What is cyclosporiasis and why is Michigan's outbreak quadrupling?

What cyclosporiasis is and why the parasite keeps appearing in summer

Cyclosporiasis is a diarrheal illness caused by Cyclospora cayetanensis, a microscopic parasite that — unlike many foodborne bugs — does not spread from person to person. According to the Centers for Disease Control and Prevention, almost every outbreak in the United States has been traced to contaminated fresh produce. The agency tracks a predictable seasonal window: most U.S. cases appear between May 1 and August 31, the months when domestic berries, herbs and salad greens dominate consumer plates and restaurant menus. Past multistate outbreaks named by the CDC and the Michigan Department of Health and Human Services have involved bagged salad mixes, fresh cilantro, fresh basil, raspberries, snow peas and scallions — a list worth remembering because it reflects how often the parasite finds a foothold in items that are eaten raw and are hard to disinfect.

The parasite is unusually stubborn on the surface of food. Dr. Brian Kaminski of ProMedica Health System told NBC News that Cyclospora “clings to produce,” which is why rinsing under running water reduces risk but does not eliminate it. Raspberries in particular are difficult to clean because their tiny hairs give the parasite something to grip. Symptoms typically develop one to two weeks after a person eats the contaminated item, a lag that turns every new case into a detective story about meals eaten days earlier.

Michigan’s outbreak, in numbers

The Michigan Department of Health and Human Services said on July 7, 2026 that it had received more than 700 reports of cyclosporiasis since June 22, with 38 patients needing hospital treatment, CBS Detroit reported. The growth has been unusually steep:

• June 30: 170 confirmed cases in Michigan.
• July 3: 400 cases.
• July 4: 572 cases.
• July 6: 680 cases.
• By July 7: more than 700 reports statewide.

Most cases are concentrated in southeast Michigan, with Monroe County at the center and additional reports from Jackson, Lenawee, Livingston, Oakland, Shiawassee, Washtenaw and Wayne counties. ProMedica Health System, which operates across southeast Michigan and northwest Ohio, told NBC News it had logged 411 cases as of the Monday before publication, and Dr. Matthew Sims of CoreWell Health in Royal Oak said Ohio, North Carolina, Illinois and New Jersey are also reporting illnesses. No deaths have been reported.

Why this is so unusual for Michigan

The state’s chief medical executive, Dr. Natasha Bagdasarian, called the trajectory “highly unusual,” noting that Michigan usually sees 40 to 50 cases a year, NBC News reported. That makes the current count roughly 14 times the typical annual caseload, compressed into about 10 days. Dr. Anurag Malani, vice chief of staff at Trinity Health Ann Arbor, told NBC News it is “easy” for Michigan to reach 1,000 cases.

The outbreak was first made public in late June when the Monroe County Health Department said it was investigating a cluster. State health officials have since widened their requests to patients, asking not only what restaurants they visited and what they ordered, but also where they grocery shop and which specific items they bought. Dr. Kaminski told NBC News that staff are “pulling people’s grocery shopping lists” and working overtime.

What officials say — and don’t say — about the source

The cause of the surge has not been determined. The Food and Drug Administration told NBC News that an investigation is ongoing and added: “We are not in a position at this time to characterize the current numbers as definitively unusual pending the completion of that investigation.” A CDC spokesperson was more categorical, telling NBC News the agency “has no evidence of a single, multistate Cyclospora outbreak linking cases happening right now and being reported in the press.” That language leaves room for several competing interpretations: a single contaminated product distributed nationwide, several separate regional outbreaks happening simultaneously, or a baseline seasonal rise that is being amplified by heightened testing and awareness.

The Michigan Department of Health and Human Services has not named a supplier, grower or commodity. Until it does, the outbreak remains a confirmed spike without a confirmed vector.

Why it matters: strained labs, hospital capacity and an underreported national picture

The most concrete second-order effect is on clinical laboratories. Kaminski told NBC News that test turnaround times have stretched from about 24 hours to two to three days, and warned that if delays persist, doctors may have to start treating patients on symptoms alone rather than waiting for confirmatory results. That is a meaningful shift: cyclosporiasis is treated with an antibiotic (usually Bactrim), but empirical antibiotic use carries its own costs in side effects and resistance pressure.

A second consequence is regional. ProMedica alone accounts for 411 cases across southeast Michigan and northwest Ohio, and Kaminski described the cross-border pattern as an “epidemic cluster” — language that implies health systems, not just health departments, are now coordinating a response. Thirty-eight hospitalizations so far signal that even in a generally self-limiting illness, the cumulative burden on emergency departments and inpatient beds during peak summer can be non-trivial.

A third concern is surveillance. NBC News noted that as of July 2025 the CDC made tracking cyclospora optional as part of scaling back its Foodborne Diseases Active Surveillance Network (FoodNet). Food-safety experts warned at the time that the change could make it harder to identify and respond to outbreaks. The CDC’s most recent national tally — 145 cases across 17 states from the start of May through June 16 — is “likely a vast undercount,” the agency told NBC News, which means the true geographic spread of the current surge is still uncertain.

Comparisons that put the numbers in perspective

Michigan’s roughly 700 cases in 10 days versus an annual baseline of about 50 is the cleanest comparison, but it is worth layering it against typical U.S. cyclosporiasis seasons. The CDC has historically reported several hundred to a few thousand domestically acquired U.S. cases each year, usually clustered in late spring and summer. A single state approaching or exceeding 1,000 cases in a matter of weeks would be at the upper end of anything recorded in recent years, which is why Malani’s 1,000-case projection drew attention.

Hospitally, 38 admissions against more than 700 cases is a roughly 5% hospitalization rate — higher than would be expected for a routine norovirus season but consistent with outbreaks that include older adults and people with underlying conditions, who are most prone to severe dehydration.

What to watch next

Three specific signals will determine whether this outbreak plateaus or escalates. First, whether the FDA names a specific commodity, supplier or grower and whether it issues a recall or public advisory; absent that, the investigation is still in the hypothesis-generating phase. Second, whether Michigan’s case count crosses the 1,000-case threshold Malani flagged and whether lab turnaround times force clinicians into empirical antibiotic treatment. Third, whether the CDC’s optional-surveillance stance delays the national picture: if other states are experiencing similar upticks but not reporting them through formal channels, the official case curve will lag the real one.

In the meantime, Michigan health officials are urging restaurants and commercial kitchens in southeast Michigan to wash produce under clean running water, cook it where possible, and use extra caution with bagged salad mixes, fresh herbs and berries — the same categories that have anchored past outbreaks and that, for now, are the only practical leads public-health teams have.