A nasty gastrointestinal bug is rapidly spreading in several states, with more than 700 cases confirmed in Michigan over the last few weeks. The demand for tests for cyclosporiasis, a pathogen often caused by contaminated fresh produce, is so intense, with so many patients seeking help for diarrhea and crippling abdominal cramps, that many labs can’t keep up. Subscribe to read this story ad-freeGet unlimited access to ad-free articles and exclusive content.The source of the fast-moving illnesses is unknown, although the Food and Drug Administration said an investigation is ongoing. Cases in Michigan could easily reach 1,000, said Dr. Anurag Malani, vice chief of staff at Trinity Health Ann Arbor. “There are many more cases that are yet to come.”Meanwhile, health officials are scrambling to figure out what people are eating that’s making them sick.“We’re pulling people’s grocery shopping lists,” said Dr. Natasha Bagdasarian, chief medical executive for the state of Michigan. Staff, she said, are working overtime as cases have increased precipitously in recent weeks: 708 cases over the course of about 10 days. It’s “highly unusual,” Bagdasarian said, as the state usually sees 40 to 50 cases a year. Cyclosporiasis cases tend to increase during the summer, usually between May 1 and Aug. 31, according to the Centers for Disease Control and Prevention. Most cases are centered in the southeastern part of Michigan, although illnesses have also been reported in Ohio, North Carolina, Illinois and New Jersey, among others. The FDA and CDC are monitoring the outbreaks, an FDA spokesperson said in an email. “We are not in a position at this time to characterize the current numbers as definitively unusual pending the completion of that investigation,” the spokesperson said.The disease — cyclosporiasis — is a foodborne illness caused by a microscopic parasite called cyclospora. Fresh produce is almost always the source. Previous outbreaks have involved raspberries, bagged lettuce or salads, cilantro, and basil. Symptoms include explosive, watery diarrhea. People may also have unusually bad gas, stomach cramps, nausea and loss of appetite.According to the CDC, 145 cases of cyclosporiasis in 17 states were reported from the beginning of May through June 16, although those numbers are likely a vast undercount. “CDC has no evidence of a single, multistate Cyclospora outbreak linking cases happening right now and being reported in the press,” a CDC spokesperson wrote in an email. However, as of July 2025, the CDC made tracking cyclospora optional, as part of scaling back its Foodborne Diseases Active Surveillance Network. At the time, food safety experts worried that it could make it harder to identify and respond to outbreaks. Dr. Brian Kaminski, vice president of medical affairs at ProMedica Health System, which cares for patients in both southeast Michigan and northwest Ohio, said cases in the two states appear to be part of an “epidemic cluster.”“When we started seeing cases of persistent diarrhea showing up, we knew there’s something going on,” Kaminski said. “I would say that trend continues.” As of Monday, the ProMedica Health System accounted for 411 cases. Cyclosporiasis does not spread from person to person, unlike norovirus, a highly contagious stomach bug that usually runs its course in a few days. Left untreated, cyclosporiasis can linger for weeks. It’s treated with an antibiotic, usually Bactrim. Some people have needed to be hospitalized, often from dehydration, Malani said. No deaths have been reported.“The question is, where is it coming from, and are all the states connected, or are there multiple outbreaks happening?” said Dr. Matthew Sims, director of infectious diseases research at Corewell Health in Royal Oak, Michigan.It can take one to two weeks for symptoms to develop after eating contaminated food, which can complicate the investigation. Bagdasarian said that health officials are asking each patient what restaurants they’ve been to in the past couple of weeks, what they ordered, where they grocery shop and what items they purchased.Testing in some areas has become strained. “Turnaround time was initially about 24 hours, and we’re two to three days out now,” Kaminski said. If those delays continue, it’s possible that doctors may need to start treating people based on symptoms alone, rather than waiting for confirmatory results. How to stay safe from cyclosporaRinsing produce can reduce the risk for cyclosporiasis but doesn’t eliminate it. The parasite, cyclospora, “clings to produce,” Kaminski said. Michigan health officials are encouraging people to buy whole heads of lettuce and remove outer leaves where there could be contamination before washing it. Raspberries in particular can be difficult to clean because they’re covered in tiny hairs that the parasite likes to hang on. It’s possible that freezing can kill the parasite, Sims said, but it’s not guaranteed. Cooking food is the only sure way to kill it.