The number of confirmed cases linked to the Disneyland measles outbreak continues to rise, with 62 confirmed cases in California alone; and the disease spreading to other states.
The outbreak began in early December, when authorities suspect that somebody who probably caught measles abroad visited one of the Disney theme parks in California and perhaps sneezed. That's all it might have taken, particularly since the once-common disease has become so rare that most Americans don't bother to get themselves vaccinated against it any more.
''Measles is so contagious,'' the Centers for Disease Control and Prevention said in a statement, ''that if one person has it, 90 per cent of the people close to that person who are not immune will also become infected.''
Now the measles that started at Disney has put California's Orange County, a hotbed of the anti-immunization movement, at the centre of the worst measles outbreak in the state in 15 years, with 62 confirmed cases statewide since December, according to the Los Angeles Times.
Additional cases that originated in California have spread to four other states and Mexico. The total infected is up to 70, including the five Disney employees who have since returned to work. About a quarter of those who got sick had to be hospitalised.
The outbreak in California is so alarming that, on Wednesday, state officials warned children under 12 and anyone not vaccinated or otherwise immune to measles to avoid the Disney parks. Disney resort employees who had contact with measles-stricken co-workers were asked to stay home unless they can show they've been vaccinated or prove through a blood test that they're immune.
The illness has since spread from the parks to 11 counties in California - and to Utah, Washington state, Colorado, Oregon and Mexico, according to official data. The greatest concentration by far, at least 20 cases, is in Orange County, which includes Disneyland and the Disney California Adventure Park, both in Anaheim.
That county has been at the centre of a nationwide movement against immunizations based in part on an erroneous belief - and a discredited study - linking vaccines to autism.
While California requires children to get shots to protect against measles, mumps and rubella (MMR,) parents who believe - despite the evidence - in links between the vaccines and medical conditions such as autism can get an exemption by signing a ''personal belief waiver,'' according to the Orange County Register.
According to state data, about 3 per cent of Orange County kindergartners have ''personal belief exemptions'' secured by their parents enabling them to opt out of immunizations.
One in three Americans, according to one recent poll, believe in a link between vaccines and autism, despite the absence of evidence.
''Measles is an infectious viral disease that resides in the mucus in the nose and throat of infected people,'' according to the CDC. ''When they sneeze or cough, droplets spray into the air and the droplets remain active and contagious on infected surfaces for up to 2 hours.''
This means anyone sneezed on who is not immune has a strong chance of getting the disease, characterized by fever, cough, runny nose, conjunctivitis and a rash that starts on the face and spreads across the body.
After someone is exposed who is not immune, it takes an average of 10 to 12 days before symptoms appear. The rash usually shows up after about 14 days, but the carrier can transmit the virus for about four days before the rash becomes visible.
For most people, measles is simply an annoyance - ''unpleasant,'' in the words of the CDC. But the complications can be dangerous and may include ear infections, diarrhoea and pneumonia. According to the CDC, one in 1,000 people with measles will develop inflammation of the brain, and ''one or two will die from it.''
Schools in Orange County are affected as well. After a student with measles showed up in the Huntington Beach Union school district, Orange County health officials ordered non-immune and unvaccinated students out of classes. As a result of the order, KPCC TV reported, 24 students were sent home.
''It is at large in the community now, and particularly infants too young to be immunized, people with other health conditions and, of course, people who aren't immunized need to be very concerned,'' Deanne Thompson, spokesman for the Orange County Health Care Agency, told the Orange County Register. ''They really should rethink that and consider getting vaccinated.''
The only potential good that might come out of the outbreak, wrote LA Times columnist Michael Hiltzik on Wednesday, is ''a much-needed jolt of reality'' to the ''dolts'' who shun vaccinations and officials who grant them exemptions from immunization laws.