I’m a food safety expert — these food products pose the greatest E. coli risks

This will make your stomach churn.

As dozens of people are sickened by E. coli in an outbreak linked to McDonald’s Quarter Pounder, food safety experts are finding out which items to avoid to avoid foodborne illness in grocery stores.

At the top of the list are bagged, pre-washed greens.

Barbara Kowalcyk, director of the Institute for Food Safety and Nutrition Security at George Washington University, told NBC News that produce that claims to be pre-washed — such as lettuce, vegetables or even cut fruit — should be avoided, as they can be a breeding ground for bacteria.

Instead, she recommends buying whole heads of lettuce and washing it yourself with water and drying it with paper towels.

“Any leaves that are torn or damaged, I just throw them away because that’s how bacteria can get in there,” she explained, adding that she also avoids sprouts and melons. “And I usually remove the outer leaves and throw them away.â€

The cantaloupe’s meshy skin can trap bacteria, added Darin Detwiler, a professor of food regulatory policy at Northeastern University.

“It’s one of the deadliest productions out there, of all things,” he told NBC News. “The pulp has a perfect pH and you can’t clean the outside enough.”

Don Schaffner, a professor of food science at Rutgers University, warned that most fruit — especially if it’s been sitting outside for long periods of time — also poses a risk.

“I do a lot of workshops, and they often have cut fruit on the breakfast buffet, and that fruit sits there all day,” he told NBC News. “We’ve done research to show that its physical appearance doesn’t change, but it can grow bacteria like nobody’s business.”

According to the Centers for Disease Control and Prevention, symptoms of food poisoning from bacteria such as listeria or E. coli — which cause infections in the gastrointestinal tract — include nausea, vomiting, fever, abdominal pain and diarrhea. Some cases can even result in hospitalization or be fatal.

Now, a McDonald’s E. coli outbreak has killed one person in Colorado and spread to multiple states, after the fast-food chain’s supplier recalled yellow onions “out of caution,” prompting other restaurants to do the same.

Schaffner explained that the more food is processed from the farm to your table, the more risk there is for it to be introduced to bacteria, which can then make you sick.

“The more rigging you do, of course the more places there are for things to go wrong,” he said.