The warning was prompted by the potential exposure of thousands of people to the measles virus carried by a New Zealand teenager who visited Southern California from August 11 to 15 while sick with the disease.
A teenager who travelled from New Zealand to Southern California this month was infectious with highly contagious measles and may have exposed others at Disneyland and a nearby hotel, USA health officials say.
The Health Care Agency "has been working with the facilities listed above to reach people who had known close contact with this case", according to OCHCA.
According to the health agencies in Los Angeles and Orange counties, the teen visited Disneyland on August 12 and Universal on August 14.
The girl arrived at Los Angeles Global Airport on August 11 and went to the Barren role Palms Resort in Anaheim, officials acknowledged.
The Orange County health agency said people who may have been exposed should monitor themselves for symptoms such as fever and rash occurring up to 21 days from exposure.
"Measles is spread by air and by direct contact even before you know have it", said Dr. Muntu Davis, Los Angeles County's health officer.
She acknowledged she expects to glimpse extra measles cases, on the final, amongst worldwide travelers who talk about with California thanks to an develop in the illness foreign.
Anyone who develops the symptoms, especially those who haven't been vaccinated against measles or aren't sure they have, should stay home and call a doctor to schedule a visit, health officials said.
Review their vaccination history if they have not previously had measles.
Measles is one of the most contagious viruses in the world.
New Zealand - and the United States - are dealing with their worst outbreaks in decades.
A Tustin woman in her 50s was diagnosed last week with West Nile virus fever, becoming the first person to contract the virus in Orange County this year, officials said.
Dr. Pamela Hymel, chief medical officer of Disney Parks, Experiences and Products, said in a statement that park officials "have been advised by OC Health Care Agency that the risk to cast and guests is likely low".
Disneyland and adjoining Disney California Journey Park are main vacationer locations, drawing tens of 1000's of holiday makers a day.
Measles is a highly contagious disease, according to the US Centers for Disease Control and Prevention.