Health officials are unsure how a 49-year-old Whatcom County woman contracted measles this month.
The woman, who has the first case of measles in Whatcom County since 1995, told officials she had not traveled out of the area and had not knowingly come in contact with anyone from outside the U.S.
The woman is not seriously ill and was never hospitalized, said Whatcom County Health Officer Greg Stern.
Widespread immunization beginning in the 1960s all but eliminated the disease in the U.S., and the disease is now generally limited to sporadic outbreaks involving contact with international residents, Stern said.
"This is unusual in that we don't have a clear source of infection," Sterns said of the woman's case.
The woman told officials she had not had measles in the past and did not believe she'd been vaccinated for the disease.
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