Explosive Diarrhea Illness Reported Across US, See Map of Affected States

Quick Answer

A parasitic illness caused by Cyclospora cayetanensis has been linked to over 145 cases of explosive diarrhea across 17 U.S. states as of early July 2026.

The Centers for Disease Control and Prevention (CDC) has identified New York, Illinois, and Texas as the states with the highest case counts. The outbreak is being tracked primarily during the peak transmission season from May to August, with infections reported in states including Louisiana, Ohio, and Michigan.

Key Facts

• At least 145 people have been infected with Cyclospora across 17 states in the current outbreak.
• New York, Illinois, and Texas are reporting the most cases, though specific state-level totals beyond partial data are not fully public.
• The illness causes explosive and watery diarrhea, along with other gastrointestinal symptoms.
• Transmission typically occurs through contaminated food, especially fresh produce like raspberries, basil, and lettuce.
• The CDC is actively investigating the outbreak, which is most active between May and August each year.
• Cases have been confirmed in states including California, Connecticut, Illinois, Indiana, Michigan, Nebraska, and Louisiana, in addition to others not yet publicly listed by state.
• Cyclospora is a microscopic parasite that requires laboratory testing for diagnosis, as symptoms can mimic other gastrointestinal infections.

Understanding the Parasite Behind the Outbreak

Cyclospora cayetanensis is a single-celled parasite that causes cyclosporiasis, an intestinal infection. Unlike bacteria or viruses, this parasite is not typically transmitted from person to person.

Instead, infection occurs when someone ingests food or water contaminated with mature Cyclospora oocysts—the parasite's infectious form. The oocysts are shed in the stool of infected individuals and must mature in the environment (a process called sporulation) before they can infect another person.

This means that direct contact with an infected person rarely causes spread, which is a key distinction from pathogens like norovirus or E. coli.

The parasite's biology explains why outbreaks often cluster around specific food items. Once oocysts contaminate produce during growing, harvesting, or processing, they can survive for weeks in cool, moist conditions.

Fresh fruits and vegetables—especially those imported from regions where Cyclospora is endemic—are common vehicles. In the United States, past outbreaks have been traced to raspberries from Guatemala, basil from Mexico, and lettuce from multiple sources.

Consumers cannot tell if produce is contaminated by sight or smell, making prevention difficult without proper washing and cooking. The incubation period for cyclosporiasis is typically about one week, though it can range from two to fourteen days.

This delay between exposure and symptom onset complicates investigations. By the time a person becomes ill, the contaminated food may have been consumed or discarded, making it harder for health officials to trace the source.

The CDC and state health departments rely on patient interviews about food history, but recall bias—people forgetting what they ate days earlier—often hampers these efforts.

Why the Outbreak Peaks in Summer

The current outbreak's timing from May to August aligns with Cyclospora's seasonal pattern in the United States. Several factors contribute to this summer surge.

First, warm and humid conditions favor oocyst maturation in the environment. While the parasite does not replicate outside a host, higher temperatures accelerate sporulation, making the oocysts infectious more quickly.

Second, summer is peak season for fresh produce consumption, including items like berries, salads, and herbs that are often eaten raw. Third, many imported fruits and vegetables arrive from regions where Cyclospora is endemic, such as Central and South America, and these imports increase during warmer months.

Climate change may also be extending the transmission window. Warmer average temperatures in spring and fall could allow oocysts to survive longer at northern latitudes, potentially expanding both the geographic range and duration of outbreaks.

However, the current 17-state pattern remains concentrated in areas with higher produce import volumes and population density, which explains why New York, Illinois, and Texas report the most cases. The CDC's surveillance system for cyclosporiasis relies on passive reporting from healthcare providers and laboratories.

This means that mild cases—those that do not require medical attention—are likely undercounted. For every confirmed case, there may be several unreported infections.

The true number of people affected by the current outbreak could be significantly higher than 145. Because Cyclospora is not a nationally notifiable disease in all states, reporting requirements vary, and some states may not routinely test for it unless a clinician specifically requests the test.

Symptoms, Diagnosis, and Treatment

The hallmark symptom of cyclosporiasis is watery diarrhea that can be explosive and profuse. Patients often describe multiple episodes per day, leading to dehydration and electrolyte imbalances.

Other common symptoms include stomach cramps, bloating, nausea, vomiting, low-grade fever, and fatigue. The illness can last from a few days to several weeks if untreated, and relapses are possible.

In severe cases, malabsorption and weight loss can occur, particularly in immunocompromised individuals or those with prolonged infections. Diagnosis requires a specialized laboratory test called a modified acid-fast stain or polymerase chain reaction (PCR) assay of a stool sample.

Standard stool cultures for bacteria or ova and parasites often miss Cyclospora because the oocysts are small and do not stain well with conventional methods. This diagnostic gap means that clinicians must suspect cyclosporiasis based on travel history, food exposure, and symptom patterns.

The CDC recommends testing for Cyclospora in patients with watery diarrhea lasting more than three days, especially if they have consumed fresh produce commonly linked to outbreaks. Treatment is straightforward: a course of the antibiotic trimethoprim-sulfamethoxazole (TMP-SMX), commonly known as Bactrim or Septra.

This medication is highly effective at eliminating the parasite and shortening the duration of illness. For patients who are allergic to sulfa drugs, alternatives such as ciprofloxacin or nitazoxanide may be used, though their efficacy is less well-established.

Supportive care—including oral rehydration solutions and electrolyte replacement—is important to manage dehydration. Most otherwise healthy individuals recover fully with treatment, though the illness can be debilitating during the acute phase.

One challenge in managing outbreaks is the delay between exposure and treatment. Because the incubation period is a week or longer, patients may seek care after the illness is already well-established.

Early treatment reduces symptom severity and duration, but many people do not see a doctor until symptoms are severe. Public health messaging that emphasizes the importance of seeking medical care for persistent watery diarrhea—especially during summer months—can help reduce complications and speed source identification.

States Most Affected and Investigation Efforts

Based on the available data, New York, Illinois, and Texas are the states with the highest number of confirmed cases in the current outbreak. However, partial reports also list individual case counts for other states: California has reported three cases, Connecticut two, and Illinois, Indiana, Michigan, Nebraska, and New York have reported one case each from certain subsets of data.

These numbers likely represent only a portion of the total, as the CDC continues to collect and verify reports from all 17 affected states. The geographic distribution reflects both population density and food import patterns.

Large metropolitan areas like New York City, Chicago, and Houston serve as major distribution hubs for imported produce. If the contamination occurred at a central point—such as a specific farm, packing facility, or distribution center—cases would cluster in regions that receive shipments from that source.

The CDC's investigation likely involves traceback efforts to identify the common food item linked to illnesses, though no specific product has been publicly named as of July 2026. State health departments are conducting interviews with patients to collect detailed food histories.

Common questions include consumption of fresh produce, restaurant meals, and imported items in the two weeks before symptom onset. Investigators also look for clusters of cases linked to specific grocery chains, farmers' markets, or restaurants.

In past outbreaks, rapid identification of a common source allowed for product recalls and public warnings that prevented further infections. For example, in 2018, an outbreak linked to prepackaged vegetable trays was traced to a single producer, leading to a nationwide recall.

The involvement of Louisiana in the outbreak is notable because the state has a warm climate that could theoretically support local transmission, though most U.S. cases are linked to imported produce.

Louisiana's cases may reflect contamination that occurred elsewhere, with infected individuals traveling or consuming food purchased within the state. The CDC's outbreak investigation page typically updates weekly, so residents in affected states should monitor local health department alerts for potential food safety warnings.

Frequently Asked Questions

What exactly causes explosive diarrhea in this outbreak?

The illness is caused by the parasite Cyclospora cayetanensis, which infects the small intestine and leads to watery, explosive diarrhea. It is not caused by a virus or bacteria, which means it requires different treatment (antibiotics) than typical gastroenteritis.

How is it spread?

Cyclospora is spread by ingesting food or water contaminated with the parasite's oocysts. It is not spread directly from person to person because the oocysts need time outside the body to become infectious.

Contaminated fresh produce—especially raspberries, basil, lettuce, and other raw fruits and vegetables—is the most common source in U.S. outbreaks.

Who is at greatest risk?

Anyone who consumes contaminated food can become infected, but people with weakened immune systems, young children, and older adults may experience more severe symptoms. Travelers to regions where Cyclospora is endemic (like tropical and subtropical areas) are also at higher risk.

How can I prevent infection?

Wash all fresh produce thoroughly under running water before eating, even if you plan to peel it. Cooking kills the parasite, so thoroughly cooked vegetables are safe.

Avoid raw or undercooked produce imported from countries with poor sanitation, especially during the summer peak season. There is no vaccine for cyclosporiasis.

When should I see a doctor?

Seek medical care if you have watery diarrhea that lasts more than three days, especially if accompanied by severe cramps, fever, or signs of dehydration (dry mouth, decreased urination, dizziness). Mention to your doctor that you suspect possible Cyclospora exposure, as specific testing is required for diagnosis.

Reference Notes

Information in this article is based on publicly available sources. Some details may change over time.

Verify with official sources before acting. The CDC's outbreak investigation page and state health department alerts provide the most current data on case counts and affected locations.