A measles outbreak spanning multiple states is nearing 600 cases, and experts say it might just be the beginning.

A day care facility in a Texas county that’s part of the measles outbreak has multiple cases, including children too young to be fully vaccinated, public health officials say.

Health officials said if anyone believes they’ve been exposed, they should quarantine for at least four days and contact their doctor.

Health officials are warning the public about a potential measles exposure on an Amtrak train to Washington, D.C. and at a health clinic in the city, and noted that those who have not yet been vaccinated are at risk for catching the virus.

In the state's second measles case of the year, a baby under 1 year old has been confirmed to have the virus. As babies cannot be vaccinated, they are highly vulnerable, health officials warn.