degrees F and sweeping regulation was passed that required meat and poultry processors, to develop food safety plans and be part of a food safety regulation program that included testing for generic E. coli,as well as pathogenic strains of the bacteria.

That makes sense to consumers. After all, if these pathogens are found in the intestinal tracts of animals and in fecal matter, then animal foods are most likely at risk for contamination.

So, how are fruits and vegetables contaminated with E. coli? As stated earlier, E. colican live in ruminants, including deer. Other wildlife may carry the bacteria after picking it up from the environment—the soil, dead animals, or contaminated water. The great outdoors is also the great toilet for these animals. Their feces end up in the soil and water or on the feed of birds or insects. Fruits and vegetables are grown in this soil. There is some risk of contamination as a result. Birds poop on tomatoes, apples fall on deer poop, etc.

Newer regulation target produce growers in an effort to reduce the risk for foodborne illness from fresh fruits and veggies. The Food Safety Modernization Act Produce Safety Rule includes requirements to test irrigation water, keep records of sanitation practices in the packing house, and employee training concerning personal hygiene and safe handling of produce.

Leafy greens continue to be associated with more outbreaks than other types of vegetables, with the exception of fresh sprouts. First, we eat them raw. There is no kill step to destroy pathogens. Second, they are leafy and grow close to the soil. If contaminated, those leaves can harbor and protect the bacteria. If lettuces are cut and then washed, the contamination can spread to greens that have not been contaminated, making the problem bigger. Once cut or chopped, the greens have even more open surface area that may allow the bacteria to internalize.

Like meat and poultry, any food product that is grown in the field will never be 100% risk free. The industry is hard at work doing what they can to reduce your risk.

So what should a consumer do?

First, do not stop eating greens, tomatoes, or other fresh fruits and vegetables. The benefits of a diet high in fresh produce far outweigh the risk of contracting a foodborne disease from them. Learn how to choose, store, prepare and handle them safely.

Purchase your produce from a farmer that has instituted good agricultural practices and good produce handling practices. If you buy from a local farmer at the farm or at a farmers’ market, ask the farmer if they have attended a food safety course or if they have a food safety program on their farm.

When buying fresh produce, avoid those that are bruised or cut if you are going to eat them raw.  Openings in the skin or bruises may increase the ability of bacteria or other microorganisms to reach the flesh of the fruit or vegetable. Refrigerate produce that should be refrigerated (leafy greens, scallions, broccoli, cucumbers) to minimize growth of microorganisms. In addition, refrigerate all cut produce.

Other food safety tips:

  • Wash all produce prior to eating.
  • Use clean knives, cutting boards, hands and other utensils when preparing raw lettuce for a salad or cutting a melon for breakfast.
  • Don’t cross contaminate ready-to-eat fresh produce with raw meat or poultry. I always prepare the salad first, then the meat for my meal.
  • Store raw, ready-to-eat produce to protect it from raw meat, poultry or fish.
  • Place the meat on a plate if it must be stored above the veggies. (I can never understand why produce drawers are under all other shelves in the fridge, making it a bit easier for meat juices to drip down onto the fresh produce.)

Some folks may want to consider purchasing heads of lettuce rather than chopped greens, though even whole heads of romaine were implicated in the most recent outbreak. If you do purchase pre-cut greens, make sure they are of good quality without a lot of browning or slimy leaves in the bag. If they are washed it is best not to rewash as you risk contamination during the process. However, if there are beginning signs of wilting or mushy leaves, I would wash, dry and store the remaining greens in the refrigerator, wrapped in a clean paper towel.

Continue to enjoy salads, fresh fruit and other veggies on a daily basis. It is an important part of a healthy diet. Just be sure to pay attention good safe food handling practices as you prepare to enjoy your meal.

For more information about food safety, visit our website at www.foodsafety.uconn.edu, check out some of the links in the article, or contact the Home and Garden Education Center at ladybug@uconn.edu or 1-877-486-6271.

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