The CDC expanded the outbreak of cyclosporiasis linked to shredded iceberg lettuce to an additional four states, a CDC official told ABC News on Friday.

Some US states are facing a large and growing outbreak of diarrhea caused by cyclospora, a microscopic parasite that can contaminate fresh food or water.

CDC confirms 4,173 U.S. Cyclospora cases as it investigates a lettuce-linked outbreak. More than 7,400 additional reports remain under review.

Investigators believe additional states will help them better construct how cyclosporiasis moved through the nation's food supply.