Summary (tl;dr)

A parasite outbreak causing severe, sometimes explosive, diarrhea known as cyclosporiasis is currently affecting hundreds of people across at least 18 states in the United States, prompting ongoing investigations by health officials.

Essential Background

Cyclosporiasis is an intestinal illness caused by the microscopic parasite Cyclospora cayetanensis. People become infected by consuming food or water contaminated with the parasite, often linked to fresh produce. Direct person-to-person spread is uncommon. The Cyclospora season typically runs from May 1 through August 31, with cases historically rising during the spring and summer months.

The Full Story

The Centers for Disease Control and Prevention (CDC) is actively monitoring a multistate outbreak of cyclosporiasis, which has resulted in at least 145 domestically acquired cases across 17 states as of June 16, 2026. An additional 170 cases across seven counties, including a cluster in Monroe County, have been reported by the Michigan state health department, which are not yet included in the CDC's national count. These illnesses, characterized by symptoms like watery and explosive diarrhea, loss of appetite, and fatigue, began between May 1 and June 6, 2026. Twenty individuals have been hospitalized, but no deaths have been reported. Local, state, and federal health agencies are investigating several clusters of cases to identify the source of contamination, though there is currently no evidence of a single, widespread outbreak linking all reported cases.

Why It Matters

This ongoing outbreak highlights a significant public health concern, as cyclosporiasis can lead to prolonged gastrointestinal illness lasting weeks or even months if untreated, and symptoms can recur. While typically not life-threatening, the severity of symptoms, including explosive diarrhea, can be debilitating. The challenge in identifying a single source, coupled with the fact that routine sanitizers are ineffective against Cyclospora, underscores the importance of thorough washing of all fresh produce and adherence to food safety guidelines to prevent further infections.

Geographic Location

• United States (nationwide parasite outbreak)
• New York, United States (highest cluster of cases, 31-80 reported cases)
• Illinois, United States (11-30 reported cases)
• Texas, United States (11-30 reported cases)
• Monroe County, Michigan, United States (cluster of cases reported)
• Alaska, United States (1-10 reported cases)
• Colorado, United States (1-10 reported cases)
• Connecticut, United States (1-10 reported cases)
• Florida, United States (1-10 reported cases)
• Georgia, United States (1-10 reported cases)
• Louisiana, United States (1-10 reported cases)
• Massachusetts, United States (1-10 reported cases)
• New Jersey, United States (1-10 reported cases)
• North Carolina, United States (1-10 reported cases)
• Ohio, United States (1-10 reported cases)
• Pennsylvania, United States (1-10 reported cases)
• Tennessee, United States (1-10 reported cases)
• Virginia, United States (1-10 reported cases)
• Wisconsin, United States (1-10 reported cases)