The Texas health department reported 646 cases of measles in the state on Friday, an increase of 22 cases from three days ago, as the United States battles one of its worst outbreaks of the childhood disease.

State health officials on Friday said the number of measles cases in the state linked to a West Texas outbreak has grown to 646 since January.

The measles outbreak that began in West Texas now totals 725 cases across three states. Less than 10 cases in Texas are considered actively infectious.