(Reuters) -The Texas health department reported 683 cases of measles in the state on Friday, an increase of 20 cases since April 29, as the U.S. battles one of its worst outbreaks of the childhood disease.

There have been four measles cases reported in the Dallas-Fort Worth area this year: one in Collin County, one in Denton County and two in Rockwall County. State authorities have not officially tied any of those cases to the outbreak that began in Gaines County, and all four appear in the state public health department’s list of “other 2025″ cases.

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.