Public health officials are investigating a rapidly expanding outbreak of cyclosporiasis across the United States, with reports of infections surfacing in 34 states. As of mid-July 2026, the Centers for Disease Control and Prevention (CDC) has confirmed 1,645 domestically acquired cases since the start of the annual season on May 1. An additional 5,100 cases are currently under analysis to determine if they are linked to the same parasitic illness.
The current surge represents a significant increase compared to national data from the same period in 2025, which saw 249 cases. While 141 individuals have been hospitalized, no deaths have been reported. Experts note that because the illness is often underdiagnosed and underreported, the actual number of infections is likely higher than the current figures suggest.
Lettuce Identified as a Potential Culprit
Michigan state health officials are currently narrowing their investigation toward lettuce and prewashed salad kits as a possible source for the regional outbreak. Dr. Natasha Bagdasarian, Michigan’s chief medical executive, stated that early signals from the state’s review of cases implicate lettuce.
While Michigan is experiencing a high volume of cases—reporting over 3,300 by mid-July—other states including Ohio, West Virginia, Kentucky, Illinois, New York, and North Carolina have also reported significant numbers of infections. The CDC is currently monitoring at least one specific cluster of more than 400 cases across four states, which appear to be epidemiologically linked. However, officials cautioned that there may be multiple, unrelated outbreaks occurring simultaneously across the country.
For more on this story, see Historic Cyclosporiasis Outbreak Surges Across 17 States.
Understanding the Cyclospora Parasite
Cyclosporiasis is a gastrointestinal illness caused by the microscopic parasite *Cyclospora cayetanensis*. The infection is typically transmitted through the consumption of food or water contaminated with feces containing the parasite. It is not generally spread from person to person, as the parasite typically requires one to two weeks in the environment after being shed in stool to become infectious.
Symptoms of the infection usually appear 2 to 14 days after exposure, with a median onset of about one week. The most common symptom is sudden, watery, and frequent diarrhea, often described as “explosive.” Other symptoms may include:
- Loss of appetite and weight loss
- Bloating and nausea
- Fatigue
- Vomiting and low-grade fever (less common)
Without treatment, the illness can follow a remitting-relapsing course lasting from a few days to a month or longer. While generally not life-threatening, complications can include malabsorption, cholecystitis, and reactive arthritis.
Challenges in Investigation and Detection
Investigating *Cyclospora* presents unique challenges for public health authorities. Unlike bacteria such as *Salmonella* or *E. coli*, *Cyclospora* cannot be grown in laboratory cultures, which prevents the use of standard subtyping tools like whole-genome sequencing to easily trace the source of an outbreak. The CDC is currently relying on partial genotyping to connect cases, though officials note that the parasite’s genome is complex. Furthermore, standard ova and parasite (O&P) exams are often unreliable for detecting the parasite.
This follows our earlier report, CDC Warns of Cyclosporiasis Outbreak Affecting 31 States Hospitalizing 86.
Clinical Guidance and Surveillance
The current outbreak is being monitored by the CDC in coordination with the FDA and state health departments. Because the typical *Cyclospora* season runs from May 1 through August 31, officials expect case counts to continue rising as data is received, noting a typical reporting lag of approximately six weeks. As investigations continue, health officials maintain that the source of the contamination remains officially unidentified.
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