Parasite that causes ‘explosive diarrhea’ spreads to 17 US states

Parasite that causes ‘explosive diarrhea’ spreads to 17 US states

Federal health officials are investigating a surge of parasitic infections across 17 U.S. States that cause severe gastrointestinal distress. The illness, known as cyclosporiasis, has sickened hundreds of people since May 1, 2026, according to the U.S. Centers for Disease Control and Prevention (CDC).

The infection is caused by Cyclospora cayetanensis, a microscopic parasite found in human feces. It spreads via the fecal-oral route, typically when people consume food or water contaminated with the parasite. While the illness is most common in tropical and subtropical regions, the U.S. Typically sees a seasonal spike between May 1 and August 31.

Between May 1 and June 16, the CDC tracked 145 confirmed cases across 17 states, including Alaska, Colorado, Connecticut, Florida, Georgia, Louisiana, Massachusetts, New Jersey, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, and Wisconsin. New York reported the highest number of cases, with between 31 and 80. Texas and Illinois followed, each reporting between 11 and 30 cases.

The infected individuals range in age from 5 to 86, with a median age of 42. Women make up 61% of reported cases. While no deaths have been reported, 20 people have been hospitalized.

Michigan Cluster

While the CDC manages the national surveillance, Michigan is facing a separate, "sudden and large" increase in cases. Since June 22, 2026, more than 170 cases have been reported across seven counties: Jackson, Livingston, Lenawee, Monroe, Shiawassee, Washtenaw, and Wayne.

This spike is significantly higher than the state's typical annual total of around 50 cases. State health officials have not yet determined if the Michigan cluster is connected to the broader national investigation or is linked to a different food source.

Symptoms and Treatment

The hallmark of cyclosporiasis is watery, often explosive diarrhea that can last for several weeks or even months if left untreated. Other symptoms include:

• Nausea and vomiting
• Stomach cramps and bloating
• Loss of appetite and weight loss
• Fever and muscle pain
• Fatigue

Symptoms usually appear about a week after exposure, but can emerge as early as two days or as late as two weeks. The CDC notes that symptoms can occur in waves, leading to relapses.

Most healthy people recover on their own, though recovery can take several weeks. For those requiring treatment, an anti-parasitic drug called trimethoprim-sulfamethoxazole is effective for most patients. People with weak immune systems are at a higher risk for prolonged illness.

Identifying the Source

The CDC, the U.S. Food and Drug Administration (FDA), and state health departments are working to find the source. While the parasite is often linked to fresh produce, investigators have not yet pinpointed a specific cause for the current cases. In a July 1 update, the CDC stated there is no evidence of a single, multi-state cyclospora outbreak linking all cases.

Past outbreaks in the U.S. Have been tied to raw produce, including:

• Basil, cilantro, and snow peas
• Raspberries
• Leafy greens and bagged salad mixes
• Pre-packaged vegetable trays

In 2018, 761 confirmed illnesses were linked to produce, including restaurant salads from McDonalds. In 2022, a Florida cluster was attributed to a Caesar salad kit with bagged romaine lettuce.

Prevention and Limitations

The parasite cannot spread directly from person to person. Because Cyclospora is microscopic and can hide in crevices, the CDC warns that washing produce may reduce risk but is not a guarantee of removal. Cooking is the only reliable way to kill the parasite.

Experts note that the reported number of cases is likely lower than the actual number of infections. According to Dr. Bobbi Pritt, Chair of the Division of Clinical Microbiology at the Mayo Clinic, the parasite is not detected by simple stool tests and requires a specific stain not typically used in standard testing.

The CDC continues to encourage healthcare providers to consider cyclosporiasis for patients with persistent diarrhea and urges the public to seek medical attention if symptoms develop after eating fresh produce.