US Cyclosporiasis Outbreak: What to Know About the Parasite Causing Explosive Diarrhea

A growing outbreak of cyclosporiasis has raised public health concerns across the United States. More than 3,000 people in 31 states have been infected, prompting health officials to issue precautionary advice while investigators continue searching for the source of the outbreak.

Although cyclosporiasis is common during the summer in the U.S., officials have not yet identified the exact source of the parasite.

Historically, Cyclospora outbreaks have been linked to imported fresh produce such as raspberries, basil, cilantro, snow peas and mixed salad greens. Officials fear that additional infections could continue during the peak season.

What is cyclosporiasis?

Cyclosporiasis is a foodborne and waterborne intestinal infection caused by the parasite Cyclospora cayetanensis. People become infected after consuming food or drinking water contaminated with the parasite. Fresh produce—including leafy greens, herbs, salad vegetables, and berries—has been linked to previous outbreaks because people often eat these foods raw.

Unlike bacteria such as Salmonella or E. coli, Cyclospora is a parasite that requires specialised laboratory methods for its detection.

Symptoms and incubation period

The most common symptom is frequent watery diarrhoea, which is sometimes described as “explosive diarrhoea.” Other symptoms include stomach cramps, nausea, loss of appetite, fatigue, weight loss, and occasionally a low-grade fever.

Symptoms usually appear one to two weeks after infection, which is much longer than many other foodborne illnesses. As the long incubation period makes it difficult for patients to remember exactly what they ate before becoming ill, officials still do not know which food or water source is responsible.

Government response and differing expert opinions

The US Department of Health and Human Services (HHS) confirmed that the CDC is monitoring Cyclospora through other surveillance systems and is maintaining funding for foodborne disease programmes.

How people can protect themselves

Health officials recommend several preventive measures:

• Wash fruits and vegetables thoroughly before eating.
• Cook vegetables when possible, as heat can kill the parasite.
• Be cautious with fresh produce that has previously been associated with Cyclospora outbreaks, including raspberries and leafy greens.
• Practise good food hygiene and follow updates from local health authorities.
• Seek medical care if severe or prolonged diarrhoea develops, as cyclosporiasis can be treated with antibiotics.