CDC Investigates Cyclospora Parasite Outbreak: Over 400 Cases Across 18 US States

Major Cyclosporiasis Outbreak Prompts Nationwide Investigation

The US Centers for Disease Control and Prevention (CDC) is leading a multi-state investigation into a growing outbreak of cyclosporiasis, a parasitic intestinal illness that has already infected more than 400 people across 18 states. The outbreak, which began in early May 2026, has intensified sharply in recent weeks, particularly in Michigan, New York, Texas, and Illinois.

Health officials warn that the true number of cases is likely higher than reported, as many individuals with mild symptoms may not seek medical care or get tested for the parasite. The CDC, together with the US Food and Drug Administration (FDA) and state health departments, is working urgently to identify the source of contamination.

What Is Cyclosporiasis?

Cyclosporiasis is a diarrheal illness caused by infection with the microscopic parasite Cyclospora cayetanensis. Unlike many foodborne pathogens, Cyclospora is not typically transmitted directly from person to person. Instead, it spreads when people consume food or water contaminated with feces containing the parasite.

The parasite is commonly found in tropical and subtropical regions, but in recent years, outbreaks have become increasingly frequent in the United States during the spring and summer months. Past outbreaks have been linked to fresh produce such as basil, cilantro, mesclun lettuce, raspberries, snow peas, and berries—often imported from countries where Cyclospora is endemic.

Outbreak by the Numbers

According to the CDC, 145 confirmed cases were reported across 17 states between May 1 and June 16, 2026. Of those, 20 individuals required hospitalization. However, the situation has escalated dramatically. Michigan alone has reported more than 300 cases since June 22, a staggering figure for a state that typically identifies only about 50 cases of cyclosporiasis in an entire year.

• Michigan: Over 300 cases since June 22, concentrated in seven counties including Monroe (70+ cases), Lenawee (33), and Washtenaw (21)
• New York: 107 cases since May 1, with New York City cases roughly doubling compared to the same period in 2025
• Texas, Illinois: Significant number of cases reported, under active investigation
• Other affected states: Alaska, Colorado, Connecticut, Florida, Georgia, Louisiana, Massachusetts, New Jersey, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, Wisconsin
• Age range: 8 years to 84 years (average age: 44.3)

Symptoms to Watch For

Symptoms of cyclosporiasis typically appear two to 14 days after ingesting the parasite. The hallmark symptom is watery diarrhea that can be frequent and explosive. Other common symptoms include:

• Loss of appetite and weight loss
• Abdominal cramps and bloating
• Nausea and vomiting (less common)
• Low-grade fever
• Fatigue and general malaise

In otherwise healthy individuals, the illness may resolve on its own within a few days to weeks. However, without treatment, symptoms can persist for a month or longer and may relapse. The infection is treatable with specific antibiotics, so anyone experiencing persistent watery diarrhea should seek medical evaluation.

No Single Source Identified Yet

What makes this outbreak particularly concerning for health officials is that no single contaminated food source has been identified. The CDC reports no immediate evidence of a single multi-state outbreak linking all cases, which means investigators are working to identify various potential clusters and sources of illness across multiple states simultaneously.

The seasonal timing is a complicating factor. During spring and summer, people consume more fresh produce—including basil, cilantro, spinach, and berries—all of which have been linked to past Cyclospora outbreaks. Imported produce from countries where sanitation standards may differ remains a recurring challenge for food safety regulators.

CDC and State Health Recommendations

Health officials are urging the public to take the following precautions:

• Wash all fruits and vegetables thoroughly under running water before eating, cutting, or cooking
• Scrub firm produce like melons and cucumbers with a clean produce brush
• Cut away damaged or bruised areas on fruits and vegetables before preparing and eating
• Refrigerate cut, peeled, or cooked fruits and vegetables promptly
• Wash hands thoroughly with soap and water before and after preparing food
• See a healthcare provider if you experience sudden, ongoing diarrhea
• Stay hydrated by drinking plenty of water and other fluids if ill

Who Is Most at Risk?

While cyclosporiasis can affect anyone, certain groups may be more vulnerable to severe or prolonged illness. These include young children, older adults, pregnant women, and individuals with weakened immune systems. In immunocompromised patients, the infection can be particularly persistent and may require extended antibiotic treatment.

Frequently Asked Questions

Can cyclosporiasis be spread from person to person?

No. Cyclosporiasis is not known to spread directly from person to person. The parasite requires time outside the body to become infectious (sporulate), so transmission typically occurs through contaminated food or water rather than through casual contact.

How is cyclosporiasis diagnosed?

Diagnosis is made through a laboratory test that examines a stool sample under a microscope. Because the parasite can be difficult to detect, healthcare providers must specifically request testing for Cyclospora—it is not included in routine stool culture panels.

What is the treatment for cyclosporiasis?

The standard treatment is a combination of the antibiotic trimethoprim-sulfamethoxazole (TMP-SMX). For those with sulfa allergies, alternative treatments are available. Early diagnosis and treatment can significantly shorten the duration of illness.

How long does the illness last?

Without treatment, symptoms may last from a few days to a month or longer. With appropriate antibiotic treatment, most patients improve significantly within days. However, relapses can occur.

Should I avoid fresh produce?

No. Health officials do not currently advise avoiding fresh produce altogether. However, thorough washing of all fruits and vegetables is strongly recommended. Cooking produce also kills the parasite. The key is proper food hygiene, not elimination of healthy foods from your diet.

Bottom Line

The current cyclosporiasis outbreak is a significant public health concern, with case numbers far exceeding typical seasonal patterns. While the illness is rarely life-threatening, it causes considerable discomfort and may require medical treatment. The CDC and state health departments continue their investigation, and the public is advised to practice rigorous food hygiene and seek medical attention if symptoms develop.

As summer produce consumption peaks, staying informed and following simple food safety steps can help protect you and your family from this unpleasant—and entirely preventable—infection.

Stay updated with Health Professional Radio for the latest developments in public health and infectious disease news.