A Whatcom County woman, who has since been diagnosed with measles, traveled to several Western Washington locations, including Seattle and Tacoma, while she was contagious in late March, according to the Washington State Department of Health.

Measles is uncommon in Western Washington because most people have been vaccinated. However, for those who are not immune, the virus is highly contagious and, in rare cases, fatal.

People who aren’t immune can get the measles just by walking into where someone with the disease has been in the past few hours, public-health officials said. The woman, who is in her 20s, became contagious with measles March 26 after visiting a Whatcom County family member with measles linked to an outbreak in British Columbia, Health Department spokesman Donn Moyer said.

The woman visited Seattle for a Kings of Leon rock concert at KeyArena on March 28. That same day she was also at the Best Western Loyal Inn and the Wasabi Bistro, and the next day she went to Beth’s Cafe, Aurora Suzuki, Starbucks at First Avenue and Pike Street, and Pike Place Market.

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On those same dates she went to several Pierce County locations, including the LeMay Car Museum and Harmon Brewing Co. & Restaurant.

Anyone who was in those locations at the listed times and who is unvaccinated, who isn’t sure if he or she is immune or who develops an illness with fever or an unexplained rash should consult a health-care professional immediately.

People at the highest risk include those who are unvaccinated, pregnant women, infants younger than 6 months and people with weakened immune systems.

The woman’s diagnosis was traced to an outbreak of measles in the Fraser Valley, B.C., just north of the U.S.-Canada border. The majority of the cases in British Columbia are related to a private school that has a high number of unvaccinated children, according to a Whatcom County news release.

A case of measles in San Juan County has been confirmed, and health officials are working to contact anyone who may have been exposed. A traveler from California passed through Seattle-Tacoma International Airport on March 21 and 22 while contagious.

A typical case of measles begins with a mild to moderate fever, according to the U.S. Centers for Disease Control and Prevention, along with a cough, runny nose, red eyes and sore throat. The person may also have tiny white spots with blue-white centers inside his or her mouth. A red or reddish-brown rash appears three to five days after the start of symptoms.

Symptoms begin seven to 21 days after exposure.

A person with measles is contagious from about four days before the rash appears to four days after it appears.

There have been seven cases of measles confirmed in Washington this year. Washington typically has five or fewer measles cases per year, but that number fluctuates, Moyer said.

Paige Cornwell: 206-464-2530 or pcornwell@seattletimes.com