As of April 25, there were 64 reported cases of measles nationwide this year, including 12 in San Diego.
There were about 30 cases of measles in all of 2007.
Before the advent of federally funded vaccine programs in the last decade, outbreaks spread quickly among low-income children who lacked access to vaccinations.
"Now, I think we're seeing a different trend with communities or pockets of under-immunized children" that are more linked to vaccine exemptions, Schuchat said.
Measles is a highly contagious disease that can cause a rash, high fever, cough, runny nose and red watery eyes. It also can cause diarrhea, ear infections, pneumonia, brain injury, seizures and death.
Before the measles vaccine was introduced in 1963, there were up to 4 million reported cases and up to 500 deaths each year in the United States. But vaccination programs were so successful that public health officials declared widespread transmission of the disease eliminated in 2000.
The recent outbreak that infected a dozen children in San Diego underscores the concern of public health officials.
An unvaccinated 7-year-old boy who visited Switzerland brought the disease to his school in January.
Nearly 10% of the students at the San Diego Cooperative Charter School had received personal-belief exemptions from vaccinations.
The boy infected five children at his school, four at his doctor's office and his two siblings. All were unvaccinated.
A separate outbreak, centered in Tucson, spread after an adult visitor from Switzerland in February was hospitalized for measles and pneumonia.
As of Thursday, there have been at least 17 confirmed cases, and all had no records of vaccination. The outbreak is ongoing.
Measles cases are on the rise in New York City, with 22 cases reported in Brooklyn. Health officials have linked those cases to outbreaks in Europe and Israel.
Switzerland, for example, is facing its most severe outbreak in the last decade; 2,000 people have fallen ill in the last two years. The disease has spread especially rapidly in communities that believe in alternative medicine and avoid vaccination.
In Israel, 1,000 people have fallen ill since August in an outbreak that started among nonimmunized ultra-orthodox communities in Jerusalem.
In Los Angeles County, officials reported one measles case in April in which a preschool-aged child was hospitalized.
U.S. health officials are concerned about small but increasing numbers of parents who are choosing not to vaccinate their children.