Michigan Cyclosporiasis Outbreak: Lettuce or Salad Greens Identified as Potential Source

Michigan health officials said on July 13, 2026, that lettuce or salad greens are a potential source of a cyclosporiasis outbreak that has reached 2,640 cases and 44 hospitalizations in the state, roughly 50 times the annual caseload Michigan would expect in a normal year. The Michigan Department of Health and Human Services said no specific type of produce, grower, supplier, or distributor had been identified, and that other food items had not been ruled out.

What Michigan Investigators Found

The department's July 13 press release stated that more than 1,000 interviews with people who tested positive for the parasite had been completed by the time investigators went public with their findings. Those interviews pointed toward lettuce and salad greens.

"Early information has shown lettuce as a common product that regularly comes up during the investigation," Dr. Natasha Bagdasarian, Michigan's chief medical executive, said in the July 13 statement. She added that the source remained unconfirmed and that other foods had not been eliminated.

Michigan ordinarily records 40 to 50 cyclosporiasis cases per year. The state counted 170 cases on June 30, 572 by July 4, and 2,640 by the morning of July 13, a jump of more than 1,000 cases over a single weekend. Two factors are complicating the pace of the investigation Cyclospora cayetanensis has an incubation period of up to two weeks, and modern food distribution sends a single lot of produce through multiple processors, warehouses, retailers, and food service operators before reaching the end consumer.

"Produce may have been grown on the other side of the country, possibly even in other countries, then processed somewhere else before coming into Michigan," Bagdasarian said, explaining why the traceback work is expected to take considerable time.

The National Picture

The outbreak is not confined to Michigan. CDC surveillance data recorded 843 domestically acquired cyclosporiasis cases across 31 states as of July 9, 2026, with 86 hospitalizations and no deaths. State health departments are reporting higher cumulative totals, the CDC's confirmed tally reflects only cases that have cleared the national case definition and the review process, a lag the agency estimates at roughly six weeks from illness onset to federal confirmation. Multiple states reported case increases over the two weeks ending July 9, compared with the same period in 2025, according to the CDC's July 10 update.

The FDA's active outbreak investigation table lists several Cyclospora investigations opened in June and July 2026 with food sources not yet identified. Those entries reflect national traceback work and have not been publicly linked to the Michigan lettuce signal. No FDA product recall or public advisory naming a specific brand, grower, or supplier had been issued as of July 14, 2026.

Ohio has also reported a substantial rise in cases, with 364 cases counted by July 10 according to state health officials. Earlier coverage from this publication tracked the Michigan outbreak when the state total was below 300, the figure has multiplied more than eightfold since then.

Why Cyclospora Is Difficult to Diagnose and Trace

Cyclospora cayetanensis is a microscopic parasite, not a bacterium. That matters for both diagnosis and traceback. The genomic fingerprinting methods that can rapidly connect Salmonella or E. coli strains across state lines are not yet as reliable for Cyclospora, a limitation that prolongs the process of linking patients to a common food source.

Testing in patients is equally demanding. According to the CDC, Cyclospora is not included in standard laboratory stool panels, so a clinician must specifically request it. Because the parasite sheds in stool intermittently, a single negative result does not rule out infection, and several specimens collected on different days may be necessary to confirm a case.

Once confirmed, CDC clinical guidance recommends a seven-to-ten-day course of trimethoprim-sulfamethoxazole, available under the brand names Bactrim and Septra, as the standard treatment for adults. Without it, the illness can persist for weeks, and symptoms typically relapse after appearing to clear.

Person-to-person transmission is considered unlikely. The parasite requires at least one to two weeks outside the human body before it can infect a new host. MDHHS also reported no evidence linking recreational water use to the 2026 Michigan outbreak, which distinguishes this investigation from some historical Cyclospora cases tied to swimming pools and contaminated irrigation water.

Prior U.S. Outbreaks Have Repeatedly Involved Fresh Produce

Cyclospora has moved through U.S. food supply chains before. A 2018 outbreak linked to Fresh Express salad mixes served at McDonald's restaurants resulted in 511 confirmed illnesses in 15 states and New York City, according to the FDA and CDC. A separate 2020 cluster was tied to Fresh Express bagged salads containing iceberg lettuce, red cabbage, and carrots, which reached 690 confirmed cases across 13 states. A 2019 investigation traced another multi-state cluster to fresh basil imported from Mexico. The parasite has also been associated with cilantro, snow peas, raspberries, and green onions in earlier investigations in the United States and Canada.

None of those historical food items has been identified in connection with the 2026 cases. No specific product from any grower, processor, or brand has been publicly named in the current investigation.

Handling Advice from Health Officials

MDHHS issued specific handling guidance for lettuce and salad greens while the investigation continues. Shoppers and commercial kitchens are advised to buy whole heads of lettuce rather than pre-washed bagged varieties or pre-made salad kits. The outer two to three leaves should be discarded. Inner leaves should then be washed under clean running water. The department noted that a "pre-washed" label does not guarantee safety and that rewashing bagged lettuce is unlikely to remove the parasite from contaminated product.

Heating food to 158°F (70°C) or higher is the only method confirmed to kill Cyclospora, according to the July 13 MDHHS guidance. Washing alone does not reliably dislodge the parasite. Freezing does not kill it. MDHHS recommends cooking leafy greens wherever possible rather than serving them raw.

Anyone experiencing frequent watery diarrhea, the outbreak's most common symptom, along with stomach cramps, nausea, bloating, or fatigue should contact a healthcare provider and specifically request Cyclospora testing. Higher-risk groups, including older adults, young children, organ transplant recipients, and people undergoing chemotherapy, should take particular care with fresh produce during the investigation period, according to MDHHS.

What Comes Next

The CDC and FDA are conducting parallel national investigations. MDHHS updates its Michigan case count daily, Monday through Friday, by 11 a.m. Eastern Time, hospitalization data are refreshed weekly on Thursdays.

The investigation's timeline depends on how quickly traceback work can connect a common ingredient across affected households and food service operations. Given the length of the parasite's incubation period and the complexity of the distribution chain, MDHHS said it anticipates the process will take some time. The cyclosporiasis season typically runs through August 31, leaving seven weeks of elevated transmission risk from the time of writing.