People don't know what it is that they should be avoiding.
In the height of summer, when fresh produce fills tables across the American Midwest, an invisible parasite has found its way into thousands of lives. Cyclospora — microscopic, resilient, and traveling through contaminated food or water — has infected more than 1,250 people in Michigan alone, with cases rising in Ohio, New York City, and Illinois. Federal investigators are tracing the source through a mosaic of interviews and data, but the outbreak moves faster than the inquiry, and the true scale of suffering almost certainly exceeds what any official count can capture. It is a reminder that the most ordinary acts — eating a salad, sharing a meal — can carry consequences that no amount of vigilance fully anticipates.
- Michigan's cyclosporiasis cases surged 26% in a single day, reaching 1,251 by July 9 — a number that would normally represent 25 years' worth of typical annual cases for the state.
- The illness strikes hard: explosive, prolonged diarrhea lasting days to months, with symptoms that vanish and return, pushing the young and elderly toward hospitalization.
- No confirmed source has been identified, leaving people unable to know what to avoid during peak fresh-produce season — some Taco Bell franchises pulled lettuce as a precaution, but guidance remains frustratingly vague.
- Detection requires a special lab test doctors rarely order automatically, meaning thousands of infected people are almost certainly uncounted, making the official figures a severe underestimate.
- Federal agencies are coordinating, major restaurant chains are issuing reassurances, and state health departments are interviewing patients — but the outbreak continues to climb faster than answers arrive.
By early July, Michigan was recording a parasitic outbreak at a pace the state had never witnessed. On July 9 alone, 1,251 cases of cyclosporiasis were confirmed — a 26 percent jump in a single day — clustered in the southeastern part of the state in a pattern suggesting a shared source. Ohio had logged more than 360 cases, New York City 273 since May 1, and Illinois was rising too. Federal health officials still could not identify what contaminated food or water was driving the spread.
Cyclosporiasis is not a gentle illness. The parasite causes violent, watery diarrhea that can persist for months, cycling between apparent recovery and relapse. In healthy adults it is debilitating; in young children and the elderly, it can require hospitalization. Without antibiotics, the infection simply endures. Infectious disease physician Daniel Griffin described it plainly as diarrhea that simply does not get better.
Michigan normally sees around 50 cases in an entire year. The surge pointed clearly to a contaminated, widely distributed food source — historically, US outbreaks have been linked to basil, cilantro, lettuce, and raspberries. Some Taco Bell franchises stopped serving lettuce as a precaution, and health officials advised washing leafy greens thoroughly. But without knowing the actual source, the public had little concrete guidance. As pathologist Bobbi Pritt of the Mayo Clinic noted, people simply do not know what to avoid at the very moment of year when fresh produce consumption peaks.
The investigation faced a structural obstacle: detecting cyclosporiasis requires a specialized lab test that physicians rarely order as a matter of routine. Thousands of infected people were almost certainly never tested and never counted. Experts agreed the reported figures represented only the tip of the iceberg. The CDC's last major public update had come weeks earlier, and major restaurant chains offered reassurances while Chipotle and Chick-fil-A did not respond to inquiries.
For now, guidance remained broad and incomplete — handle produce carefully, stay hydrated, seek care if symptoms persist. The parasite, indifferent to caution, continued moving through the summer food supply. The cases continued to climb.
By early July, something was moving through Michigan that public health officials could not yet name. A parasite called cyclospora was infecting people at a rate the state had never seen before. On July 9 alone, Michigan recorded 1,251 cases of cyclosporiasis—a jump of 26 percent from the day before. The infections clustered in the southeastern part of the state, a pattern that suggested a single source, a common meal, a shared supply. Neighboring Ohio had already logged more than 360 cases. New York City, since May 1, had counted 273. Illinois was rising too. The outbreak had begun its visible climb around June 22, and now, nearly three weeks later, federal health officials still did not know what people had eaten or touched that had made them sick.
Cyclosporiasis announces itself violently. The parasite, microscopic and invisible, causes watery diarrhea that can last for days or stretch into months. It arrives with nausea, stomach cramps, loss of appetite, weight loss. In healthy people it is brutal. In young children and the elderly, it can demand hospitalization. The symptoms can vanish and return without warning, a cycle of relief and relapse that wears people down. Without antibiotics, the illness persists. With them, recovery is possible but not guaranteed. Daniel Griffin, an infectious disease physician and president of Parasites Without Borders, put it plainly: "It could really be this explosive, significant diarrhea that doesn't get better."
Michigan typically sees about 50 cases of cyclosporiasis in an entire year. The surge since late June pointed unmistakably to a common source—something contaminated, something widely distributed, something people were eating now. The parasite travels through food or water that has been exposed to feces. In the United States, outbreaks have historically been traced to basil, cilantro, lettuce, and raspberries, or to infections people acquired while traveling abroad. As a precaution, some Taco Bell franchises in Michigan stopped serving lettuce. The state health department issued guidance on handling leafy greens: wash them thoroughly, cook them when possible. But without knowing the actual source, people were flying blind. "People don't know what it is that they should be avoiding," said Bobbi Pritt, a pathologist at the Mayo Clinic. "This is the time of year when we are eating a lot of fresh produce."
The investigation moved methodically. When someone tested positive—and here was the first problem—the local health department would interview them. They asked about symptoms, about restaurants visited, about grocery stores, about specific dates and items purchased. The information flowed upward to state and federal experts, building a mosaic of exposure. But the mosaic was incomplete. To detect cyclosporiasis, a doctor must order a special laboratory test. It is not routine. It is not automatic. Thousands of people with the parasite were likely never tested, never counted, never reported. "I think it's very safe to say that with all outbreaks, the numbers that are reported for any specific disease is always the tip of the iceberg," Pritt said. When you hear over 1,000 cases, Griffin added, you are probably looking at far more people out there simply not being diagnosed.
The CDC had last updated the public on June 16, when it reported 145 cases across 17 states. On July 1, the agency said there was no evidence of a single multistate outbreak. Physicians read those statements and shook their heads. The numbers were a gross undercount. The agency was working with the FDA to find the source and contain the spread, but the outbreak was moving faster than the investigation. Major restaurant chains issued statements: Wendy's said it saw no impact to its supply chain. Restaurant Brands International, which owns Burger King and Popeyes, reported no problems. Inspire Brands, parent of Dunkin' and Jimmy John's, said the same. Chipotle and Chick-fil-A did not respond. A Taco Bell spokesperson declined to comment on the lettuce precaution. The outbreak remained a mystery, and people remained sick.
For now, the guidance was simple and incomplete: avoid food and water that could be contaminated. Handle produce carefully. If gastrointestinal symptoms persist beyond a few days, seek medical care. Stay hydrated. The parasite does not care about caution. It moves through the food supply, through the summer season when fresh produce flows into kitchens and restaurants across the Midwest, waiting to be discovered or waiting to spread further. The investigation continues. The cases continue to climb.
Notable Quotes
It could really be this explosive, significant diarrhea that doesn't get better.— Daniel Griffin, infectious disease physician and president of Parasites Without Borders
The numbers that are reported for any specific disease is always the tip of the iceberg.— Bobbi Pritt, pathologist and clinical microbiologist at the Mayo Clinic
The Hearth Conversation Another angle on the story
Why is this outbreak so hard to trace? Surely with modern food supply tracking we should know where it came from by now.
The parasite is microscopic and the contamination happens at some point in the chain—farm, processing, distribution, restaurant kitchen. You're looking for a needle in a haystack made of lettuce. And you only find cases when someone gets sick enough to see a doctor and that doctor thinks to order the right test.
So the real number of infected people could be much higher than 1,251?
Much higher. Experts are saying what we're seeing is the tip of the iceberg. Some people have mild symptoms and never go to a doctor. Some go to a doctor who doesn't test for this specific parasite. The outbreak is bigger than the numbers suggest.
What makes this parasite so dangerous compared to other foodborne illnesses?
It doesn't just hit and leave. It can last for months. Symptoms come and go. You think you're better and then it flares up again. For elderly people and young children, that kind of prolonged illness can mean hospitalization. For anyone, it's exhausting.
Why are restaurants being so cautious about lettuce if they don't know that's the source?
Because lettuce is a known vector for this parasite in past outbreaks. It's a reasonable precaution when you don't have answers. But it's also a guess. The real source could be something else entirely—basil, cilantro, raspberries, something imported. Until investigators know, everyone is working in the dark.
What happens next?
The CDC and FDA keep investigating. People keep getting sick. Doctors keep testing. Eventually the pattern will emerge—enough cases will cluster around a specific product or supplier that the source becomes clear. But by then, how many more people will have been infected?