Since May 1, 2026, More Than 1,645 Confirmed Cases of Cyclosporiasis Have Been Reported Across 34 States. More Than 5,100 Additional Cases Are Under Investigation. The Source Is Shredded Iceberg Lettuce Served at Taco Bell.

Cyclospora cayetanensis is a microscopic intestinal parasite that most clinicians in the United States rarely encounter and even more rarely think to test for. It causes cyclosporiasis, a gastrointestinal illness characterized by prolonged, relapsing watery diarrhea that can last weeks without treatment. It is endemic to tropical and subtropical regions and reaches the United States primarily through contaminated imported produce. Fresh herbs, berries, and leafy greens from Mexico and Central America have been implicated in multiple outbreaks over the past three decades. The current outbreak is the largest domestically acquired cyclosporiasis surge in recent CDC surveillance history, surpassing last year's case count by more than six to one and generating a formal Health Alert Network notice. This week CliniScope Weekly reviews the CDC Health Alert Network notice CDCHAN-00531 and the associated outbreak investigation data. This is a breaking public health event with immediate implications for any clinician seeing patients with persistent diarrhea this summer.

Since May 1, 2026, CDC has received reports of 1,645 confirmed domestic cases of cyclosporiasis across 34 states, with more than 5,100 additional cases requiring further analysis to confirm domestic acquisition. Case-patients ranged in age from 2 to 95 years with a median age of 44 years, and 56% were female. Of confirmed cases with available information, 141 (9%) required hospitalization. No deaths have been reported. This is substantially higher than the 249 cases reported nationally by the same time last year.

Within this broader national surge, a distinct multistate cluster has been epidemiologically linked to shredded iceberg lettuce served at Taco Bell locations in Indiana, Kentucky, Michigan, Ohio, and West Virginia. As of July 16, 2026, 1,644 people with confirmed Cyclospora infections reporting exposure to Taco Bell have been reported from these 5 states. Illness onset dates in the Taco Bell-linked cluster range from May 13 to July 13, 2026, with 94 hospitalizations and no deaths reported. Michigan health officials interviewed 190 of the Taco Bell-linked cases in detail — 90% of those interviewed reported eating iceberg lettuce specifically.

FDA's traceback investigation identified a single supplier of shredded iceberg lettuce from Mexico used at the Taco Bell locations where sick people ate before becoming ill. Taco Bell has committed to stop using lettuce from the identified supplier. FDA has increased border screening for products implicated in the outbreak and continues to work with the supplier to determine whether potentially contaminated product remains in the market.

Cyclosporiasis is caused by Cyclospora cayetanensis. People become infected by consuming food or water contaminated with the parasite. It is not spread directly from person to person. Symptoms typically begin about one week after exposure, with onset occurring two to 14 days after exposure. The most common symptoms are frequent watery diarrhea, loss of appetite, weight loss, bloating, nausea, and fatigue. Without treatment, symptoms can follow a remitting-relapsing course lasting from a few days to a month or longer. Complications can include malabsorption, cholecystitis, and reactive arthritis.

Laboratory detection is where most clinical workups fail. Standard ova and parasite examinations may not reliably detect Cyclospora. CDC is urging clinicians to specifically request Cyclospora testing when it is clinically suspected. Molecular PCR-based testing, where available, improves detection meaningfully. Cyclospora is also resistant to routine chemical disinfection — no EPA-registered disinfectant has been shown to be effective against it.

The six-to-one increase over last year is the number that should concern public health professionals. Cyclospora counts do not surge sixfold without a failure somewhere in the food supply chain. The link to shredded iceberg lettuce from a single Mexican supplier, distributed to Taco Bell locations across five states, is now established by traceback investigation. But the 5,100-plus cases still under analysis nationally suggest this is not a contained single-source event. The broader national surge may involve additional produce sources that have not yet been characterized.

The clinical diagnosis problem is worth naming plainly. A patient who has had three weeks of watery diarrhea, is losing weight, and feels exhausted is not a diagnostic mystery if you think of Cyclospora. The issue is that most clinicians do not think of it, and standard stool panels do not include it unless specifically requested. What tends to happen instead is that the patient gets treated symptomatically, or gets an empiric course of antibiotics that will not touch a parasite, and the correct diagnosis gets delayed. Given that 90% of the Taco Bell-linked cases who were specifically interviewed reported eating iceberg lettuce, a targeted food history in these patients is clinically useful right now.

The treatment is effective and simple once the diagnosis is made. Trimethoprim-sulfamethoxazole (TMP-SMX) for seven to ten days is the recommended regimen for immunocompetent adults and children over two months of age. Longer courses should be considered for patients with immunocompromising conditions. The challenge is ordering the right test before defaulting to supportive care.

The broader food safety dimension of this outbreak is not new. Cyclospora is endemic to the agricultural regions of Mexico where much of the United States fresh produce supply originates. Every cyclosporiasis season is shaped by what is grown, harvested, and shipped from those regions. This outbreak is not an anomaly. It is a recurrence of a structural vulnerability in how the United States sources fresh produce at scale, one that surfaces in the surveillance data with some regularity, and that has not yet prompted the kind of systemic regulatory response that would meaningfully reduce recurrence.

Drawn directly from the CDC Health Alert Network notice CDCHAN-00531:

• —Consider cyclosporiasis in any patient with prolonged or relapsing watery diarrhea during the May through August season, even without a history of international travel.
• —Specifically request Cyclospora laboratory testing on stool specimens. Do not rely on routine ova and parasite examinations alone. Request PCR-based testing where available.
• —Ask patients about recent food history, particularly shredded lettuce or salad consumption at Taco Bell locations in Indiana, Kentucky, Michigan, Ohio, and West Virginia.
• —Treat confirmed cases with TMP-SMX for seven to ten days in immunocompetent patients. Consider longer courses for immunocompromised patients.
• —Report confirmed cases to local and state health departments. Cyclosporiasis is nationally notifiable in 47 states, the District of Columbia, and New York City.

• —Case counts reflect confirmed laboratory-verified cases reported to CDC as of mid-July 2026. The actual outbreak size is likely substantially larger given underdiagnosis, underreporting, and the six-week lag for outbreak attribution.
• —The Taco Bell-linked cluster and the broader national surge are being investigated as separate but potentially related events. The full scope of produce sources contributing to the national case count has not been established.
• —This review is based on public health surveillance data and a government health alert notice, not a peer-reviewed clinical trial. That reflects the nature of a breaking outbreak, not a limitation of the underlying data.
• —The outbreak is actively evolving. Case counts, implicated food sources, and clinical guidance may be updated after this review is published. Readers should check the CDC sources linked below for the most current information.

There is a Cyclospora outbreak moving through the United States food supply right now. More than 1,645 confirmed cases across 34 states, with thousands more under investigation. The source, for the largest identified cluster, is shredded iceberg lettuce served at Taco Bell. The parasite is one of the most routinely missed organisms in clinical workups. The treatment works when the right test is ordered. If you are seeing patients this summer with prolonged watery diarrhea, Cyclospora belongs on your differential.