Federal health authorities are racing to identify the source of a microscopic parasite that has infected more than a thousand people in Michigan and hundreds more across multiple states.

The surge marks one of the largest outbreaks of its kind in recent U.S. history.

According to the Associated Press, Michigan has logged over 1,200 confirmed cases of cyclosporiasis, setting a new statewide record. Ohio has reported more than 500 cases, including over 300 in Lucas County.

The Centers for Disease Control and Prevention, the Food and Drug Administration, and state agencies are jointly investigating but have not yet determined the origin of the infections. Officials say illnesses have been climbing since mid-June.

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The infection, caused by the parasite Cyclospora, leads to prolonged gastrointestinal distress. The CDC describes the hallmark symptom as watery, often “explosive” diarrhea that can last for weeks or months without treatment.

Other reported symptoms include nausea, fatigue, bloating, abdominal cramping, and significant weight loss. Though the illness can clear spontaneously, many patients require antibiotics to recover.

Michigan officials first disclosed the outbreak after confirming more than 170 new cases since June 22, concentrated in the southeastern region of the state. In a typical year, Michigan records around 50 total cases.

The parasite spreads most often during the warmer months. Federal health guidance defines the official outbreak season as lasting from May 1 through August 31, a period when infections historically increase.

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Health officials emphasize that no deaths have been reported in the current outbreak, though at least 40 hospitalizations have occurred in Michigan. Texas has also confirmed at least 48 cases this season, while infections have been documented in 28 additional states.

Past outbreaks have been tied to contaminated produce or water. The Associated Press reported that investigators are examining whether fresh fruits or vegetables may have played a role in the current wave.

Authorities continue to advise consumers to wash produce carefully before eating, even though cleaning may not completely remove contamination. Cooking vegetables can also reduce potential exposure, officials say.

Michigan state agencies recommend choosing whole heads of lettuce or prepackaged salad mixes that can be washed thoroughly at home. They further suggest discarding a few outer leaves before cleaning the remaining lettuce.

For those already experiencing suspicious symptoms, the CDC urges seeking medical evaluation and testing for cyclosporiasis to receive timely care and prevent dehydration or complications.

The federal investigation remains ongoing with multiple multistate clusters under review. As the summer continues, health experts expect additional cases to emerge until the source is definitively traced.