Pathogens On Produce And How Best To Avoid Them

Food poisoning from vegetables is just as serious as food poisoning from meats and dairy. Here are some things to look out for.


Bacteria, viruses, and parasites on fresh produce have potential to cause life threatening illnesses.  With fruits and vegetables coming from all corners of the world, contamination can occur at various points on the distribution chain.

The ongoing Salmonella outbreak in cucumbers, along with other past foodborne outbreaks in lettuce, berries and sprouts, highlight the need to practice food safety when preparing and cooking fresh fruits and vegetables.

Food Poisoning from Cucumbers

In late September of 2015, the Centers for Disease Control and Prevention (CDC) reported a total of 671 people in 34 states were infected with Salmonella poona from the latest outbreak in contaminated Mexican cucumbers. Three people have died and 133 were hospitalized. Public health investigators traced the source of the illnesses to cucumbers imported from Baja, Mexico. Read more about the outbreak here.

Food Poisoning from Lettuce

Rita Bernstein of Wilton, Connecticut, served mixed, pre-washed lettuce to her daughter Haylee, then three years old. That salad almost blinded the child.

The lettuce—which sickened 60 others in New York, Illinois, and Connecticut—was contaminated with E. coli O157:H7. After visiting the California farm where it was grown, investigators weren’t surprised.

The workers who picked the lettuce washed it in water that came from wells near cattle pastures, and no one had added chlorine to the water to kill any bacteria.

“They picked the lettuce and dunked it in a bath of cold water— called a hydrocooler—to cool it down quickly,” says the CDC’s Robert Tauxe. “In a big, centralized food supply, that’s how one dirty hand or manure run-off on a few heads of lettuce spreads to thousands and thousands of heads going all over the country. If the bath is contaminated, it spreads to all of the produce.”

To reduce the incidence of food poisoning from vegetables, California now makes sure that only clean water is used in the hydrocoolers on its produce farms, says Tauxe. But that didn’t stop an outbreak of another bacteria, Shigella, in parsley from a farm in Baja California, Mexico.

“The hydrocooler was using water from the local village water supply, which wasn’t chlorinated,” he explains. “In fact, the farmworkers got bottled water as part of their contract so they wouldn’t have to drink the local water.”

Says Tauxe: “If the food industry is going to wash produce that I’m going to eat without cooking, I want them to use water that I would drink.”

Food Poisoning from Sprouts

The Kroger supermarket chain doesn’t sell raw bean sprouts any more because they are too often contaminated with disease-causing bacteria. Wal-Mart stopped selling sprouts in 2011.

“There have been at least 35 outbreaks from contaminated sprouts since the mid-1990s,” says the Food and Drug Administration’s Michelle Smith. The primary culprits: Salmonella and E. coli.

Unsprouted seeds can be contaminated by dirty water, animals, or improperly composted manure in the field or during distribution or storage. A single Salmonella bacterium on a seed can easily grow to an infectious dose during the two to seven days it takes for the seed to sprout, notes the FDA.

“Rinsing the sprouts can remove dirt and some bacteria, but not the bacteria that have become firmly attached,” says Smith. “In the nutrient-rich, wet environment that sprouts are grown in, bacteria can enter root hairs and other plant structures where they can’t be washed off.” The only way to kill any bacteria that may be present is to stir-fry, boil, or thoroughly cook sprouts in some other way.

So, if you eat sprouts, make sure they’re thoroughly cooked, not added at the end for crunch.

Food Poisoning from Berries

Strawberries, raspberries, blackberries, and other berry products have caused 25 outbreaks with more than 3300 illnesses since 1990.

In 1997, over 2.6 million pounds of contaminated strawberries were recalled after thousands of students across several states reported illnesses from eating frozen strawberries in their school lunches. Hepatitis A was the culprit, and contamination may have occurred through an infected worker at a farm in Baja California, Mexico.

That same year, raspberries imported from Guatemala and Chile were implicated in an outbreak of Cyclospora across five states. Most of these illnesses, affecting 2700 consumers, were caused by Cyclospora in berries. The resulting infection is a parasitic illness of the intestines, which can cause severe diarrhea, dehydration, and  stomach cramps. Importantly, the illness does not resolve itself without antibiotics, thus requiring a trip to the doctor.

How to prevent food poisoning from vegetables and fruits:

  • Before you cut cantaloupes or other melons, scrub the skins with water and a brush. (If you don’t, cutting them could transfer pathogens from the rind to the flesh.)
  • Wash berries and other non-scrubbable fruits and vegetables with fast-running water. The friction of the running water helps remove bacteria. That’s better than soaking.
  • Wash fruit even if you plan to peel it. If there are microbes on the peel, they can contaminate the rest of the fruit when you peel it.
  • Eat only cooked sprouts (including home-grown).
  • Ask restaurants not to add raw sprouts to your sandwich or salad.

Should you wash bagged greens that say “washed” on the label?

“No. Rewashing bagged salad greens that were washed before being packaged is very unlikely to create a safer salad,” says Food and Drug Administration produce-safety expert Michelle Smith. “Once disease-causing bacteria become attached to leafy greens, it’s difficult to remove them by rinsing with water.”

In fact, “the greater likelihood is that you’ll make a safe product unsafe because of cross-contamination with bacteria from your fingers, cutting boards, countertops, or the sink,” adds Smith.

If the bag doesn’t say “washed,” though, you do need to wash the greens thoroughly.

Source: J. Glenn Morris, professor of infectious diseases and director of the Emerging Pathogens Institute at the University of Florida, and co-editor of Foodborne Infections and Intoxications. Other sources: Centers for Disease Control and Prevention, Food and Drug Administration, Marcus Glassman (Food Safety Project, Center for Science in the Public Interest).


For a complete guide on staying safe while shopping, preparing and cooking your food, check out From Supermarkets to Leftovers!