Bay Area’s first Zika case diagnosed in Napa County

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A pregnant Napa County woman who had traveled to Central America has tested positive for the Zika virus in the Bay Area’s first case of the mosquito-borne disease, health officials said.

The woman, whom Napa County officials declined to identify, is no longer showing signs of Zika infection, which has been spreading primarily throughout Latin America and the Caribbean, health officials said. The woman had traveled to Central America within the past three months, the officials said.

The virus is believed to be linked in Brazil to thousands of cases of infants being born with abnormally small heads, a condition known as microcephaly. The World Health Organization has declared the epidemic a global emergency.

Napa health officials confirmed that the Bay Area case was acquired during the woman’s travel rather than from a bite from a local mosquito.

“This Zika virus case is not a threat to public health. There is no active transmission of Zika virus in Napa County, and the two kinds of mosquitoes that transmit the virus have not been found here,” Dr. Karen Relucio, Napa County health officer, said in a statement.

So far, all Zika infections diagnosed in the United States have involved people who traveled to regions affected by the outbreak. But the potential serious health impact on newborns as well the fact the disease can be transmitted sexually has heightened concerns.

The U.S. Centers for Disease Control and Prevention said last week that nine pregnant U.S. travelers have been diagnosed with Zika.

One woman gave birth to a baby with microcephaly.

California public health officials know of six state residents who have tested positive for the virus, including one from Yolo County.

Napa County health officials said pregnant women and those with sexual partners who travel to countries where Zika is prevalent should exercise caution.

“Anyone who is planning to travel to a country with active Zika virus transmission should consult with their health care provider before leaving, especially if they are pregnant or are considering becoming pregnant,” Relucio said.

Victoria Colliver is a San Francisco Chronicle staff writer. Email: vcolliver@sfchronicle.com Twitter: @vcolliver