Public health officials say they're investigating a "cluster of measles" at a suburban daycare center.
Two children at a KinderCare Learning Center in Palatine have been confirmed to have the virus while test results for three others are pending, though they have been diagnosed by clinical and epidemiological criteria, officials said.
Another 10 children are at-risk of contracting measles, said Dr. Terry Mason, the CEO of the Cook County Department of Public Health. A majority of those who may have been exposed are too young for a vaccination, Mason said.
Officials expect even more cases to be diagnosed.
Here are a few things you should know about measles.
What is measles?
Measles is a highly contagious respiratory disease that causes fever, red and sore eyes, runny nose, cough and a characteristic rash. The disease can cause severe health complications, including pneumonia, encephalitis and death.
How is it spread?
Measles is transmitted by contact with an infected person through coughing or sneezing and can remain in the air and on surfaces for up to two hours. Infected people are contagious from four days before their rash starts through four days afterwards.
How can you prevent it?
The Illinois Department of Public Health and the Cook County Department of Public Health say vaccinations are the safest, most effective way to protect individuals from measles and other potentially dangerous communicable diseases. Children who are under the age of one or with certain clinical conditions cannot be vaccinated and are therefore at highest risk for measles.
"Residents are strongly encouraged to get vaccinated to protect themselves and the most vulnerable members of the community," IDPH said in a statement.
The Centers for Disease Control and Prevention said one dose of measles vaccine is about 93 percent effective at preventing measles if exposed to the virus, and two doses is about 97 percent effective.
How many people are affected?
There has been at least one other confirmed case of measles in suburban Cook County in 2015, according to the Cook County Department of Public Health.
The CDC said 102 cases were reported in the U.S. in January alone. States affected include Arizona, California, Colorado, Illinois, Minnesota, Michigan, Nebraska, New York, Oregon, Pennsylvania, South Dakota, Texas, Utah and Washington. An outbreak at Disneyland was said to be responsible for 92 percent of those reported cases.
Is measles widespread?
Each year there are 20 million cases around the world, and 145,000 people die, according to the CDC.
Last year, the United States experienced a record number of measles cases, with 23 outbreaks reported, including one large outbreak of 383 cases occurring primarily among unvaccinated Amish communities in Ohio, the CDC said.
Many of the cases in the U.S. in 2014 were associated with cases brought in from the Philippines, which experienced a large measles outbreak.
Hasn’t measles been eliminated in the U.S.?
In 2000, the United States declared measles was eliminated, meaning it is no longer native to the country. Health officials say, however, that unvaccinated travelers who get measles in other countries can bring it back into the U.S.
Since 2000, the annual number of people reported to have measles ranged from a low of 37 people in 2004 to a high of 644 people in 2014, according to the CDC.
Before the measles vaccination program started in 1963, health officials estimate that about 3 to 4 million people got measles each year in the United States. Of those people, 400 to 500 died, 48,000 were hospitalized, and 4,000 developed encephalitis (brain swelling) from measles.
Is there cause for concern?
It is possible that measles could become endemic in the U.S. again, particularly if vaccine coverage levels drop, according to the CDC.