Officials at the U.S. Centers for Disease Control and Prevention have warned that the number of measles cases has reached a 20-year high, with 288 illnesses reported in the U.S. between Jan. 1 and May 23 of this year -- the most in the first five months of any year since 1994.
Sixty of the cases this year occurred in California, the CDC reported in its Morbidity and Mortality Weekly Report. Only in Ohio -- where an outbreak in Amish communities that traditionally eschew vaccination has sickened 138 people so far this year -- was there a higher incidence of the disease.
"Measles anywhere in the world can reach our communities and unvaccinated Americans are at risk," said Dr. Anne Schuchat, assistant surgeon general and director of the CDC's National Center for Immunizations and Respiratory Diseases, during a Thursday conference call with reporters. "This is not the kind of record we want to break."
Among the U.S. cases, Schuchat said, 90% occurred in people who were not vaccinated or whose vaccination status was unknown. Most unvaccinated people had decided against immunization for religious, philosophical or personal reasons, she added.
The California Department of Public Health, which tracks measles cases in the state, reports on its website that 13 counties have had measles cases this year. Orange County has had 22 cases -- more than twice as many as the next hardest hit county, Los Angeles, which reported 10.
In the April 25th edition of the CDC's Morbidity and Mortality Weekly Report, California researchers detailed characteristics of what was then 58 cases that had been reported in the state in 2014. Most were either unvaccinated or had no vaccination documentation available. People were sickened in healthcare facilities, households, a church daycare center, an airplane and a school, the team reported.
The median annual number of measles cases in California from 2000 to 2013 was nine, the team added, and ranged from 4 to 40 in a given year.
Measles was officially eliminated in the U.S. in 2000 -- meaning that the virus does not circulate here year-round, as it does in many other countries. But travelers who are not vaccinated and leave the country can bring the illness back with them from regions where it is more common, Schuchat said. Travel to and from the Philippines, where a large outbreak is ongoing, has been implicated in many of the cases in California and elsewhere in the U.S.
When infected travelers come in contact with unvaccinated people in the U.S., the highly contagious disease can spread.
"Our key message today is that we can stop this from being an even greater problem," Schuchat said, urging Americans to make sure they get vaccinated before the spring and summer travel seasons.