CDC closes out worst cyclosporiasis season on record, with more than 18,000 cases tied largely to tainted lettuce

The Centers for Disease Control and Prevention posted a season-ending tally this week showing 2026 was by far the worst year on record for cyclosporiasis, the intestinal illness caused by the parasite Cyclospora cayetanensis. According to case data the agency updated Tuesday, state and local health departments reported 18,445 laboratory-confirmed, domestically acquired infections between May 1 and Aug. 31, the period the CDC defines as the annual cyclosporiasis season.

That is roughly fifteen times the 1,180 cases the agency counted over the same stretch in 2025. The 2026 season also produced 990 hospitalizations and two deaths, both in Michigan, across 49 states and the District of Columbia. A separate CDC count found an additional 1,900 confirmed infections among travelers who were likely exposed outside the United States.

The numbers behind the surge

Much of the spike traces to a single, unusually large source: iceberg lettuce grown in central Mexico and processed by Taylor Farms de Mexico. In a multistate outbreak investigation the CDC opened in July, the agency and its state partners linked 11,458 illnesses across 20 states to that lettuce, with at least 495 hospitalizations. Genetic sequencing of Cyclospora samples from sick people in different states showed the parasites were closely related, and roughly 90 percent of 190 patients interviewed in detail said they had eaten iceberg lettuce shortly before falling ill, according to the agency's investigation notes.

The Food and Drug Administration's parallel investigation traced the contamination to Taylor Farms de Mexico's central Mexico supply chain and found the product had reached Walmart stores under the Marketside brand, as well as Taco Bell and Jack in the Box locations and foodservice distributors including Sysco. The company issued a voluntary recall notice on July 17 covering all iceberg lettuce sourced from that region, including bagged salad and shredded lettuce with best-by dates through Aug. 3. The FDA classified the action as a Class I recall, its most serious designation, reserved for products with a reasonable probability of causing serious injury or death.

How the outbreak took hold

Cyclospora is a single-celled parasite that spreads through contaminated food or water rather than person to person, and produce grown or processed in regions without reliable irrigation and sanitation controls has repeatedly been implicated in past U.S. outbreaks tied to imported herbs and leafy greens. The CDC has also issued a health advisory to clinicians urging them to consider cyclosporiasis in patients with prolonged watery diarrhea, particularly given that routine stool tests do not always detect the parasite and specialized testing is often required. Symptoms typically begin about a week after exposure and can include watery diarrhea, cramping, bloating, fatigue and loss of appetite. Left untreated, illness can drag on for weeks or return in cycles even after apparent improvement, and the CDC advisory notes that a specific antibiotic combination, rather than supportive care alone, is generally needed to clear the infection.

The lettuce-linked cluster does not account for the full national total. The CDC and FDA say they are separately investigating at least six other clusters of cyclosporiasis for which a source has not yet been confirmed, meaning a meaningful share of this season's caseload remains unexplained. The agency also cautions that its own numbers are still incomplete: because it can take roughly six weeks from when someone first gets sick to when a confirmed case is reported to the CDC, the season-ending count is likely to keep climbing for weeks after the official season closes. Similar revisions have followed past cyclosporiasis seasons, when totals reported in early autumn were pushed higher well into the winter as delayed diagnoses worked their way through state laboratory systems.

Who has been affected

The CDC's demographic breakdown shows a median patient age of 46, with women accounting for 57 percent of confirmed cases. Michigan has been the hardest-hit state throughout the outbreak, and health officials there recorded both of the season's fatalities. Illness onsets in the lettuce-linked cluster ran from mid-June through mid-August, tracking closely with the period the contaminated product was in distribution before the recall took effect.

Because the recalled lettuce moved through both retail and foodservice channels, the exposure was not limited to home cooks. Diners who ate at affected Taco Bell and Jack in the Box locations before the recall, along with Walmart shoppers who bought Marketside-brand salad or shredded lettuce with the affected best-by dates, were among those the CDC and FDA identified as having been exposed. Restaurant chains and the grocer have not disclosed how many individual locations received the recalled product, and neither has said publicly how many confirmed illnesses, if any, were traced specifically to their outlets rather than to retail purchases.

Food-safety reporting on the outbreak, including coverage by the University of Minnesota's Center for Infectious Disease Research and Policy, has tracked the case count climbing in weekly increments over the summer as more state labs confirmed diagnoses and CDC absorbed the backlog. That pattern is typical of cyclosporiasis surveillance, where confirmation lags noticeably behind actual illness.

"The shredded lettuce that was connected to the cases of cyclosporiasis by epidemiological data is off the market," said Kalmia Kniel, a food microbiologist at the University of Delaware, adding that "there are no cases linked to bagged leafy green products at this time."

What happens next

Kniel's assessment, reported this week, reflects the FDA's own position that all recalled lettuce tied to the Taylor Farms cluster has aged out of the supply chain and is no longer available for purchase. Food-safety specialists are advising consumers to keep basic precautions in place even so: choosing whole heads of lettuce over precut and bagged greens where possible, thoroughly washing produce, cooking vegetables when practical since heat destroys the parasite, and favoring fruit with a protective peel, such as bananas, avocados or citrus. Produce with complex, hard-to-rinse surfaces, including cilantro, berries and other soft leafy greens, has been linked to past Cyclospora outbreaks and continues to carry comparatively higher risk.

With the formal cyclosporiasis season now closed, state and federal investigators are expected to keep updating case totals into the fall as delayed lab confirmations arrive, and to continue working the unresolved clusters that fall outside the lettuce recall. The CDC has not said when it expects those additional investigations to conclude.