‘CDC Investigates Cyclospora Outbreak: The ‘Explosive Diarrhea’ Parasite Spreading Across the US’

What Is the Cyclospora Outbreak?

The U.S. Centers for Disease Control and Prevention (CDC) is currently investigating a widespread outbreak of cyclosporiasis, an intestinal illness caused by the microscopic parasite Cyclospora cayetanensis. Often described by health officials and patients alike as causing explosive, watery diarrhea, this infection has surged across at least 18 states since May 2026, prompting urgent public health investigations.

Michigan has been hit hardest, reporting more than 1,250 cases as of July 9 — nearly 25 times the state’s typical annual average of 40–50 cases. Other states experiencing significant spikes include Ohio (177 cases), New York (394 cases), Illinois (141 cases), North Carolina (110 cases), and Colorado (90 cases), along with cases reported in Alaska, Texas, Florida, and several others.

How Cyclospora Spreads and Causes Illness

Cyclosporiasis occurs when people ingest food or water contaminated with the cyclospora parasite. The most common transmission route is through fresh produce, such as basil, cilantro, mesclun lettuce, raspberries, and snow peas, that has been contaminated with microscopic amounts of human feces.

Once swallowed, the parasites burrow into the lining of the small intestine and begin reproducing. According to infectious disease specialist Dr. Peter Chin-Hong of the University of California San Francisco School of Medicine, the parasite destroys the intestinal lining, preventing it from absorbing water and nutrients effectively. The body’s immune response triggers inflammation, and the result is a large volume of unabsorbed water rushing through the intestine — producing sudden, forceful diarrhea.

Key Facts About Transmission

• Cyclospora spreads through contaminated food and water, not person-to-person contact.
• Outbreaks typically occur between May and August, when fresh produce consumption peaks.
• The parasite is more common in tropical and subtropical regions but reaches the U.S. primarily through imported produce.
• Domestic produce has also tested positive for cyclospora in recent years, including cilantro in 2019.

Symptoms to Watch For

Symptoms typically appear 2 to 14 days after exposure and can last from a few days to several weeks if untreated. Common symptoms include:

• Watery diarrhea — often frequent and explosive in nature
• Loss of appetite and weight loss
• Stomach cramps and bloating
• Nausea (vomiting is less common)
• Low-grade fever
• Fatigue and general malaise

Symptoms may come in cycles, with bouts of diarrhea recurring after seeming to improve. Dehydration is a serious concern, particularly in severe cases, and can lead to hospitalization.

Who Is Most at Risk?

While cyclosporiasis can affect anyone, certain groups face higher risks of severe and prolonged illness:

• Young children — Their immune systems are still developing.
• Elderly individuals — Age-related immune decline increases vulnerability.
• Immunocompromised people — Including those with advanced HIV, organ transplant recipients, and cancer patients undergoing chemotherapy.
• International travelers — Especially those visiting regions where cyclospora is endemic.

Treatment Options

Most people with healthy immune systems recover from cyclosporiasis without specific medical treatment within a week or two. However, because symptoms can be severe and prolonged, medical attention is recommended.

The standard treatment is the antibiotic trimethoprim-sulfamethoxazole (Bactrim). Rest and adequate fluid intake are critical to prevent dehydration. Anyone experiencing sudden, ongoing diarrhea should contact their healthcare provider, who can diagnose cyclosporiasis through a stool sample test.

How to Protect Yourself

The cyclospora parasite is particularly hardy. Routine washing of produce under running water significantly reduces but may not fully eliminate the risk. Here’s what health authorities recommend:

• Cook produce when possible — Heating food to at least 158°F (70°C) reliably kills the parasite.
• Wash hands thoroughly — Before and after handling food.
• Rinse all produce — Wash fruits and vegetables under running water before eating, cutting, or cooking.
• Scrub firm produce — Use a clean brush on melons, cucumbers, and similar items.
• Remove damaged areas — Cut away bruised or damaged parts of fruits and vegetables.
• Stay hydrated if ill — Drink plenty of fluids and seek medical care if symptoms persist.

Frequently Asked Questions

Can cyclospora spread from person to person?

No. Unlike many other gastrointestinal infections, cyclospora does not spread directly from person to person. The parasite requires time outside the body to become infectious after being passed in stool, making direct transmission highly unlikely.

Is cyclosporiasis life-threatening?

Cyclosporiasis is rarely life-threatening, and no deaths have been reported in the current outbreak. However, severe dehydration from prolonged diarrhea can require hospitalization, particularly in vulnerable populations.

How long does cyclosporiasis last?

Symptoms can last from a few days to several weeks. Without treatment, symptoms may persist and can relapse after appearing to improve. With appropriate antibiotic treatment, recovery is typically faster.

Should I avoid eating fresh produce?

Health officials do not recommend avoiding fresh produce altogether. Instead, practice thorough washing and, when possible, cook produce to 158°F. The health benefits of fruits and vegetables far outweigh the risks when proper food safety practices are followed.

What should I do if I think I have cyclosporiasis?

Contact your healthcare provider immediately. They can order a stool test to confirm the diagnosis. Report confirmed cases to your local health department to assist with outbreak tracking. Stay hydrated and rest until symptoms resolve.

Looking Ahead

The CDC and the U.S. Food and Drug Administration (FDA) are actively working with state and local health departments to identify the sources of these infections. Investigators are analyzing multiple clusters across different states, though no single food, grower, or supplier has been identified as the common source yet.

As summer produce season continues, health officials expect more cases to emerge and urge the public to remain vigilant. With the number of infections already far exceeding typical seasonal averages, this outbreak serves as an important reminder of the critical role food safety plays in protecting public health.