The Summary
- Amid the E. coli outbreak believed to be linked to onions served at McDonald’s, food safety experts say some types of fresh produce carry extra risk.
- Many avoid eating alfalfa or bean sprouts, as well as packaged salad greens and cantaloupe.
- Precut and prewashed produce can be especially risky, they said.
An E. coli outbreak that has sickened at least 75 people and killed one is a reminder of the risk of contamination that can plague certain types of fresh produce, food safety experts said.
The four professors said they routinely avoid certain raw fruits and vegetables, such as Brussels sprouts, bagged lettuce and cantaloupe.
Although the investigation is ongoing, federal officials suspect that pre-washed, sliced onions served raw on McDonald’s Quarter Pounders are the likely source of the E. coli outbreak. For those who specialize in preventing foodborne illness, the news came as no surprise.
Don Schaffner, a professor of food science at Rutgers University, said the more food is handled and processed on its journey from the farm to a restaurant or grocery store, the more opportunities there are to introduce or spread bacteria. That includes cutting, pre-washing or adding ingredients.
“The more handling you do, the more places there are for things to go wrong,” Schaffner said.
There is no natural way for bacteria to heat up when fruits and vegetables are served raw. This has contributed to previous E. coli outbreaks linked to produce, including a 2006 outbreak in prepackaged baby spinach that sickened more than 200 people and dozens of cases of E. coli and other foodborne illnesses linked to contaminated Brussels sprouts. Cantaloupe has also been contaminated with pathogens, including salmonella and listeria.
“If you just look at the number of outbreaks and recalls over the last 15 years, we tend to see more cases of E. coli linked to produce,” said Darin Detwiler, a professor of food regulatory policy at Northeastern University.
While there were serious E. coli incidents in meat decades ago — including an outbreak linked to Jack in the Box hamburgers that sickened hundreds of people and killed four in the early 1990s — changes in federal regulations and a better understanding of the proper cooking temperatures needed to kill the bacteria have reduced those cases.
Barbara Kowalcyk, director of the Institute for Food Safety and Nutrition Security at the George Washington University Milken Institute School of Public Health, said she does her best to avoid packaged greens, Brussels sprouts and melons. Bags or containers of lettuce or other leafy greens can trap bacteria and create an environment for them to multiply, she said, so for salads, she opts for lettuce heads from the grocery store instead.
“Any leaf that’s torn or damaged, I just throw it away, because that’s where the bacteria can get in,” she said. “And I usually take the outer leaves off and throw them away.”
She then washes and dries the lettuce thoroughly.
“The key is running water and using a clean paper towel to dry it,” she said. “The bacteria are a little sticky, and friction is what gets them off.”
Schaffner said previous E. coli outbreaks involving pre-washed greens have been caused by insufficient chlorine in the water when they were rinsed. Sprouts pose a different problem, he said: The seeds are exposed to warm temperatures, and as they sprout, they release nutrients into the water, allowing bacteria to grow.
Meanwhile, cut melons can be a common breeding ground for pathogens, especially if left lying around.
“I teach a lot of workshops, and they often have cut fruit on the breakfast buffet, and that fruit sits there all day,” Schaffner said. “We’ve done research to show that it doesn’t change the appearance of it, but bacteria can grow there like nothing.”
Detwiler is especially careful to avoid melons because of their web-like skin, which can easily hide bacteria.
“It’s one of the deadliest fruits and vegetables out there,” he said. “Cantaloupe has a perfect pH, and you can’t clean the outside enough.”
E. coli spreads through the environment via animal or human feces and can contaminate food and water from there. While significant improvements in agriculture have minimized the spread of pathogens in fields where fruits and vegetables are grown, experts said it’s still important for consumers to be aware of the risk of E. coli — especially for young children, people over 65 and anyone with a weakened immune system, including pregnant women.
“This is a really unique pathogen because there’s a very low infectious dose. So it can only take a few cells to make someone very sick,” said Kali Kniel, a professor of microbial food safety at the University of Delaware.
Food safety experts interviewed also said they avoid rare or undercooked meat, poultry, fish and eggs and don’t drink unpasteurized milk.
Some also said they look for signs of cleanliness when they eat out.
“If I go into a restaurant that I’m not familiar with, the first thing I do is go to the bathroom because if the bathroom looks horrible — like no one has cleaned it in a long time — I don’t even want to know what the kitchen looks like,” Detwiler said.
That said, fast-food restaurants are generally not hotbeds for foodborne illness, and Detwiler said McDonald’s has a “long history of being a very prominent leader” in food safety.
Kowalcyk agreed, adding that as a large chain, McDonald’s likely has more procedures in place to train employees on how to avoid contamination.
“I don’t really think any particular type of restaurant is riskier than others, except that large organizations tend to have a lot of resources and smaller organizations tend to have less resources or expertise,” she said.
According to the Centers for Disease Control and Prevention, raw onions have not been linked to an outbreak of this particular strain of E. coli. But onions have been contaminated with pathogens in recent years: Salmonella outbreaks have been linked to them.
Kniel said she expects improvements to be made as the number of E. coli cases grows.
“We learn something every time there’s an outbreak,” she said.
For consumers concerned about E. coli, Schaffner acknowledged that it’s impossible to avoid every item that has been linked to foodborne illness.
“If you stop eating foods that have been linked to outbreaks, you’re not going to have much left in your diet,” he said. “As a good friend of mine used to say, the risks of not eating them still outweigh the risks of eating them.”