The Centers for Disease Control and Prevention reported 800 confirmed cases of measles in the U.S. as of Friday, making the announcement as the highly contagious illness has reached half of the country—though most cases remain focused in Texas.

The measles outbreak in West Texas now counts almost 600 cases, according to Texas health data released Friday. The 597 cases is 36 more than were tallied Tuesday, according to information from Texas Health and Human Services.

State health officials said fewer than 30 of the cases identified by the state were considered "actively infectious."