Over 1,400 Hit by ‘Explosive Diarrhea’ Parasite in Michigan and Ohio — No Source Found Yet

Michigan averaged roughly 50 cyclosporiasis cases per year before this summer. By July 9, 2026, the state had confirmed 1,251. That single number tells you almost everything about how unusual this outbreak is – but it doesn’t tell you where the parasite came from, and that’s exactly what investigators are still trying to figure out.

The illness at the center of the crisis is cyclosporiasis, caused by a microscopic parasite called Cyclospora cayetanensis. Its calling card, as an intestinal illness, is diarrhea – specifically, watery diarrhea that follows after people eat food or drink water contaminated with Cyclospora, which is why the pathogen has picked up the blunt nickname “explosive diarrhea parasite” in media coverage. For the thousands of people who have been sickened across Michigan and Ohio in recent weeks, that clinical language translates to days or weeks of debilitating illness with no clear end in sight.

The outbreak escalated with remarkable speed. As of June 30, Michigan health officials had logged just over 170 cases concentrated in Monroe, Lenawee, Washtenaw, Wayne, Livingston, Shiawassee, and Jackson counties – a cluster that emerged in barely nine days, in a state that typically records around 50 cyclosporiasis cases in an entire year. Within days, that figure was doubling. By July 9, the Michigan Department of Health and Human Services confirmed 1,251 total cases, with 44 hospitalized, while the source of the outbreak remained unidentified.

How Michigan and Ohio Cases Compare

Cases of the fast-moving parasitic illness linked to contaminated produce exceeded 1,400 in Michigan and Ohio combined, putting public health officials on alert as investigators had yet to identify the source. Ohio’s trajectory, while less dramatic in raw numbers, showed just as steep an acceleration. As of July 2, the Ohio Department of Health reported at least 177 cyclosporiasis cases for 2026, of which 171 occurred since late June. Cases were confirmed across 43 counties in Ohio.

Michigan and Ohio combined reported at least 72 hospitalizations, with Michigan accounting for 44, and no deaths were logged in either state. Those hospitalization numbers reflect a real severity burden for a disease that health officials still describe, technically, as non-life-threatening for most people with healthy immune systems.

Dr. Natasha Bagdasarian, MD, MPH, FIDSA, Michigan’s chief medical executive since 2021, is board-certified in internal medicine and infectious diseases and is a Fellow of the Infectious Diseases Society of America. She said publicly that “outbreaks of cyclosporiasis have been occurring across the United States and now here in Michigan,” and based on the unusual number of cases identified in just over a week, anticipated additional cases to follow. Her working hypothesis, according to ABC News, was contaminated produce, though which product, from which supplier, and how widely it had been distributed remained unanswered questions.

What the Parasite Actually Does

The infection is caused by Cyclospora cayetanensis, a single-celled parasite that spreads through food and water contaminated with feces. In the U.S., it’s most commonly linked to fresh fruits and vegetables. When ingested, it infects the small intestine and triggers watery, uncontrollable diarrhea along with other gastrointestinal symptoms.

Beyond the diarrhea, other symptoms include cramping, bloating, low-grade fever, nausea, and vomiting. The onset isn’t immediate. People who are infected usually become sick about one week after contracting the illness, though the time between infection and sickness can span from two days to two weeks or more.

What makes cyclosporiasis particularly punishing is its duration. Without treatment, the illness can last anywhere from a few days to more than a month, and symptoms may appear to improve before returning – a pattern known as relapse. For people who assume they’re recovering and return to normal activity, that relapse can feel like being hit a second time.

One biological quirk of this parasite explains why it doesn’t spread directly between people. Cyclospora is unlikely to be transmitted directly from person to person because the parasite needs time – days to weeks – after being passed in a bowel movement to become infectious for another person. The contamination essentially has to come from a food or water source where the parasite has already had time to mature – which is why investigators are focused on the supply chain rather than contact tracing.

Why the Source Is So Hard to Pin Down

There is currently no evidence of a single multistate Cyclospora outbreak linking all cases. Rather, federal surveillance reflects a count of cases across the United States, with investigations to identify potential clusters and potential sources ongoing.

The difficulty in source identification isn’t just bureaucratic slowness. Chlorine and other common antimicrobial chemical treatments are not effective against C. cayetanensis, and as a parasite it behaves differently than other gastrointestinal pathogens that commonly cause foodborne illness. The FDA’s dedicated resource on Cyclospora and fresh produce makes clear that standard disinfection methods fail against this parasite – meaning the usual advice to wash your fruits and vegetables doesn’t reliably protect against it once contamination has occurred.

Past U.S. outbreaks have been linked to bagged salad mixes, fresh cilantro, basil, raspberries, snow peas, and scallions, which gives investigators a shortlist of suspect produce categories. In 2022, a large cluster of cases in Florida was attributed to a Caesar salad kit containing bagged romaine lettuce. That historical pattern is consistent with what local health officials are hearing now: Monroe County health department’s Lindsay Patrick told 13 ABC that investigators were asking patients about where they purchased groceries and where they ate in the two weeks before becoming ill – the incubation window that matters most.

The produce trail has also led to real-world disruptions on the consumer side. Some Taco Bell restaurants, including locations in Metro Detroit, temporarily stopped serving lettuce, guacamole, pico de gallo, and cilantro onion, posting signs citing a nationwide recall tied to the cyclospora outbreak. Taco Bell had not been identified as a source of any illnesses.

The Diagnosis Problem Most Patients Don’t Know About

If you ate something contaminated and are experiencing explosive, persistent diarrhea, getting the right diagnosis isn’t as simple as visiting a clinic. A healthcare provider can diagnose cyclosporiasis by testing a stool sample, but detecting Cyclospora can be tricky even in symptomatic patients. Standard stool testing does not typically include Cyclospora screening, and patients may need to submit multiple samples on different days, while providers must specifically request the specialized tests needed to identify the parasite.

This is a critical gap. Some patients don’t experience any symptoms, but for those who do, explosive watery diarrhea is the most common, along with cramping, bloating, low-grade fever, nausea, and vomiting. Because the symptoms resemble other illnesses, it may be hard for a patient to determine what they’re infected with.

Dr. Bagdasarian herself stated in public guidance from her office: “If you believe that you could have cyclosporiasis, it’s really important to see your healthcare provider and to mention cyclosporiasis, just in case they haven’t heard about this outbreak happening right now, and ask for stool testing, because not all stool testing routinely will include cyclosporiasis.”

The national picture underscores this. The CDC received reports of 145 cases of cyclosporiasis acquired in the United States between May 1 and June 16, 2026, and that figure explicitly excluded Michigan’s surging numbers. Among those cases, patients ranged in age from 5 to 86, with a median age of 42 and 61% female. The median illness onset date was May 13, 2026, with 20 people hospitalized and no deaths reported.

For broader context on how fresh produce routinely moves through the food safety system – and which categories turn up in recalls most often – the Hearty Soul’s coverage of the riskiest recalled foods is worth reading alongside this outbreak.

Treatment and Recovery

Cyclosporiasis is treated with the oral antibiotic trimethoprim-sulfamethoxazole, commonly sold as Bactrim, Septra, and Cotrim, taken for 10 days, according to the CDC. That combination antibiotic targets the parasite directly and significantly shortens the duration of symptoms compared to letting the illness run its course untreated.

Most patients recover fully with appropriate treatment, though immunocompromised individuals may experience prolonged illness. Those with a sulfa drug allergy should consult a healthcare provider about alternative options, as TMP-SMX is a sulfonamide (sulfa) antibiotic. Regardless of treatment, the CDC recommends rest and staying well-hydrated, particularly for those experiencing diarrhea.

Michigan health officials have also issued produce-handling guidance for restaurants, commercial kitchens, and individuals in the affected region. The state’s recommendations include buying whole heads of lettuce rather than pre-washed bagged salad or salad mixes, removing the outer two to three layers of leaves, and washing inner leaves under running water – with cooking treated as the safest option for leafy greens that can tolerate heat. Raspberries pose a specific challenge because the parasite can hide in the fruit’s bumpy surface crevices. The Michigan Department of Health and Human Services recommended frozen raspberries as an alternative, noting that freezing may reduce but does not guarantee elimination of the parasite.

What to Do Now

The parasite’s active season runs from May 1 through August 31, with the CDC monitoring cyclosporiasis occurrences in the US and helping state health departments identify and investigate outbreaks to prevent additional cases, meaning this outbreak is unfolding at the peak of the risk window. Michigan residents, particularly those in the southeastern counties hardest hit – Wayne, Monroe, Washtenaw, Livingston, Shiawassee, Jackson, and Lenawee – should treat fresh produce with extra caution right now. The key steps are buying whole heads of lettuce instead of bagged salad mixes, washing all raw produce thoroughly under running water (even though rinsing isn’t guaranteed to eliminate the parasite), and cooking produce when possible. For raspberries and other soft fruits, frozen is the safer choice until investigators identify and remove the contaminated source.

Anyone experiencing sudden, persistent watery diarrhea should contact a healthcare provider and specifically mention cyclosporiasis by name. Don’t assume a standard stool test will catch it – ask for the specific test. If a provider prescribes TMP-SMX (Bactrim or Septra), complete the full 7 to 10-day course even if symptoms improve early, because the parasite can rebound. The CDC notes that “the true number of people sick with cyclosporiasis was likely higher than the number reported,” which means many people are probably suffering through this illness without a diagnosis and without access to the treatment that would end it faster.

Disclaimer: This information is not intended to be a substitute for professional medical advice, diagnosis, or treatment and is for information only. Always seek the advice of your physician or another qualified health provider with any questions about your medical condition and/or current medication. Do not disregard professional medical advice or delay seeking advice or treatment because of something you have read here.

AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.

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