The number of confirmed Disneyland-related measles cases in California has increased to 29, according to local and state health officials. All but three of those cases are among people living in Southern California. That brings the overall tally to at least 33, counting the four confirmed cases among people from other states.
Most of the cases were contracted at Disneyland or California Adventure between Dec. 17 and Dec. 20, according to the California Department of Public Health. That's a narrower window of exposure; the Department initially said those who were infected were at the parks between Dec. 15-20.
Among those who are from out of state, two are from Utah, one is from Colorado and one is from Washington.
State health officials believe a foreign tourist introduced the measles to the theme parks. The disease was declared eliminated from the U.S. in 2000.
"What is unusual about this outbreak is the apparent infectiousness of the infected person (or persons)," state epidemiologist Gil Chavez says in an e-mail.
One person with measles can typically infect 12 to 18 people in an unvaccinated population, he says. The number of cases so far suggests "a very high rate of transmission, particularly in a population where most people are immune,” Chavez adds.
The state health department says the incubation period – the window of time between exposure and symptoms - for people who were exposed to the disease at the theme parks between Dec. 17-20 ended Jan. 10.
Any new cases will likely occur when people infected at Disneyland pass it on to someone in the community. That’s what happened with Orange County’s 10th case, announced on Wednesday. An unvaccinated teenager who had not visited the parks came down with the measles.
There is at least one other confirmed secondary case so far.
At least 16 of those who have gotten sick were unvaccinated, health officials say.
Measles typically starts with a high fever, cough, runny nose, and red watery eyes, followed a few days later by the telltale red rash that can spread throughout the body.