On July 14, the U.S. Centers for Disease Control and Prevention (CDC) issued a health advisory warning the public of the increase in domestically acquired cyclosporiasis cases reported across the U.S., including a large outbreak cluster in the Midwest.

Since May 1, 2026, CDC has received reports of 1,645 laboratory-confirmed domestically acquired Cyclospora cayetenensis infections spanning 34 states, with more than 5,100 additional cases requiring analysis to determine whether they were also acquired in the U.S. For comparison, during the same period in 2025, CDC had only received 249 reports of domestically acquired cyclosporiasis cases.

Among confirmed case patients with available information, 141 people (9 percent) have been hospitalized, and no deaths have been reported. Patients ranged in age from 2 to 95 years, with a median age of 44 years.

CDC, the U.S. Food and Drug Administration (FDA), and state and local health departments are investigating multiple multistate outbreaks to identify the food sources responsible for the illnesses. According to CDC, cyclosporiasis is often underdiagnosed and underreported, meaning the true number of illnesses is likely higher than currently reported.

CDC Identifies Midwestern Outbreak Cluster

The agency has also opened an outbreak investigation into a cluster of more than 400 cases in at least four Midwestern states—Michigan, Ohio, West Virginia, and Kentucky—with additional cases under investigation. These cases appear to be epidemiologically linked, suggesting a common source of infection.

As of July 14, the Michigan Department of Health and Human Services (MDOH) has reported 3,309 Cyclospora infections and 44 hospitalizations in Michigan alone.

Vehicle of Illness Unconfirmed, Michigan Investigates Lettuce

CDC emphasized that a specific food item has not yet been confirmed as the vehicle of illness. However, previous reporting found that CDC was investigating illness clusters associated with Mexican-style restaurants, a grocery chain, and a catered event. FDA's Coordinated Outbreak Response and Evaluation (CORE) Network has also reportedly been conducting traceback investigations involving white and green onions, cucumbers, and cilantro. In addition to the Midwestern outbreak cluster of more than 400, FDA has listed two other Cyclospora outbreak investigations (one with eight cases and one with 18 cases) on its CORE table. Neither has been linked to a food source yet.

Additionally, Michigan officials informed the public on July 12 that it was investigating lettuce or salad greens as a common product of interest, while noting that these food items are not definitively confirmed as the vehicle(s) of illness. Cyclospora cayetanensis is most commonly associated with fresh produce.

CDC’s Message to Healthcare Providers, Laboratories

CDC urged clinicians to consider Cyclospora infection in patients experiencing prolonged or relapsing watery diarrhea, particularly when symptoms occur during the spring and summer months or when patients report consuming fresh produce. The agency also encouraged healthcare providers to request testing specifically for C. cayetanensis, because the parasite is not routinely detected by standard stool testing panels.

Public health officials asked laboratories and healthcare providers to promptly report confirmed cases to local or state health departments to support ongoing outbreak investigations and traceback efforts.

Although cyclosporiasis is a nationally notifiable disease, CDC cut C. cayetanensis from its Foodborne Diseases Active Surveillance Network (FoodNet) in 2025. Although state health departments are no longer required to surveil for the parasite or any other pathogens eliminated from FoodNet, they can continue to conduct surveillance for those pathogens on their own, if they so choose.

U.S. Cyclospora Cases Are Climbing Year After Year

Since the 1990s, the prevalence of C. cayetanensis has had an upward trajectory, trending toward possible endemicity. As explained by expert Larry Keener, CFS, PA in Food Safety Magazine, domestic cases of Cyclospora infections more than doubled from 537 in 2016 to 1,194 in 2017, and then nearly tripled to 3,519 cases in 2018. Between 2019 and 2022, the number of laboratory-confirmed cases of cyclosporiasis in the U.S. ranged from a high in 2019 of 2,408 cases to a low in 2021 of 1,024 cases. By 2023, there were nearly 3,000 cases of cyclosporiasis reported in the U.S.

Cyclosporiasis is now considered an "important neglected parasitic infection" by CDC. It is also a nationally notifiable disease.

A Challenging Parasite to Detect and Investigate

Parasites like C. cayetanensis are challenging to isolate and identify, as they are not culturable like bacteria and viruses, and infections typically require direct microscopic evidence from stool samples to diagnose, Mr. Kenner explained. These conditions increase the likelihood of failure in identification and contribute to inefficient traceback efforts. Exemplifying the challenge posed by the parasite to public health officials, of the four foodborne illness outbreaks attributed to C. cayetanensis in 2023, three were inconclusive in determining a food source. Similar trends and investigation outcomes were seen in 2022 and 2024.