Cyclospora outbreak causes severe diarrhea across several states

Michigan’s cyclospora outbreak climbed to 992 reports by July 8, up from 572 just four days earlier, as health officials tracked a parasitic illness that has now reached multiple states and sent patients to the hospital. The Centers for Disease Control and Prevention had counted 145 U.S.-acquired cases across 17 states as of June 16, with 20 hospitalizations and no deaths, a reminder that this severe diarrhea outbreak is spreading faster than investigators can pin down its source.

Cyclosporiasis is an intestinal illness caused by the microscopic parasite Cyclospora cayetanensis. It spreads when people ingest food or water contaminated with stool, and the CDC says it is usually not life-threatening. The symptoms can be punishing: watery diarrhea, loss of appetite, weight loss, cramping, bloating, nausea, fatigue, vomiting, body aches, headache and low-grade fever. Without treatment, the illness can last from a few days to a month or longer and may relapse. Trimethoprim-sulfamethoxazole, or TMP-SMX, is the treatment of choice, and there is no vaccine.

Produce has been the recurring weak point in past U.S. outbreaks. Investigators have linked earlier cases to raspberries, basil, cilantro, snow peas, mesclun lettuce and other fresh produce, which can move through a fragmented supply chain before anyone realizes contamination has occurred. In Michigan, state officials said as of July 4 they had not identified a specific produce grower, supplier or produce type as the source. The outbreak has reached counties across Southeast Michigan, including Monroe, Lenawee, Washtenaw, Wayne, Shiawassee, Jackson, Oakland and Livingston.

The investigation has also been slowed by Cyclospora’s timing. The CDC says cases are often scattered, and interviews commonly happen four to six weeks after illness begins, long after a sick person may have eaten the contaminated item. The FDA says infected people can shed the parasite in feces, allowing it to contaminate food, water and the environment, which adds another layer of risk when a source remains unknown.

Cyclosporiasis is monitored year-round in the United States, but the main season runs from May 1 through August 31, and the 2026 season began on May 1. Maryland has reported 32 cases this year, 28 of them since May 1, and Virginia reported 10 cases in its July 7 update. The outbreak now sits at the intersection of patient care, produce tracing and supply-chain oversight, with public health agencies still working to identify where the parasite entered the food system.