A multistate outbreak of cyclosporiasis, a parasitic illness caused by Cyclospora cayetanensis, has sickened at least 145 people across 17 states as of mid-June 2026, according to the Centers for Disease Control and Prevention (CDC). The parasite, which is transmitted through contaminated fresh produce, causes frequent, watery diarrhea that can persist for weeks and often relapses if untreated. Unlike many foodborne pathogens, Cyclospora is not transmitted person-to-person; infection requires consumption of food or water contaminated with mature oocysts. The source of the 2026 outbreak remains unidentified.
Michigan has experienced a particularly sharp escalation, with more than 150 cases identified since the two-week old CDC report, suggesting regional distribution of the contaminated product. Historically, cyclosporiasis outbreaks in the U.S. have been linked to imported fresh produce such as basil, cilantro, raspberries, and bagged salads. Diagnosis requires specific laboratory testing, and treatment with trimethoprim-sulfamethoxazole is highly effective. Consumers should stay informed of recalls, wash produce thoroughly, and seek medical care for prolonged diarrheal illness, especially during summer months when cases peak.
The Parasite and Its Transmission
Cyclospora cayetanensis is a single-celled, obligate intracellular parasite that completes its life cycle within the human host. The parasite is transmitted through the fecal-oral route, typically via consumption of food or water contaminated with feces. A critical feature of its epidemiology is that the parasite requires a period of maturation outside the host: Cyclospora oocysts shed in feces must sporulate, or be released, in the environment, a process requiring one to several weeks under favorable conditions, before they become infectious. Consequently, direct person-to-person transmission is considered unlikely.
The parasite is endemic in tropical and subtropical regions, and historically, cases in the United States were primarily associated with international travel. However, over the past decade, an increasing number of domestically acquired cases have been documented, linked to both imported and domestic fresh produce. The CDC says that the number of reported cases typically rises during the spring and summer, from late May through August. In 2025, for example, 1,180 domestically acquired cases were reported across 38 states, with illness onsets occurring between May and August. The 2026 outbreak follows this established seasonal pattern.
Clinical Presentation, Diagnosis, and Treatment
The clinical manifestations of cyclosporiasis are primarily gastrointestinal. The parasite infects the small intestine and typically causes watery diarrhea with frequent, sometimes explosive, bowel movements. Other common symptoms include loss of appetite, weight loss, abdominal cramping and bloating, increased gas, nausea, and prolonged fatigue. Vomiting, body aches, and low-grade fever may also occur. The incubation period averages approximately one week but can range from two days to two weeks or more.
If untreated, the illness may persist for a few days to over a month and often follows a remitting-relapsing course, in which symptoms appear to resolve only to return. Diagnosis is established through laboratory testing of stool samples. However, detection of Cyclospora requires specialized testing that is not routinely performed in most U.S. laboratories; clinicians must specifically request testing for this parasite. Multiple stool samples may be necessary, as oocysts are shed intermittently.
The recommended treatment is a course of trimethoprim-sulfamethoxazole (TMP-SMX), sold under brand names such as Bactrim, Septra, or Cotrim. For patients allergic to sulfa drugs, alternative treatment options should be discussed with a healthcare provider. Supportive care, including hydration, is also important for managing symptoms. While most immunocompetent individuals will eventually recover without treatment, untreated illness can be prolonged and debilitating.
Recent Outbreaks
Over the past decade, cyclosporiasis outbreaks in the United States have become more frequent and widespread, driven largely by contaminated fresh produce:
- In 2020, a major multistate outbreak linked to Fresh Express bagged salad mix containing iceberg lettuce, red cabbage, and carrots resulted in over 700 reported cases across multiple states.
- The following year saw a sharp increase in cases in Florida, with 254 reported in 2021, which then doubled to 513 the next year, including a large cluster linked to a specific Caesar salad kit sold at a grocery store chain.
- Nationally, cases also spiked dramatically, more than doubling from 537 in 2016 to 1,194 in 2017, then nearly tripling to 3,519 in 2018, and peaking at 4,703 in 2019.
- In 2023, an outbreak in Alabama linked to cilantro from Mexico sickened 47 patrons of a Mexican-style restaurant, and Colorado reported 264 cases.
- The trend continued in 2025, with 1,180 domestically acquired cases and 105 hospitalizations reported across 38 states.
The 2026 Outbreak: Scope and Demographics
According to CDC surveillance data, as of June 16, 2026, 145 domestically acquired cases have been reported. These cases occurred in individuals who became ill after eating food in the United States and who did not report any international travel during the 14 days before symptom onset. The median illness onset date was May 13, 2026, with cases reported between May 1 and June 6. The affected individuals range in age from 5 to 86 years, with a median age of 42. Women account for 61% of cases.
In addition to these domestically acquired cases, 45 travel-associated cases have been reported in individuals who became ill after consuming contaminated food or water while traveling outside the United States. Among these travel-related cases, three individuals required hospitalization. The travel-associated cases ranged in age from 17 to 89 years, with a median age of 43, and 62% were female. No deaths have been reported in either group.
As is common in most foodborne outbreaks, the true number of infections is likely higher than reported, as some individuals may recover without seeking medical care and may not be tested for Cyclospora.
Investigation and Source Identification
The source of the 2026 outbreak remains unidentified. The FDA has initiated a traceback investigation to identify the contaminated product.
Historically, cyclosporiasis outbreaks in the United States have been linked to various types of fresh produce, including basil, cilantro, mesclun lettuce, raspberries, and snow peas. Bagged salad mixes have also been implicated. The parasite is often associated with imported produce from countries where it is endemic, though domestic farms have also been identified as sources.
Prevention and Public Health Measures
Preventing cyclosporiasis presents unique challenges. Routine chemical disinfection or sanitization methods are unlikely to kill Cyclospora oocysts on produce. The most effective preventive measure is to avoid consuming food or water that may be contaminated with feces.
Experts recommend that consumers follow standard food safety practices: washing hands with soap and water before and after handling raw produce; washing all fruits and vegetables thoroughly under running water before eating, cutting, or cooking; scrubbing firm produce with a clean brush; and refrigerating cut, peeled, or cooked produce promptly. However, it is important to note that washing produce may reduce but does not eliminate the risk of Cyclospora infection.
For healthcare providers, the CDC emphasizes the importance of considering Cyclospora as a potential cause of prolonged diarrheal illness, particularly in patients with a history of travel to endemic areas or during the summer months when domestic cases peak. Clinicians should specifically request testing for Cyclospora, as routine stool testing does not typically include this parasite.
Analysis and Next Steps
What is new about the 2026 cyclosporiasis outbreak is its scale and the ongoing uncertainty regarding its source. While cyclosporiasis is a recognized seasonal illness, the rapid accumulation of 145 confirmed domestically acquired cases across 17 states, with 20 hospitalizations as of June 16, 2022, has elevated it to a significant public health concern. The investigation by the FDA and CDC is ongoing, but the fact that the source remains unidentified weeks into the outbreak underscores the complexity of traceback investigations for fresh produce, which often involve intricate and globalized supply chains.
In Michigan, state health officials are reporting an even more dramatic surge, with more than 150 cases identified in the state alone in just over a week. The first case in Michigan was identified on June 22, 2026, and in the eight following days, dozens more cases were identified. More than a dozen Michigan residents have been hospitalized. A press release from the Michigan Department of Health and Human Services, stated that the department is working with local health departments in southeastern Michigan to investigate the sudden and large increase in cyclospora cases and identify a common exposure. This rapid escalation in a single state suggests that the contaminated product may have been distributed regionally or consumed at a common event, though the source remains unidentified.
Why this matters is that cyclosporiasis is a debilitating illness that can lead to prolonged suffering, dehydration, and, in severe cases, hospitalization. The parasite’s ability to cause relapsing symptoms means that those affected may face weeks of illness, impacting their ability to work, care for family members, and maintain their daily routines. The fact that the outbreak is domestically acquired highlights vulnerabilities in the U.S. food supply and the need for robust surveillance and rapid response systems. The 2025 season saw 1,180 domestically acquired cases across 38 states, with 105 hospitalizations, demonstrating that cyclosporiasis is a recurring public health challenge.
Who is affected is a broad cross-section of the population, ranging from children to the elderly, though the median age of 42 suggests that working-age adults are significantly impacted. The higher proportion of cases among women (61%) may reflect differences in food consumption patterns or exposure risks, though further investigation is needed. The 20 hospitalizations indicate that while the disease is not usually fatal, it can be severe enough to require intensive medical care. In Michigan, the rapid escalation of cases, from zero reported on June 18 to more than 150 in just over a week, demonstrates how quickly a contaminated product can spread illness across a population.
What to do now requires a coordinated response. For public health agencies, the immediate priority is to continue the traceback investigation to identify and remove the contaminated product from the market. Enhanced surveillance, including the use of molecular tools to link cases, is essential for detecting clusters and identifying sources more quickly. For healthcare providers, prompt diagnosis and treatment with TMP-SMX are critical to reducing the duration and severity of illness. For consumers, the most important step is to stay informed about the outbreak and any recalls. Washing produce thoroughly, though not a guarantee against Cyclospora, remains a recommended practice. The best defense, however, is a food safety system that prevents contamination at the source. The lessons learned from the 2026 outbreak, particularly the rapid escalation in Michigan, will be crucial for strengthening those defenses against future summer outbreaks.
