State officials said Monday an outbreak of cyclosporiasis that has sickened more than 2,600 Michigan residents is believed to have originated with infected lettuce or salad greens.

Health experts have been working to figure out how the parasite got into food supplies since it began sickening people late last month.

Current test results point to lettuce or salad greens as the culprit, the Michigan Department of Health and Human Services announced Monday afternoon, although the agency said that "other food items cannot be completely ruled out."

No specific type of produce, grower or supplier has been identified as the source, the state health department said.

“Although we do not have a definite product identified as the source of the outbreak, we want to let Michiganders know what we have learned so far so they can take steps to protect their families,” said Natasha Bagdasarian, the state's chief medical executive, in a statement. “Early information has shown lettuce as a common product that regularly comes up during the investigation. We will continue to provide updates as we learn more.”

Prior outbreaks of cyclosporiasis in the U.S. and Canada have been linked to bagged salad, fresh cilantro, fresh basil, raspberries, snow peas and green onions, officials said.

Cyclospora is a parasite that causes frequent, watery diarrhea, as well as nausea and stomach cramps. It is contracted by eating or drinking something contaminated with the parasite.

As of Monday, more than 2,640 cases have been reported in Michigan. Typically, the state only records 40-50 cases annually. State health workers have interviewed more than 1,000 people who have contracted the parasite in an effort to find a conclusive source.

The Michigan Department of Health and Human Services is working with state and federal partners to track cases. As of July 9, 843 cases across 31 states had been reported across the country since May, according to the Centers for Disease Control and Prevention.

State officials said "given the extent of the outbreak…, it will take some time for agencies to complete their investigation."

To avoid cyclosporiasis, experts urge consumers to wash all produce and cook it rather than eating it raw whenever possible.

For lettuce and salad greens, the state health department recommends:

— The purchase of whole heads of lettuce rather than pre-washed, bagged lettuce or pre-mixed salad kits.

— The discarding of the two or three outer layers of leaves before preparation.

— Washing the inner leaves thoroughly under clean, running water.

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