Why washing your fruit and vegetables won’t save you from the parasite causing ‘watery diarrhea’

Imported herbs, such as basil and cilantro, have been linked to outbreaks of cyclosporiasis in the past. Photo by Scott Olson/Getty Images

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The gastrointestinal disease that has reportedly sickened thousands in more than half of U.S. states could possibly be in Canada, but there hasn’t been an outbreak because we’re not detecting it, says a Canadian food safety expert. Though Canadian public health officials haven’t noted an increase in cases of cyclosporiasis, “it could be an ‘if you don’t look, you don’t find’ sort of thing,” says Keith Warriner, a professor at the University of Guelph’s department of food science.

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“To say that we’re protected in Canada, I’m not sure that’s quite true for the simple reason that when you get non-travel-related cyclospora, that must mean it’s a food vehicle,” says Warriner. “We could say, ‘Well, it must be strawberries. It must be raspberries. It must be herbs, like basil and cilantro,’ but no one’s actually able to identify that yet (in the U.S.). And for all we know, we could have multiple outbreaks going on at the same time.”

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Imported berries, herbs and pre-packaged salad mix have been linked to outbreaks of cyclosporiasis, but any produce in contact with people or sewage could be a vehicle. “Even oysters,” says Warriner.

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Washing with water, while a sound food safety practice and effective at removing debris, insects and pesticides, “doesn’t really cut it” with pathogens such as Cyclospora, E. coli and Salmonella, says Warriner. He notes that it takes 100 to 500 cyclospora oocysts to cause illness. “To give you perspective, you can get 50,000 oocysts on a needle pinhead. (Washing) is not going to do that much.”

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There’s a theory that the Cyclospora oocysts — the infectious stage of the microscopic parasite — “are extra sticky,” so they adhere to fresh produce and are carried along. “The thing about the oocysts is that they’re super tolerant,” says Warriner. They can withstand bleach, various sanitizers and even wastewater treatment.

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Cooking and freezing (at -20 degrees Celsius for roughly seven days), however, can neutralize them, which doesn’t suit all purposes. Seeking “a firewall” between the source and the consumer, Warriner developed a hydroxyl radical technology that uses hydrogen peroxide, UV light and ozone to inactivate parasites on soft fruit and vegetables.

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A cyclosporiasis outbreak has now reportedly sickened more than 3,000 people in 31 U.S. states, causing “watery diarrhea,” nausea and fatigue. The Centers for Disease Control and Prevention said it had received reports of 843 confirmed cases of the food- and waterborne intestinal illness, and was aware of more than 1,500 requiring further analysis. The source is still under investigation, and no deaths have been reported.

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The Public Health Agency of Canada (PHAC) said in an email to National Post last week that it “is not currently investigating any Cyclospora outbreaks.” Cyclosporiasis, a gastrointestinal disease caused by the parasite Cyclospora, is most common in tropical and subtropical regions.

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Though the parasite isn’t commonly found on food or in water in Canada, PHAC noted that domestic cases increase in spring and summer as people eat more imported fruit and vegetables.