Cyclospora cayetanensis clusters exceed seasonal norms in 12 states since May 2026

State and territorial health departments notified the CDC of 248 confirmed cases meeting the national case definition, with symptom onset clustered between May 15 and July 3. Whole-genome sequencing of 87 isolates showed three dominant clades, two of which matched prior outbreaks traced to fresh cilantro and basil imported from Mexico. Hospitalization occurred in 19 percent of cases; no deaths were reported. Traceback investigations point to two distribution networks serving restaurants and grocery chains in the Northeast and Midwest.

Seasonal Cyclospora transmission in the United States is almost entirely foodborne and tied to imported produce. The current elevation coincides with expanded summer imports of leafy greens and herbs following weather-related harvest shortfalls in domestic growing regions. Unlike bacterial pathogens, Cyclospora oocysts require days to weeks of environmental maturation, complicating real-time testing of incoming shipments. Routine produce screening remains limited to targeted lots after illnesses are detected.

Prior large outbreaks (2013, 2018, 2023) demonstrated that once contaminated lots reach retail, case counts continue for four to six weeks even after product withdrawal. The current genomic diversity suggests at least two independent contamination events rather than a single point source. Enhanced import sampling and irradiation pilots have reduced risk in targeted commodities but have not been scaled to all high-risk herbs.

CDC will release updated case counts weekly through September and coordinate with FDA on expanded traceback of remaining lots. States are urged to expedite stool oocyst testing in patients with prolonged watery diarrhea. Next-season prevention hinges on whether FDA implements mandatory lot-level testing for cilantro and basil entering from endemic production areas.