Clark County Public Health is continuing its investigation into a possible case of measles in a child, and has identified the Legacy Salmon Creek Medical Office Building as a fourth location where people may have been exposed to measles.People who visited the medical office, 2121 N.E. 139th St. in Vancouver, and used the lobbies, stairwells and elevators from 10:45 a.m. to 2 p.m. July 3 may have been exposed, according to a press release from Clark County Public Health.Three other businesses were also previously announced: J.C. Penney, 19005 S.E. Mill Plain Blvd., Vancouver (from 2 to 5 p.m. June 27); Ross Dress for Less, 4708 N.E. Thurston Way, Vancouver (noon to 3 p.m. June 28); and Svitoch, 4804 N.E. Thurston Way, Vancouver (noon to 3 p.m. June 28).Measles is spread through the air from coughs or sneezes, and it is contagious before symptoms emerge, which is up to three weeks after exposure.Symptoms begin with a fever, cough, runny nose and red eyes, followed by a rash that generally begins at the head and spreads. The contagious stage usually lasts four days before the rash appears, and up to four days after the rash’s appearance.