The Texas health department reported 259 measles cases in the state on Friday, an increase of 36 cases from its previous count on March 11, as one of the largest outbreaks the U.S. has seen in the last decade spreads.

Half of the newly reported cases are in Gaines County, about 80 miles southwest of Lubbock, which has been the epicenter of the outbreak. The Texas Department of State Health Services has confirmed 259 cases of measles since late January.