Summary (tl;dr)

A significant outbreak of cyclosporiasis, a parasitic intestinal illness causing severe and often explosive diarrhea, is currently surging across the United States, with thousands of cases reported, primarily impacting Michigan and Ohio.

Essential Background

Cyclosporiasis is an intestinal illness caused by the microscopic parasite Cyclospora cayetanensis. It is typically transmitted when people consume food or water contaminated with feces containing the parasite. Unlike some other illnesses, it is not generally spread directly from person to person. Outbreaks are seasonal in the U.S., usually peaking during the spring and summer months (May through August), as the parasite thrives in warm, humid conditions and there's increased consumption of fresh produce. Historically, outbreaks have been linked to various types of fresh produce, such as basil, cilantro, raspberries, lettuce, and snow peas.

The Full Story

Since May 2026, thousands of cyclosporiasis cases have been reported across more than 30 U.S. states, with particularly large clusters in Michigan and Ohio. Michigan alone has documented over 1,200 cases, making it the largest outbreak in the state's history and one of the nation's biggest in recent years. Ohio has also seen a sharp increase, with over 500 cases reported in northwestern Ohio, and 177 cases statewide as of early July. Other states, including New York, Illinois, Massachusetts, Pennsylvania, and Maryland, have also reported significant numbers of illnesses.

Health officials, including the CDC and FDA, are actively investigating the surge; however, a single, specific contaminated food source linking all cases has not yet been identified. Despite CDC reports of 145 cases across 17 states between May 1 and June 16, 2026, state-level reporting indicates the actual number of illnesses is substantially higher, as many people may recover without medical care or testing.

Why It Matters

This widespread outbreak is causing significant concern due to the severity and duration of cyclosporiasis symptoms, which can include profuse, watery, and often explosive diarrhea, abdominal cramps, bloating, nausea, and fatigue that can last for weeks or even months if untreated. While rarely fatal, the illness can lead to dehydration and may require hospitalization, particularly for vulnerable populations like young children, the elderly, and those with weakened immune systems. The unidentified common source makes it challenging for the public to take specific preventive measures beyond general food safety guidelines, amplifying worries about contaminated fresh produce during peak summer consumption. The fact that Cyclospora surveillance became optional for some states as of July 2025 also raises questions about the accuracy and comprehensiveness of national tracking data.

Geographic Location

• Michigan, United States (widespread parasitic illness outbreak, over 1,200 cases reported, largest in state history)
  • Monroe County, Michigan, United States (high reported case counts)
  • Lenawee County, Michigan, United States (high reported case counts)
  • Washtenaw County, Michigan, United States (high reported case counts)
  • Wayne County, Michigan, United States (high reported case counts)
  • Shiawassee County, Michigan, United States (high reported case counts)
  • Jackson County, Michigan, United States (high reported case counts)
  • Oakland County, Michigan, United States (high reported case counts)
  • Livingston County, Michigan, United States (high reported case counts)
• Ohio, United States (widespread parasitic illness outbreak, over 500 cases in northwestern Ohio, 177 statewide by July 2)
  • Lucas County, Ohio, United States (306 confirmed cases)
  • Wood County, Ohio, United States (increased confirmed cases)
  • Wyandot County, Ohio, United States (increased confirmed cases)
  • Ottawa County, Ohio, United States (10 reported cases)
  • Huron County, Ohio, United States (1 reported case)
  • Jackson County, Ohio, United States (2 reported cases)
• New York, United States (over 100 cases since May, significant increase compared to prior year in NYC)
• Illinois, United States (141 reported cases)
• Massachusetts, United States (18 cases reported since May)
• Pennsylvania, United States (28 cases in 2026, 14 in Southeastern Pennsylvania)
• Maryland, United States (32 confirmed cases in 2026, 28 since May 1, including at least one in Baltimore)