An E. coli outbreak that sickened at least 75 people and killed one is a reminder of the risk of contamination that can plague certain types of fresh produce, according to food safety experts.

The four professors said they themselves routinely avoid certain raw fruits and vegetables, such as sprouts, packaged lettuce and melon.

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 foodborne illness prevention, the news came as no surprise.

Don Schaffner, a food science professor at Rutgers University, said the more food is handled and processed on its journey from the farm to the restaurant or grocery store, the more opportunities there are to introduce or spread bacteria. This includes cutting, pre-washing or adding ingredients.

“Certainly the more you manipulate, the more opportunities there are for something to go wrong,” Schaffner said.

When fruits and vegetables are served uncooked, there is inherently no opportunity for bacteria to burn. This has contributed to previous food-related E. coli outbreaks, including an outbreak involving packaged baby spinach in 2006 that sickened over 200 people, as well as dozens of cases of E. coli and other foodborne illnesses linked to contaminated sprouts were brought. Cantaloupe melons are also contaminated with pathogens such as salmonella and listeria.

“If you just look at the sheer number of outbreaks and recalls over the last 15 years, we typically see more cases of E. coli associated with production,” said Darin Detwiler, a food regulatory policy professor at Northeastern University.

Although serious E. coli incidents in meat occurred 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 have been ongoing and a better understanding of the correct cooking temperatures required to kill the bacteria have reduced these cases.

Barbara Kowalcyk, director of the Institute for Food Safety and Nutrition Security at George Washington University's Milken Institute School of Public Health, said she tries to avoid eating packaged vegetables, sprouts and melons. Bags or containers containing lettuce or other leafy vegetables can trap bacteria and create an environment for them to multiply, she said. That's why she opts for heads of lettuce from the supermarket instead.

“Any leaf that’s torn or damaged, I just throw it away because that’s how the bacteria can get in,” she said. “And I usually cut off the outer leaves and throw them away.”

She then washes and dries the salad thoroughly.

“The key is running water and using a clean paper towel to dry,” she said. “The bacteria are kind of sticky and are removed by friction.”

Schaffner said previous E. coli outbreaks on pre-washed leafy greens were due to there not being enough chlorine in the water during rinsing. It's a different problem with sprouts, he said: The seeds are exposed to warm temperatures and when they germinate, they release nutrients into the water that enable bacteria to grow.

Cut melons, on the other hand, can be a common breeding ground for pathogens, especially if left outside.

“I do a lot of workshops and often there is sliced ​​fruit on the breakfast buffet, and the fruit just sits there all day,” Schaffner said. “We have conducted research to show that the external appearance does not change, but bacteria can grow that are no one’s business.”

Detwiler is especially careful to avoid melons because they have a webbed rind where bacteria can easily hide.

“It is, of all things, one of the deadliest foods of all,” he said. “Cantaloupe has a perfect pH and you can’t adequately clean the outside.”

E. coli spreads into the environment via animal or human feces and can contaminate food and water from there. Although significant improvements in agriculture have minimized the spread of pathogens in fields where produce is grown, experts say it is still important for consumers to consider the risk of E. coli — especially for young children, those over 65 and everyone with a weakened immune system. including those who are pregnant.

“This is a truly unique pathogen because the infectious dose is very low. So it can only take a few cells to make someone seriously ill,” said Kali Kniel, a professor of microbial food safety at the University of Delaware.

Food safety experts surveyed also said they avoid rare or undercooked meat, poultry, fish and eggs and don't drink unpasteurized milk.

Some also mentioned that they look for signs of cleanliness when eating at the restaurant.

“When I go to a restaurant I don't know, the first thing I do is go to the bathroom, because if the toilet looks terrible – like no one has cleaned it in a long time – then I don't even want to know what it's like kitchen looks,” said Detwiler.

However, fast-food restaurants generally are not hotbeds for foodborne illnesses, and Detwiler said McDonald's has a “long history of being a very leader” in food safety.

Kowalcyk agreed, adding that as a large chain, McDonald's likely has more procedures in place to train employees on contamination prevention.

“I don’t really think any particular type of restaurant would be riskier than others, except that large organizations tend to have a lot of resources and smaller organizations tend to have fewer resources or expertise,” she said.

According to the Centers for Disease Control and Prevention, there was previously no known connection between raw onions and an outbreak of this particular strain of E. coli. But in recent years, onions have been contaminated with pathogens: Salmonella outbreaks have been linked to this.

Kniel said she expects improvements due to the increasing number of E. coli cases.

“We learn something every time there is an outbreak,” she said.

For consumers concerned about E. coli, Schaffner acknowledged that it's impossible to avoid every item linked to foodborne illness.

“If you stop eating foods when they're associated with outbreaks, you don't have much choice in diet,” he said. “As a good friend of mine used to joke, the risks of not eating still outweigh the risks of eating.”