PORTLAND, Ore. (AP) — Health officials in northwestern Oregon say a third person has tested positive for measles.

Multnomah County health officials tell KATU-TV that the person, who was not vaccinated, tested positive Friday.

Officials say the person had close contact with another person diagnosed with measles on July 6.

Health officials say that about 500 people have been exposed to a confirmed case of measles in the Portland area.

Officials say those with the highest risk of catching measles are those who aren't vaccinated, pregnant women, infants under 12 months old and people with weakened immune systems.

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Information from: KATU-TV, http://www.katu.com/