The measles outbreak first reported in Gaines County, Texas, has doubled to 48 cases in the last four days, the Texas Department of State Health Services said in a statement Friday.

The measles outbreak in the South Plains region, in West Texas, has expanded to at least 48 people, most of them children.

In the last three weeks, 48 cases of measles have been identified, sending 13 patients to the hospital, according to the Texas Department of State Health Services.