Outbreak of diarrhea caused by parasite jumps to 3,000 cases. Here’s why it’s so hard to identify the source

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source . Michigan reported 2,640 cases as of 9:30 a.m. Monday, including 44 hospitalizations. Ohio has reported 361 cases since June 1. At least 46 people have been hospitalized. As of July 10, 31 states have reported cases to the US Centers for Disease Control and Prevention, although it’s not clear whether they’re all part of the same outbreak. The CDC says “multiple states” have reported an increase in cases in the last two weeks compared with the same period in 2025. The agency said Friday that its national count — 843 confirmed cases since May 1 — is lower than states’ counts while cases undergo further analysis. It’s not clear what is causing the surge in cases, and it’s difficult for investigators to pin it down. Cyclosporiasis cases are slow to be counted; genomic testing for cases is complicated; and some public health systems that track foodborne illness have recently faced...