There are more than 930 confirmed cases of measles across the U.S. as of Friday, according to the Centers for Disease Control and Prevention, with a majority of the highly contagious illness present in Texas.

The measles outbreak centered in northwest Texas grew to 683 cases and spread to three new counties on Friday, according to health officials. The latest update from the Texas Department of State Health Services adds 20 new cases since the agency's last update on Tuesday.