Parasitic Protozoa on Fruits and Vegetables


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An oocyst of Cyclospora cayetanensis as seen in a microscopic preparation: Image courtesy of the U.S. CDC

Wash Fresh Fruit and Vegetables

The foods most likely to transmit parasitic protozoa have one thing in common: they are often eaten raw. The results of the Health Canada study highlight the importance of thoroughly washing these vegetables under clean running water, even if they are sold as pre-washed greens.

Packaged, ready-to-eat salad greens are the ultimate in convenience for busy people. No doubt they result in the addition of many a healthy salad to meals that would otherwise have none. But the terms pre-washed and ready-to-eat clearly don’t necessarily guarantee that disease-causing organisms are not present. Washing again adds an extra measure of safety.

Sadly, no amount of washing will remove all of these parasites: they are simply too small and too easily lodged in the crevices and creases of plant material. When they’re present in produce, the best we can hope for is that washing will leave too few organisms behind to cause illness.

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Should We Give Up Salad?

The Health Canada study did not confirm that the organisms detected were actually alive and capable of causing illness. The authors note, however, that no outbreaks of illness were associated with any of the tested products and there were no recalls. (Study results were not available until after the products had all been consumed; therefore, this study did not trigger recalls.) Apparently, viable organisms were not present in sufficient numbers to cause clusters of cases, which is somewhat encouraging.

Eating has always had its risks, and today the food supply is generally safer than it’s ever been because of food safety regulations. Distressing as outbreaks of these parasitic infections are, the dietary benefits of fresh raw fruits and vegetables likely still outweigh the risks for most people.


CDC. Foodborne Outbreak Online Database (FOOD). Accessed March 26, 2013.

Dixon B, Parrington L et al. Detection of Cyclospora, Cryptosporidium, and Giardia in Ready-toEat Packaged Leafy Greens. (2013). Journal of Food Protection. 76(2):307-13. doi: 10.4315/0362-028X.JFP-12-282.

Drisdelle R. Parasites: Tales of Humanity’s Most Unwelcome Guests. (2010). Berkeley: University of California Press.

Health Canada. Food and Nutrition. Accessed March 26, 2013.

USDA Center for Nutrition Policy and Promotion. Choose MyPlate: 10 Tips to a Great Plate. (2013). Accessed March 26, 2013.

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