Seventeen people in Los Angeles County have contracted the bacterial food-borne illness listeriosis, including two pregnant women who had stillbirths, health officials said Tuesday.

The number of cases — tracked between August and November — is nearly double the number reported during the same period last year, officials said.

The increase in cases does not constitute an outbreak, however, because they were not linked to a common source, said Dr. Jonathan Fielding, the county's director of public health.

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