Cyclosporiasis Outbreak Hits 31 US States, CDC Reports

A widespread outbreak of cyclosporiasis, an intestinal illness caused by the microscopic parasite Cyclospora cayetanensis, has been detected across 31 U.S. states, with health officials warning that the true number of infections is likely far higher than confirmed figures suggest. As of July 9, the Centers for Disease Control and Prevention has received reports of 843 confirmed domestic cases since May 1, with 86 hospitalizations and no deaths reported, according to the CDC.

The Scope of the Outbreak

Michigan has emerged as the hardest-hit state, with the Michigan Department of Health and Human Services reporting 1,562 cases as of July 10. Cases in the state surged by more than 1,000 in a two-week period alone. New York follows closely with approximately 470 cases statewide, including at least 273 in New York City, according to CBS New York. Ohio has reported 177 cases across 43 counties, while Illinois has recorded 141 cases, which officials described as “higher-than-average.”

The CDC estimates a six-week gap between illness onset and case reporting to federal authorities, meaning the current figures likely represent only a fraction of actual infections. The agency is also aware of more than 1,500 additional cases that require further analysis to confirm as domestically acquired cyclosporiasis.

What Is Cyclosporiasis?

Cyclosporiasis is a gastrointestinal illness caused by ingesting food or water contaminated with the Cyclospora parasite. Symptoms include watery diarrhea (often explosive), loss of appetite, weight loss, stomach cramps, nausea, vomiting, muscle aches, and fatigue. The incubation period typically ranges from two days to two weeks or more, and if left untreated, the illness can last from a few days to over a month.

Importantly, the illness does not spread from person to person. As Dr. Caitlin Rivers, an epidemiologist at the Johns Hopkins Center for Health Security, explained, transmission occurs exclusively through the fecal-oral route via ingestion of contaminated food or water. The parasite requires time outside the host to become infectious, a process known as sporulation.

Investigation and Challenges

The source of the outbreak remains unidentified despite ongoing investigations by the CDC, the Food and Drug Administration, and state health departments. Investigators are interviewing patients to identify common foods consumed before illness onset, but the task is complicated by the parasite’s long incubation period.

“Contamination typically occurs at the farm or irrigation level, making traceback investigations difficult,” Rivers wrote in a July 8 newsletter, as reported by the BBC. Previous U.S. outbreaks have been linked to imported fresh produce including raspberries, basil, cilantro, snow peas, lettuce, and bagged salad mixes. In 2018, McDonald’s removed salads from more than 3,000 restaurants in 14 states after a cyclosporiasis outbreak, and in 2013, tainted lettuce imported from Mexico was suspected of sickening approximately 400 people.

Dr. Bruce Vanderhoff, director of the Ohio Department of Health, emphasized the seriousness of the illness, stating that “cyclosporiasis is a serious illness that can cause dehydration and require people to seek emergency medical care, and it should be taken seriously.”

Affected Demographics

Among confirmed cases, those sickened range in age from 5 to 88 years, with a median age of 44. Fifty-nine percent of cases are female. The median illness onset date is June 18, 2026, with cases ranging from May 1 to July 5. In addition to domestic cases, 343 travel-associated cases have been reported by 32 states involving individuals who acquired the infection outside the United States.

Prevention and Treatment

Health officials recommend several measures to reduce the risk of infection. Cooking produce to 158 degrees Fahrenheit (70 degrees Celsius) kills the parasite. While thorough washing of fresh produce is recommended, the CDC notes that the parasites are not easy to rinse off completely. Standard food safety practices, including washing hands with soap and water before and after handling fresh produce, remain important.

Michigan’s health department has specifically recommended that restaurants thoroughly wash greens, cook raspberries and leafy greens when possible, and remove outer layers of lettuce and green onions.

Anyone experiencing symptoms such as persistent watery diarrhea or dehydration is encouraged to see a healthcare provider. Cyclosporiasis is typically treated with antibiotics, most commonly trimethoprim-sulfamethoxazole.

What to Watch For

Given the six-week reporting lag, case counts are expected to continue rising through August, with the cyclosporiasis season running through August 31. The CDC has begun publishing updated surveillance data more frequently than in previous seasons. If investigators identify a specific product or supplier as the source, a food recall may follow. For now, health officials urge the public to remain vigilant about food safety and to seek medical care if symptoms develop.

This article was compiled from reports by NPR, the CDC, BBC News, and CBS New York.