A measles outbreak in northwest Texas grew to 124 cases in nine counties on Tuesday, and health officials warned that residents in other parts of the state may have been exposed to the highly contagious respiratory illness.

The number of confirmed measles cases reported in an outbreak in West Texas is now at 124, the Texas Department of Health Services said in an update Tuesday, an increase of 34 since late last week.

The Hays County Health Department has issued an alert of a potential measles exposure in San Marcos. The San Antonio Metropolitan Health District has issued an alert of a potential measles exposure there.