IN-DEPTH CLINICAL REVIEW
Overview.
Cyclosporiasis is an intestinal infection caused by Cyclospora cayetanensis, a coccidian protozoan parasite transmitted exclusively by the faecal-oral route via contaminated fresh produce or water, with no known animal reservoir. The United States is currently experiencing its largest recorded cyclosporiasis season: more than 6,700 confirmed or probable cases had been reported to CDC by mid-July 2026, against roughly 2,700 for the whole of 2025, and the agency is separately reviewing over 5,100 additional reports to determine whether they belong to the same surge.1,2
The rise includes an outbreak of 1,644 infections and 94 hospitalisations linked to shredded iceberg lettuce supplied by Taylor Farms de Mexico and served at Taco Bell locations in five states, which prompted a 17 July 2026 recall. 3
The much larger domestic surge, 1,645 lab-confirmed cases across 34 states (most recent CDC Health Alert Network notice) has no identified single source, and is best described as a seasonal variation of a chronic food-safety vulnerability that has produced outbreaks in the United States almost every year since the mid-1990s. 4
Epidemiology
The current outbreak
Cyclosporiasis has been nationally notifiable in the United States since January 1999, following large multistate outbreaks in 1996 and 1997. By 2015 it was reportable in 44 jurisdictions covering 42 states, the District of Columbia and New York City.
CDC designates 1st May to 31st August as the annual “cyclosporiasis season,” reflecting both the temperature dependence of oocyst sporulation (22–32°C) and the seasonal concentration of fresh imported produce consumption.5,6
The 2026 season is exceptional in scale. Domestically acquired, laboratory-confirmed cases reported since 1 May 2026 (1,645, across 34 states) are more than six times the 249 cases reported over the equivalent period in 2025. No deaths were reported. CDC surveillance discovered a further 440 travel-associated cases.4,7
The Taco Bell/Taylor Farms de Mexico cluster is the only one, within this surge, with a firmly identified food source. FDA and CDC traceback and epidemiological analysis linked illnesses in Indiana, Kentucky, Michigan, Ohio and West Virginia to shredded iceberg lettuce from a single supplier. Taylor Farms de Mexico voluntarily withdrew, then formally recalled, all iceberg lettuce sourced from central Mexico on 17 July 2026.
The CDC states explicitly that the true number of illnesses is likely higher than reported figures given cyclosporiasis’s typical under-diagnosis, and that the outbreak may extend to states without yet-confirmed cases.1,9
Three decades of recurring US outbreaks
Cyclospora emerged as a recognised US food-borne pathogen in the mid-1990s, beginning with a large 1996 multistate outbreak traced to Guatemalan raspberries.
Since then, US outbreaks have recurred in most years, typically clustering in spring and summer and typically implicating imported fresh produce that is eaten raw and difficult to wash thoroughly: raspberries, basil, cilantro, mesclun, snow peas, sugar snap peas, cabbage, parsley, broccoli, green onions, blackberries, watercress, mango and prepackaged vegetable and salad trays have all been implicated across outbreaks since 1995.10,11,12
Prior events include a 2018 outbreak exceeding 2,299 cases across 33 states (about a third linked to prepackaged vegetable trays and fast-food salads), a 2019 multistate outbreak linked to fresh basil that reached over 2,400 cases across the US and Canada, and a 2022 Florida outbreak linked to contaminated lettuce in salad kits that affected more than 500 people. Only a handful of US outbreaks over the past two decades have exceeded 1,000 cases; 2026 is on course to be the largest on record.12,13
Why outbreaks keep recurring. Public Health opinion attributes the rising frequency over the past decade partly to improved clinician awareness and diagnostic testing, and partly to environmental conditions, including warmer temperatures that favour oocyst sporulation and survival. Climate changes might be expanding the window and geographic range for outbreaks.
Because no universally deployed molecular typing tool existed for C. cayetanensis until relatively recently (see Microbiology, below), many temporally clustered cases historically could not be conclusively linked to a single source, meaning the true count of discrete outbreaks within any given season has likely been under-estimated for most of the parasite’s history as a notifiable US disease.6,14
