People across the United States are taking a closer look at their lettuce and leafy greens this summer because of an outbreak of cyclosporiasis, a gastrointestinal illness whose most notable symptom is severe, watery diarrhea.

It took weeks for the CDC to issue a health advisory over the growing number of cyclosporiasis cases.

A recent outbreak of cyclosporiasis—a foodborne illness contracted from eating contaminated food, typically fresh produce—has impacted at least 34 states nationwide.