The largest cluster of cases tied back to Taylor Farms lettuce now accounts for cases in 15 states.

The outbreak is linked to lettuce served at Taco Bell and sold in grocery stores, but it’s unlikely all of the cyclosporiasis cases were caused by a single item.

The diarrhea-inducing parasite, linked to shredded iceberg lettuce from mega produce supplier Taylor Farms, has been making thousands of people sick this summer