Think your pre-washed lettuce is clean? Think again.
Canadian researchers tested the cleanliness of pre-washed salads and leafy greens and found parasites — one of them which is found in infected human feces — in dozens of samples from Ontario.
In the first large-scale study of its kind, researchers from Health Canada and the Public Health Agency of Canada examined 544 samples of store-bought, pre-washed lettuce purchased between April 2009 and March 2010 in the Waterloo, Ont. area, and found that nearly 10 per cent of the samples contained one of three parasites: cyclospora, cryptosporidium or giardia.
Their findings were published in the Journal of Food Protection.
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These parasites often originate in animal feces that then find their way into the water supply.
Cyclospora, however, is a human-borne parasite, found naturally in the intestine.
"Cyclospora is spread when people eat or drink food or water that has been contaminated with infected feces," Health Canada reports.
Not washing hands after using the washroom or changing a diaper is a common way to spread the parasite.
While cryptosporidium has previously been found in apples and locally-grown spinach, this is the first study to identify parasites cyclospora and giardia in North American produce.
Nine of the samples tested positive for cyclospora. Thirty-two samples tested positive for cryptosporidum, and 10 tested positive for giardia.
Of the 544 bags of greens purchased, 507 of them were grown in the U.S., with 46 of those found to be contaminated. Of the 23 samples from Canada, three were contaminated. Three Mexican samples were free of parasites.
"In the present study, a relatively high prevalence of all three parasites was found in packaged, ready-to-eat leafy greens," the researchers write.
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"This, along with the fact that all isolates tested represented species and genotypes commonly reported in humans, suggests that there is a potential for transmission to consumers, particularly since these leafy greens are typically consumed raw."
None of the products tested have been linked to any reported illness outbreaks, CTV News reports.
The study doesn't identify how the greens became contaminated. Researchers speculate contamination could be an equipment issue, a harvesting issue, a contaminated water issue or a food-handlers issue, among other possibilities.
And while washing your pre-washed greens can help lower the risk of transmission, even washing isn't a perfect strategy.
"The fact (the parasites) are there at all is of some concern to us," Brent Dixon, a parasite scientist with Health Canada, tells CTV News, adding all the samples tested were labelled as either pre-washed or triple-washed.
"Consumers that are concerned can do additional washing, but from what we know (additional washing) does not remove 100 per cent of pathogens from produce."
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However, this doesn't necessarily mean that we should ditch salads.
Dixon explains that the health benefits of raw greens still outweigh the potential risks.
For the ill, elderly and pregnant, the best lettuce strategy is to purchase intact lettuce, not the pre-cut products that have undergone more processing and, subsequently, are more likely to contain parasites.
Pregnant woman need to be especially careful with pre-washed salads.
According to BabyCenter, "If you store pre-washed salad in a warm room, or leave it until after its best-before date, bacteria, parasites, or viruses can form. If you then eat the contaminated salad, you're at risk of getting listeriosis. This only causes mild flu-like symptoms for you, but it can cause serious health problems for your baby. It can even lead to miscarriage, or the loss of a baby at birth."
The toxoplasma parasite, which can result from cat droppings decomposing in soil, is also dangerous for pregnant woman. While the risks of getting listeriosis and toxoplasmosis are small, it never hurts to be careful and wash that lettuce thoroughly.
Watch the video below to learn about how leafy greens are one of the top sources of food poisoning.