Public health officials say a contagious traveler with measles passed through Seattle-Tacoma International Airport on Thursday.
Measles is a highly contagious virus but most people in Washington are immune because they have been vaccinated.
The disease is mainly spread through the air when a person with measles coughs or sneezes.
People at highest risk from exposure are the unvaccinated, pregnant women, infants under six months of age and those with weakened immune systems.
The contagious traveler flew from Beijing to Seattle on July 4.
The Centers for Disease Control and Prevention is contacting people who were on the same flights as the contagious traveler.