Health officials now report flu deaths in all nine Bay Area counties.
Napa County has recorded its first death, an 84-year-old man with medical issues.
The county has not yet confirmed what strain the man had but is working on the assumption that it is probably H1N1, a spokeswoman for the county said.
In Contra Costa County, a second person died, a 48-year-old man. That death was confirmed on Tuesday as being linked to the H1N1 strain.
MORE: Flu Prevention Tips
And, in Sonoma County, a third person succumbed to the virus, a 51-year-old man also with medical issues.
This raises the total number of flu deaths in the Bay Area to 20.
- Santa Clara County - 4 deaths
- Alameda County - 3 deaths
- Marin County - 2 deaths
- San Mateo County - 3 deaths
- San Francisco - 1 death
- Contra Costa County - 2 deaths
- Solano County - 1 death
- Sonoma County - 3 deaths
- Napa County - 1 death
The majority of this season's deaths have been linked to swine flu, which first emerged in 2009. The H1N1 strain is known to be more dangerous to young and middle-age adults than other strains of the flu.
Health officials are urging everyone ages 6 months and older to get vaccinated. Those considered at highest risk are those 65 and older, children less than two years old, pregnant women and those with medical conditions like asthma, heart disease and weakened immune systems.
The peak of flu season is between January and March, and the vaccine takes about two weeks after inoculation to be fully effective, according to health officials.
For more information on flu prevention, click here.
Bay City News contributed to this report.