Cyclosporiasis, a parasitic illness causing explosive, watery diarrhea, has surged across the United States, with Michigan reporting nearly 1,000 cases in its largest outbreak ever. Ohio has also seen a sharp increase, with 177 cases as of July 2, according to state health officials. The US Centers for Disease Control and Prevention (CDC) has recorded 145 cases across 17 states as of June 16, but this data lags behind state reporting and likely undercounts the true number.
What Is Cyclosporiasis?
Cyclosporiasis is a gastrointestinal illness caused by the parasite Cyclospora cayetanensis, which spreads through raw produce and water contaminated with human feces. In the US, it is seasonal, with outbreaks typically occurring between May and August. Past outbreaks have been linked to contaminated raw fruits, vegetables, and herbs such as basil, cilantro, berries, and spinach.
The most common symptom is watery diarrhea with frequent and sometimes explosive bowel movements, according to the CDC. Other symptoms include cramps, nausea, fatigue, loss of appetite, low-grade fever, and vomiting. Symptoms can last from several days to over a month. Some infected individuals show no symptoms. The average time from ingestion to symptoms is about a week but can range from two days to two weeks. Cyclosporiasis is not usually transmitted from person to person.
Severity and Treatment
Although rarely life-threatening, cyclosporiasis can have severe effects. Most people recover without treatment, but those with weakened immune systems are at higher risk. The illness is typically treated with antibiotics. No deaths have been linked to the current outbreak, and the source of infections has not yet been identified.
Comparison to Previous US Outbreaks
Previous US outbreaks have been linked to feces-contaminated irrigation water. In 2022, a surge in Florida was caused by contaminated lettuce in packaged salad kits, sickening hundreds. Comprehensive data on cyclospora outbreaks is limited, but only a handful of documented outbreaks in the last 20 years have surpassed 1,000 cases. Notable examples include a 1996 outbreak tied to Guatemalan raspberries that sickened almost 1,500 people, and a 2019 outbreak linked to Mexican basil that sickened over 2,400 across the US and Canada.
How to Protect Yourself
To prevent infection, avoid potentially contaminated food or water. Wash fresh produce thoroughly before eating, though washing may not eliminate all risk. Fruits, herbs, and vegetables with nooks and crannies—such as raspberries, blackberries, lettuce, spinach, cilantro, green onions, and basil—are more likely to harbor the parasite. Health officials recommend purchasing whole heads of lettuce instead of pre-washed bagged mixes, removing the outer two to three leaves, and washing the remaining under running water. Cooking produce can kill the pathogen.
