Fraser Health says it traced a BCIT student's measles infection to an outbreak that showed up this month clustered around Chilliwack's Mount Cheam Christian School.
The outbreak has now spread into the general population in Fraser Valley East, and so far 100 suspected cases have been reported in Chilliwack and Agassiz.
Health officials say the only way to curb the current outbreak is isolation and vaccination.
Who should seek out the measles, mumps and rubella (MMR) vaccine?
Vancouver Coastal Health's Dr. John Carsley says any adult born before 1970 is thought to be immune because they either had it or were exposed to it when they were younger.
But anyone born after 1970 should have been vaccinated against measles — twice.
"If people have least suspicion they may not have had two measles vaccines, they should get one right away," he said.
What if you aren't aware of your immunization history?
Dr. Meena Dawar, also with Vancouver Coastal Health, says to check with the records on file with your family doctor, if you have one, and, if in doubt, get vaccinated again.
"There's no harm in getting another dose of measles-containing vaccine, so go ahead and get another dose of MMR," she told CBC Radio One's On The Coast Monday afternoon.
But, she added, there is one major exception to the rule, and that is pregnancy.
"The vaccine is contraindicated in pregnant women, because it is a weakened form of the measles virus," she said.
A blood test can be done to check a pregnant woman's immunity, Dawar said, and if she is found to be at risk, an immunoglobulins can be administered to offer her full protection.
Why is there an outbreak?
Though once virtually eradicated in Canada, measles has been making a comeback. Travellers returning from out of the country seems to be one entry point, Dawar says.
Carsley said one of the reasons measles spreads so easily is that the tell-tale red rash doesn't appear until three or four days after a person comes down with other symptoms, including a fever and a cough, and the person may be infectious even before then.
"You can spread the disease before you have any symptoms at all, that is why it is so difficult to control other than by vaccination," he said.
Measles spreads by touch or through the air when an infected person breathes, coughs or sneezes.
Vancouver Coastal Health says the complications of measles can be serious, including respiratory problems and pneumonia.
Health officials are asking anyone with symptoms to isolate themselves at home and call ahead to their doctor, health unit, or hospital if their symptoms become severe enough to need medical attention.
What are the symptoms of measles?
Symptoms of measles may develop seven to 21 days after exposure to an infected person.
Symptoms include a high fever, cough, runny nose, cough, drowsiness, irritability, and red and inflamed eyes. Small white spots may appear in the mouth and throat.
A red blotchy rash begins to appear on the face three to seven days after the start of symptoms, then spreads down the body to the arms and legs. This rash usually lasts four to seven days.
Symptoms generally last from one to two weeks.