Cryptosporidium in irrigation water can invade and be protected by spinach tissue, according to an article published in this month's Applied and Environmental Microbiology.
This protozoan pathogen, which the authors describe as "... an environmentally resistant, abundant, and ubiquitous human pathogen ..." has been found in 36% of irrigation waters used on crops that are typically eaten raw in the US and Central America.
Cryptosporidium became notorious in the United States in 1993, when it contaminated the drinking water supply in Milwaukee, WI and sickened an estimated 403,000 people. The microbe has been associated with waterborne outbreaks of gastroenteritis on numerous occasions both before and since the Milwaukee outbreak.
The pathogen also has been fingered in foodborne disease outbreaks – usually as a result of foodhandler contamination in a restaurant or foodservice facility. Occasionally, Cryptosporidium has contaminated fresh produce such as dropped apples used in apple cider. Unpasteurized cider was linked to a 1996 outbreak of Cryptosporidium in New England.
Now, spinach farmers – and spinach lovers – may face a more serious problem. If the results reported in Applied and Environmental Microbiology by USDA researchers are correct, Cryptosporidium oocytes (the reproductive form, equivalent to an egg) in irrigation water can attach firmly to spinach leaves in the field, and even enter the leaf tissue through the pores. Once inside, the oocytes are completely protected from vigorous washing and from disinfectants (such as chlorine).
It doesn't take many Cryptosporidium oocytes to infect a healthy person – 9 or 10 often are all that's needed. Some infected individuals will experience little or no discomfort. Others, especially those who are unusually susceptible to infection, may suffer from severe – even life-threatening gastroenteritis.
Cryptosporidium parvum-contaminated leafy produce could be the next major food safety problem. It is widespread, difficult to kill, and – because it can't be cultured in the lab – difficult to detect in foods.
Irradiation of leafy green produce might become our only option.
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