The four newly linked states – Illinois, Kansas, Oklahoma and Pennsylvania – join Indiana, Kentucky, Ohio, West Virginia and hard-hit Michigan.

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.