NEW YORK — Cases of cyclospora, a parasite known for causing diarrhea, are on the rise, with data indicating that 2026 is on track to be the worst year for reported cases in the U.S.
This year, infections have been reported in over 30 states, with numbers already exceeding the previous U.S. record of approximately 4,700 cases set in 2019. While the illness is generally not life-threatening, it is usually treated with antibiotics.
Officials have yet to determine the exact cause of the infections. On Tuesday, federal health authorities noted that infection patterns might differ regionally but suspect a link between cases in Michigan, Ohio, Kentucky, and West Virginia.
Michigan officials blame lettuce
In Michigan, where more than 3,300 cases have been reported, lettuce or salad greens are suspected as potential sources.
After interviewing over 1,000 patients, Natasha Bagdasarian, the chief medical executive of the Michigan health department, stated that “early information has shown lettuce as a common product that regularly comes up during the investigation.”
Given this commonality and considering that produce has been a source of cyclospora outbreaks in the past, Michigan officials recommend buying whole heads of lettuce, discarding the outer leaves, and thoroughly washing the rest. They also advise against using bagged lettuce and pre-mixed salad kits.
On Tuesday, Taco Bell announced it had “voluntarily and temporarily removed limited ingredients at select restaurants as a precautionary measure” and committed to monitoring the situation closely and adhering to public health guidance.
During a call with reporters, federal health officials did not address whether Taco Bell or any particular food vendor or distributor is under investigation.
“The FDA is continuing its traceback investigation on multiple produce items, including locations reported by case patients before they became ill,” stated Donald Prater, Acting Deputy Commissioner for Food at the U.S. Food and Drug Administration.
Cyclospora causes ‘explosive’ diarrhea
Cyclospora is a microscopic parasite that often causes watery diarrhea, sometimes with explosive bowel movements, according to the U.S. Centers for Disease Control and Prevention. Outbreaks typically occur in late spring and summer.
The parasite infects the intestines and spreads through fecal contamination. Previously, infections have occurred from consuming fruits or vegetables irrigated with contaminated water.
Cyclosporiasis, the illness caused by the parasite, is less common than other foodborne illnesses like salmonella and E. coli. Many cases go unlinked to a specific source, and few outbreaks were reported in the U.S. until the last decade when cases began increasing, especially notable in 2018 and 2019.
Experts believe cyclospora cases were historically underreported due to common tests not being designed to detect it. The rise in cases is attributed to climate change and improved detection methods.
2019 was the worst year for infections
In 2019, the U.S. experienced its worst year for cyclospora infections, with about 4,700 reported cases according to federal data on confirmed and suspected cases.
The Centers for Disease Control and Prevention maintains these statistics, although they often lag behind numbers from local health departments. On Tuesday, CDC officials released a health alert reporting 1,645 confirmed domestic cases since May 1, with more than 5,100 requiring further analysis to confirm if they were acquired domestically. Reports have come from 34 states, with no deaths reported.
The true number of cases is likely higher, as some individuals with milder symptoms may not seek medical care, said Gwen Biggerstaff, Deputy Director of CDC’s Division of Foodborne, Waterborne, and Environmental Diseases, during a call with reporters.
It may take days to weeks for symptoms to appear after exposure to the parasite, and it’s uncertain how many are currently being infected or if exposures occurred earlier. However, Biggerstaff expects case numbers to continue rising through August.
The CDC also shared information about an outbreak investigation affecting four states.
The federal alert did not specify the number of reports from each state. Michigan has reported over 3,300 cases, northwest Ohio more than 1,100, New York City over 400, and Illinois more than 200.
Not all cases are believed to be from a common source. In Illinois, for example, over half the infected individuals had traveled outside the U.S., potentially contracting the infection elsewhere.
Michigan officials suspect a significant portion of their cases may be linked to a domestic outbreak. However, CDC officials have not elaborated on why they think cases in Michigan, Ohio, Kentucky, and West Virginia are connected.
— Mike Stobbe
Associated Press reporter Dee-Ann Durbin in Detroit contributed to this report.
