CDC investigates multi-state Cyclospora outbreak as Michigan cases top 1,200

Public health officials are investigating a fast-moving multi-state outbreak of cyclosporiasis, a parasitic infection caused by Cyclospora cayetanensis, as Michigan reports the largest cluster and the source remains unknown.

Reporting published July 9 said Michigan had more than 1,200 reported cases and at least 40 hospitalizations. Other coverage described different case totals from earlier data cutoffs, underscoring how quickly the outbreak has been changing.

The broader investigation appears to reach well beyond Michigan. Reporting on July 9 said health officials were looking at cases in at least 16 other states, with investigations ongoing in 28 states overall.

What health officials know

CDC reference material describes cyclosporiasis as a foodborne and waterborne illness that commonly causes watery diarrhea and other gastrointestinal symptoms. The parasite is spread through contaminated food or water, not through direct person-to-person transmission.

The CDC also says U.S. outbreaks have been identified nearly every year since the mid-1990s, with cases most common in spring and summer. Past outbreaks have been linked to raw produce including cilantro, lettuce, basil and salad mixes.

The current outbreak has drawn attention because of both the scale of illness and the speed of the case growth. Separate reports said Michigan had climbed to nearly 1,000 cases in one update before later coverage put the state above 1,200.

Ohio has also reported a sizable cluster, with one report citing 177 cases. In a separate CDC update cited by reporters, the agency had confirmed 145 cases across 17 states.

Michigan is the largest reported cluster

Michigan appears to be the epicenter of the outbreak. State-level reporting has made it the largest known cluster by a wide margin, and the case count has continued to rise as local and federal officials compare notes.

Texas has also reported cases. The Houston Chronicle said Houston-area officials had identified more than 30 local cases, and that Texas had at least 48 cases meeting the CDC outbreak case definition between May 1 and July 6.

The source is still unknown

The main unanswered question is what contaminated food or water triggered the outbreak. Across the reporting, investigators had not identified a source or confirmed a specific food vehicle.

That leaves health officials in an active traceback phase. The immediate next steps are to keep updating case counts, identify linked exposures and determine whether a common supplier, product or distribution chain is involved.

For now, the outbreak remains a developing public-health event with a familiar seasonal pattern but an unresolved source. Officials are still tracking hospitalizations, geography and possible links between patients as the investigation continues.