Michigan is experiencing an unprecedented outbreak of cyclosporiasis, an intestinal illness caused by the microscopic parasite Cyclospora cayetanensis, with case numbers climbing rapidly to 1,251 as of 9 July and 44 people hospitalised. The outbreak matters because it dwarfs the state's typical annual totals — the July count alone is already about 25 times Michigan's usual yearly figure of around 50 cases — and investigators have yet to identify how people are becoming infected. Cases are also rising sharply across the border in Ohio, where reports indicate more than 500 infections.

The outbreak began with two cases on 22 June before rising steeply, reaching 572 by 4 July and peaking at 239 reports in a single day on 8 July. The epicentre is the south-eastern corner of Michigan, with the parasite typically spread through contaminated produce or drinking water rather than person to person. Symptoms, usually beginning about a week after infection, centre on watery and sometimes explosive diarrhoea alongside nausea, fatigue, cramping and bloating, and can persist for a month or more untreated; the illness can be treated with the antimicrobial trimethoprim-sulfamethoxazole (Bactrim). Officials advise caution with produce previously linked to outbreaks — including bagged lettuce, green onions, cilantro, basil, snow peas and raspberries — recommending thorough washing or, most safely, cooking.