• Posted July 7, 2026

Michigan, Other States See Unusual Spike In Parasite That Causes 'Explosive' Diarrhea

A parasite that causes severe, watery diarrhea is spreading across the United States, and health officials in Michigan are racing to explain an unusual surge in cases.

Michigan's outbreak has grown fast. It has recorded 572 cases of cyclosporiasis as of July 4, up from 170 on June 30, according to the state’s Department of Health and Human Services. The state typically sees about 50 cases in an entire year. 

The recent infections span seven counties in southeast Michigan, and a source has not been identified. Officials are urging anyone with symptoms to seek care.

Nationwide, at least 145 people in 17 states became sick with cyclosporiasis between May 1 and June 16, according to the U.S. Centers for Disease Control and Prevention (CDC). Those figures do not include Michigan's more recent spike or updated figures after June 16. 

At least 20 people have been hospitalized, though no deaths have been reported. Those infected range in age from 5 to 86, the CDC said.

Before June 16, New York had reported the most cases, followed by Illinois and Texas, according to NBC News’ "TODAY." The true number of infections is likely higher, because some people recover without seeing a doctor and are never tested, the CDC said.

Despite the clusters, there is no evidence of a single multistate outbreak tying all the cases together, the CDC said. The agency is working with the U.S. Food and Drug Administration (FDA) and local officials to trace the source. None of those infected reported traveling outside the country before getting sick.

Cyclosporiasis is caused by Cyclospora, a microscopic parasite spread through the fecal-oral route. This occurs when people eat food or drink water contaminated with feces. Person-to-person spread is unlikely because the parasite needs one to two weeks outside the body to become infectious, the CDC said.

In the U.S., past outbreaks have been linked to fresh produce such as basil, cilantro, raspberries and snow peas. Cases tend to climb every spring and summer, typically peaking between May and August. 

Infections have risen sharply in recent years; in 2019, the CDC identified an unusually high 4,703 cases.

Symptoms usually appear two to 14 days after exposure and can include appetite loss, stomach cramps, nausea, vomiting and a low-grade fever, in addition to the hallmark "explosive" diarrhea. Illness can last from a few days to more than a month, and symptoms may fade and return in waves.

Most healthy people recover on their own, though the infection is often treated with an antibiotic, the CDC said. People with weakened immune systems have a higher risk of prolonged illness and relapse.

More information

Visit the U.S. Centers for Disease Control and Prevention to learn more about cyclosporiasis.

SOURCES: NBC News "Today," July 3, 2026; U.S. Centers for Disease Control and Prevention, July 1, 2026; Michigan Department of Health and Human Services, July 4, 2026