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.

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

Cyclospora cases are rising across the US. Here's what to know about symptoms, spread, treatment and prevention.