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.

State medical experts have confirmed 124 cases of measles in Texas. This is the largest measles outbreak in Texas in 30 years. Here is how it started and an overview of the situation, as of Feb. 25.