Health officials in Washington state have now confirmed 23 cases of measles in Clark County, with an additional two more suspected. The county health department said 20 of the confirmed cases, which were mostly found in children ages 1 to 4, involve patients who were not immunized, while the vaccination status of the other three individuals had not been verified.

In an update posted to Clark County’s website on Tuesday, officials said 18 cases were confirmed in patients ages 1 to 10, while four occurred in patients ages 11 to 18, and one was confirmed in a patient between 19 and 29.

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The measles virus is a highly contagious illness that may present with a high fever, cough, runny nose, red, watery eyes, white spots inside the mouth, and rash. According to the Centers for Disease Control and Prevention (CDC), the virus is so contagious that if one person has it, 90 percent of the people close to that patient who have not received immunization will also become infected. It can be serious, particularly in children younger than 5 and in adults older than 20. Complications can result in permanent hearing loss, pneumonia and encephalitis.

Transmission can be prevented with the MMR vaccine, which in addition to measles also protects against mumps and rubella, and by avoiding exposure. The CDC recommends children get two doses of the vaccine.

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“Clark County Public Health is urging anyone who has been exposed and believes they have symptoms of measles to call their health care provider prior to visiting the medical office to make a plan that avoids exposing others in the waiting room,” the post said. “People who believe they have symptoms of measles should not go directly to medical offices, urgent care centers or emergency departments (unless experiencing a medical emergency) without calling in advance.”

Several health care facilities were listed as places of possible exposure locations with times dating back to Dec. 31 and as recently as Jan. 19. Twelve schools were also included as potential exposure sites, with the county requiring “exclusion of students and staff without documented immunity to measles” from those locations. Three churches, several retail stores and the Moda Center, where the Trail Blazers play, were also identified.

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“Public Health has established a call center for questions related to the investigation. Anyone who has questions about public exposure should call, 360-397-8021,” the post said.