PARSLEY very often is a garnish that is left on the plate. Which makes the discovery that parsley was responsible for seven outbreaks of shigellosis, a food-borne illness, last summer all the more remarkable.
''Parsley is one of those things you hardly ever ask about,'' said Dr. Robert Tauxe, the chief of the food-borne and diarrheal diseases branch of the Centers for Disease Control and Prevention in Atlanta. But scientists were able to link the outbreaks by using Pulsenet, a sophisticated detection system that enables them to fingerprint the DNA of bacteria. They can then compare the fingerprints to see if the bacteria are from a common source. In this case, they were then able to trace the parsley to a farm in Mexico.
Scientists at the Minnesota Health Department used Pulsenet to track the shigella bacteria that caused two of the outbreaks of shigellosis, which occurred in the state. From there, the system helped link the parsley to outbreaks in California, Massachusetts and Florida, and Ontario and Alberta.
The 493 confirmed and likely cases of shigellosis in this instance were traced to restaurant foods, including chicken sandwiches and pasta dishes, garnished with parsley.
Shigellosis, which occurs within 12 to 24 hours and lasts three to five days, causes fever, serious abdominal cramps, nausea and diarrhea. In the past it has been easily treated with antibiotics, but this strain from Mexico was more antibiotic-resistant and required additional treatment.
Some forms of shigella, generally found in developing countries, can cause dysentery, which may lead to kidney failure and death.
Between 15,000 and 20,000 cases of shigellosis are diagnosed each year in the United States, but the Centers for Disease Control say that like all food-borne infections, many more go undiagnosed.
Shigella lives in human feces and usually is passed from person to person when carriers do not wash their hands. But scientists believe this parsley was first contaminated at the farm right after it was harvested, when it was kept in water that had not been chlorinated. And the way the parsley was handled at the restaurants was a contributing factor. It was chopped and left at room temperature instead of being refrigerated. Chopping releases nutrients that feed the bacteria, but refrigeration lowers the level of the bacteria.
Parsley can be chopped in advance, after washing under cold running water. But chopped or whole, it should be refrigerated at all times.