The number of confirmed cases in Clark County’s measles outbreak grew to 21 on Sunday, with another four suspected cases and four new exposure sites — including Evergreen High School.Clark County Public Health reported that 16 of the cases involved children ages 1 to 10, with four cases in youths ages 11 to 18 and case in an adult between the age of 19 and 29. Of those cases, 18 patients had not been immunized, and immunization of three others has not been verified. One person has been hospitalized.Clark County declared a public health emergency Friday over the growing measles outbreak following news that a person contagious with measles attended a Jan. 11 Portland Trail Blazers game at the Moda Center. That game was nearly sold out, with 19,393 people attending, according to ESPN.On Sunday, health officials added the following exposure sites and times to their list:Evergreen High School, 14300 N.E. 18th St., Vancouver on Wednesday, Jan. 9.Vancouver Clinic Columbia Tech Center, 501 S.E. 172nd Ave., Vancouver from 11:30 a.m. to 4 p.m. Friday, Jan. 11.Slavic Christian Academy, 7300 MacArthur Blvd., Vancouver on Monday, Jan. 7.GracePoint Christian Church, 7300 MacArthur Blvd., Vancouver from 6:30 a.m. to 5:30 p.m. Monday, Jan. 7.Evergreen High School had an enrollment of more than 1,700 students as of October, according to state records.Clark County Public Health is requiring exclusion of students and staff without documented immunity to measles from only schools identified as possible exposure sites. Students and staff excluded from those identified schools are also excluded from other schools, child care and other congregate settings.Students and staff at schools where measles exposure did not occur are not impacted by exclusions.The Centers for Disease Control and Prevention reports that 90 percent of unvaccinated people exposed to the measles virus develop the disease. The virus lives in the nose and throat mucus of an infected person, and can survive for up to two hours in an airspace where the infected person coughed or sneezed.