SEATTLE — An airline passenger who was contagious with measles passed through Seattle-Tacoma International Airport on March 26, possibly exposing others to the disease.

The passenger flew on Northwest Airlines flight 33 from Amsterdam to Seattle, where she switched to Horizon Airlines Flight 2243 to Portland. The woman, who is in her 20s, developed a rash two days later, on March 28.

Measles is contagious from about four days before the rash appears and for four days afterward. The woman left Portland for Amsterdam on March 29 aboard Northwest Flight 92.

When someone who is infected with measles sneezes or coughs, he or she can spread the virus through the air and infect others.

King County public-health officials are contacting three King County residents who were seated close to the woman on the Seattle flight. They advise that passengers aboard Flight 33 or anyone who was in the S and C concourses and the S concourse train on March 26 between 3:25 p.m. and 7 p.m. contact a doctor if they become ill.

Measles symptoms appear a week to 21 days after exposure and include fever, rash, cough and red, watery eyes.