Fifteen counties have reported cases of dead birds or mosquitoes with West Nile Virus this year. That's almost double the number of counties with the virus at this time last year.
Dr. Vicki Kramer is with the California Department of Public Health.
"People should be concerned about the elevated West Nile Virus activity," urged Kramer, "and should take precautions especially when they're going to be outside at dawn and dusk when mosquitoes are most active."
Health officials said most people bitten by infected mosquitoes don't become ill, but some may develop flu-like symptoms and a small minority can become severely ill.