WASHINGTON (Reuters) - The biggest U.S. outbreak of measles since 1997 has sickened 127 people in 15 states, most of whom were not vaccinated against the highly contagious viral illness, federal health officials said on Wednesday.
The outbreak was driven by travelers who became infected overseas -- 10 countries are implicated -- then returned to the United States ill and infected others, according to the U.S. Centers for Disease Control and Prevention.
Thanks to a vaccination program dating to 1963, measles is no longer endemic in the United States, with ongoing transmission of the virus declared eliminated in 2000.
Public health officials have been stressing the importance of immunizing children amid increasingly vocal vaccine opponents who object to them for religious or other reasons or because they fear the shots may cause autism or other harm.
British health officials said last month that measles had again become endemic in that country for the first time since the mid-1990s due to parents declining to get their children vaccinated.
"The primary reason for lack of vaccination is personal belief exemptions," the CDC's Dr. Larry Pickering told a news conference arranged by the National Foundation for Infectious Diseases.
"Until better global control is achieved, cases will continue to be imported into the United States and outbreaks will persist as long as there are communities of unvaccinated people," Pickering said.
The CDC first gave details about the current outbreak in May when there were 72 people sick in 10 states. At that time, it was the most cases since 116 in 2001.
With the total number of sick people now at 127, this is the most since 138 people in 1997 and 508 in 1996, the CDC said.
The last serious U.S. outbreak occurred from 1989 to 1991, when 55,000 people got measles and 123 died.
No deaths have been reported in the current outbreak.
States with cases, the CDC said, include Arizona, Arkansas, California, Georgia, Hawaii, Illinois, Louisiana, Michigan, Missouri, New York, New Mexico, Pennsylvania, Virginia, Wisconsin and Washington state, as well as Washington, D.C.
Travelers got measles in Switzerland, Israel, Belgium, Italy, India, Germany, China, Pakistan, Russia and the Philippines, the CDC said.
Measles remains a leading cause of death among children in poor countries, killing about 250,000 people a year globally.
The disease causes fever, cough, redness and irritation of the eyes and a rash. Serious complications include encephalitis and pneumonia that can be fatal.
Editing by Julie Steenhuysen and Peter Cooney