CDC Tracks Mystery Cyclospora Parasite Across 17 States as Summer Outbreak Season Peaks

Federal health officials are racing to identify the source of a microscopic parasite that has sickened at least 145 Americans across 17 states, with all confirmed cases linked to domestic infections as of mid-June 2026. The Centers for Disease Control and Prevention, the Food and Drug Administration, and state health agencies are jointly investigating multiple multi-state clusters, though no single unifying source has yet been identified.

Scope of the Outbreak

New York is the hardest-hit state, reporting between 31 and 80 confirmed cases, followed by Texas and Illinois, which have each recorded between 11 and 30 cases. The outbreak spans a wide geographic band — from Texas to Alaska — underscoring the difficulty investigators face in tracing a single point of origin.

Of the 145 confirmed patients, 20 have required hospitalization. No deaths have been reported. The patient population ranges in age from 5 to 86 years old, with a median age of 42. Women account for 61% of reported cases.

The Pathogen and Its Symptoms

The illness, cyclosporiasis, is caused by Cyclospora, a microscopic parasite. Its hallmark symptom is watery, often described as "explosive," diarrhea that can persist for weeks or even months without medical intervention. Accompanying symptoms include severe abdominal cramping, bloating, nausea, fatigue, and significant weight loss.

The infection can resolve on its own in some cases, but frequently requires antibiotics. The CDC advises anyone experiencing these symptoms to contact a healthcare provider promptly for testing and treatment.

A Predictable Season, an Unpredictable Source

The Cyclospora outbreak season runs officially from May 1 through August 31, a window during which warmer temperatures historically drive a spike in infections. The timing of this year's cluster aligns with that pattern, but the cause remains elusive.

The CDC has been careful to note the limits of what investigators know: "There is currently no evidence of a single, multistate Cyclospora outbreak linking all cases," the agency stated in its surveillance report. That distinction matters — it means health officials cannot yet point to a contaminated food supply or water source responsible for the full spread, leaving the investigation open across multiple simultaneous clusters.