At least 58 cases have been confirmed. Health officials — who are scrambling to get a handle on the vaccine-preventable outbreak — suspect 200 to 300 people may be infected.

The U.S. declared measles eliminated in 2000 "thanks to a very high percentage of people receiving the safe and effective measles, mumps, and rubella vaccine," the CDC said, but now U.S. coverage among children of kindergarten age is below the 95 percent coverage target, which creates a higher risk for outbreaks of the virus.