Orange County now has 22 reported measles cases, a number that has nearly doubled in the last two weeks. There had been only three reported cases of measles in the previous five years. Statewide, the number of cases has grown to 51.
Though Orange County has only a slightly higher rate of parents who opt out of immunization requirements than the state average, there are pockets — particularly in the county's more affluent southern communities — where larger numbers of parents are choosing not to immunize their children, said Dr. Matt Zahn, medical director for epidemiology at the county Health Care Agency.
"We know that there is a vigorous anti-vaccine movement in this country," Zahn said. "So events like this are difficult, but they're important to highlight because we want to make sure people realize that there's reason that you need to get your child vaccinated."
In order to protect the larger community, health officials said it's possible that unimmunized children could be ordered to stay home for a couple of weeks if their school or day care reports a case of measles.
Five children in the county have been affected by measles and none were immunized. Five other cases occurred in healthcare workers who were treating measles patients, according to the agency.
Measles starts with fever, cough, runny nose and pink eye and is followed a few days later by a rash that begins on the face and upper neck and spreads down the body.
It is highly contagious but can be prevented with a measles,
According to state data for the 2012-13 school year, 3.03% of Orange County kindergartners enrolled in school with personal belief exemptions, which allow parents to opt out of immunizations. In Los Angeles County, where there have been 10 reported cases, it was 1.88%. Statewide the rate is 2.79%.
There are many counties with much higher opt-out rates. In Nevada County, 22.44% of kindergartners had exemptions, and in Calaveras County the rate was 10.64%. In Santa Barbara County, 4.27% opted out.
However, the overall county rate can be deceptive, Zahn said.
"If you look at reported outbreaks across the nation, it is very often not widespread throughout a county, but it is a focal event where one particular part of the community or even just one school is involved," he said.
"The outbreak that is going on in our community is weighted toward kids who have not been immunized," he said. "So get your children immunized."