Complex sentence: In August 2014, Enterovirus D68 caused clusters of respiratory disease in 11, mostly Midwestern, states of the U.S., first confirmed in Kansas City, Missouri, and Chicago.
Split into simpler sentences: In August 2014, Enterovirus D68 caused clusters of respiratory disease in the United States. The outbreak began in 11, mostly Midwestern, states and was first confirmed in Kansas City, Missouri, and Chicago.