Health officials across the United States are investigating a growing outbreak of cyclosporiasis, a parasitic illness that can cause severe, prolonged diarrhea and other gastrointestinal symptoms. While the source of the infections remains unknown, cases have risen sharply across several states, with Michigan reporting the largest number of infections.

The outbreak has prompted investigations by state health departments, the U.S. Centers for Disease Control and Prevention (CDC), and the Food and Drug Administration (FDA). Although no single contaminated food has been identified, experts say fresh produce remains a leading suspect based on previous outbreaks.

What is cyclosporiasis?

Cyclosporiasis is an intestinal illness caused by the microscopic parasite Cyclospora cayetanensis.

People become infected by consuming food or water contaminated with the parasite. Unlike many common stomach bugs, Cyclospora is not typically spread directly from person to person because the parasite requires time in the environment before it becomes infectious.

According to the CDC, untreated infections can last from several days to more than a month, with symptoms often disappearing and returning over time.

Where is the outbreak spreading?

Michigan has emerged as the center of the current outbreak.

According to state health officials:

• Michigan has reported 1,251 confirmed cases.
• Cases increased by approximately 26% in a single day.
• Most infections are concentrated in southeastern Michigan.

Other affected areas include:

• Ohio (more than 360 reported cases)
• New York City (273 reported cases since May 1)
• Illinois (rising infections under investigation)

Health officials believe the actual number of infections is likely much higher because specialized laboratory testing is required to diagnose the parasite.

What are the symptoms of Cyclospora infection?

The illness primarily affects the digestive system.

Common symptoms include:

• Frequent watery diarrhea
• Severe or “explosive” diarrhea
• Stomach cramps
• Nausea
• Fatigue
• Loss of appetite
• Weight loss
• Fever (in some cases)

Symptoms may improve temporarily before returning days or weeks later.

Without treatment, illness can persist for weeks or even months.

Why is the source still unknown?

Investigators are interviewing infected individuals to identify common exposures.

Patients are being asked about:

• Restaurants they visited
• Grocery stores where they shopped
• Foods they consumed
• Recent travel
• Dates of possible exposure

At present, investigators have not identified a single food item or supplier responsible for the outbreak.

According to the CDC, there is currently no confirmed nationwide source linking all reported cases.

Which foods are commonly linked to Cyclospora?

Previous U.S. outbreaks have frequently been associated with fresh produce, particularly:

• Lettuce
• Cilantro
• Basil
• Raspberries

Because fresh fruits and vegetables are often eaten raw, they can transmit the parasite if contaminated before reaching consumers.

Experts emphasize that no specific produce item has yet been identified in the current outbreak.

Why are some restaurants removing lettuce?

As a precaution, some Taco Bell franchise locations in Michigan reportedly stopped serving lettuce while investigators work to identify the outbreak source.

The Michigan Department of Health has also issued guidance recommending careful handling of leafy greens, including:

• Thorough washing
• Proper refrigeration
• Cooking when appropriate

Several major restaurant chains, including Burger King, Popeyes, Wendy’s, Dunkin’, and Jimmy John’s, have stated they are not aware of any impact on their supply chains.

How is Cyclospora diagnosed?

Unlike many common gastrointestinal illnesses, Cyclospora is not always detected through routine stool testing.

Doctors must specifically request laboratory tests capable of identifying the parasite.

Because of this, infectious disease experts believe reported case numbers likely underestimate the true scale of the outbreak.

How is cyclosporiasis treated?

The standard treatment is prescription antibiotics.

According to the CDC, appropriate antibiotic therapy usually shortens the illness and reduces the risk of prolonged symptoms.

People experiencing persistent diarrhea should:

• Stay well hydrated.
• Seek medical attention if symptoms last longer than several days.
• Contact a healthcare provider if symptoms worsen or signs of dehydration develop.

Young children, older adults, and people with weakened immune systems face a higher risk of complications.

How can people reduce their risk?

Although the source remains unidentified, experts recommend several precautions:

• Wash fresh produce thoroughly under running water.
• Practice good hand hygiene before preparing food.
• Avoid drinking untreated water.
• Refrigerate perishable foods promptly.
• Seek medical care for prolonged gastrointestinal illness.

It’s important to note that washing produce may reduce some contamination but may not completely eliminate Cyclospora, which can adhere tightly to certain fruits and vegetables.

Why this outbreak matters

Cyclosporiasis is relatively uncommon in the United States, making the rapid increase in cases particularly notable.

Michigan typically reports only about 50 cases annually, making this year’s surge unusual enough to trigger extensive state and federal investigations.

Until investigators identify the source, public health officials say consumers should remain alert to symptoms rather than avoid specific foods that have not been linked to the outbreak.

TL;DR

• A growing Cyclospora outbreak is affecting multiple U.S. states, with Michigan reporting the highest number of cases.
• The parasite causes severe watery diarrhea, stomach cramps, nausea, fatigue, and weight loss.
• Health officials have not yet identified the source of the outbreak.
• Previous outbreaks have been linked to fresh produce such as lettuce, cilantro, basil, and raspberries.
• Prompt medical evaluation and antibiotic treatment can significantly shorten the illness.