San Diego County health officials said 10 birds have tested positive for the disease there in the past week and their locations are raising fears that infected birds are becoming more frequent in cities, The San Diego Union-Tribune said Tuesday.

The birds were found in the California cities of Bonsall, Fallbrook, Vista, Oceanside, Carlsbad, Cardiff, Kearny Mesa and Bonita, officials said, and included nine crows and a barn owl.

"We are finding more evidence of the virus in urban areas rather than rural and mountain areas," Gary Erbeck, director of the county's Department of Environmental Health, told the newspaper.

Officials say nearly 3,700 people in the United States became seriously ill from the bites of West Nile-infected mosquitoes in 2007, with 124 deaths, including 20 in California, attributed the disease.