Six more flu-related deaths have been recorded in San Mateo, San Francisco, Sonoma and Contra Costa counties, health officials said Wednesday.
In Sonoma County a fourth flu death was reported Tuesday evening, health officials said Wednesday.
The most recent death was a woman in her early 60s who had an underlying medical issue. She was infected with the H1N1 strain.
Others who were fatally infected were a 61-year-old woman, a 54-year-old man and a 23-year-old man, health officials said.
Three additional deaths in Contra Costa County have been linked to the flu this month, county health services officials said.
Five people younger than 65 have died since December, health officials said.
The new Contra Costa cases were a man in his 30s, a man in his 50s and woman in her 60s. The first two deaths were a man and a woman both in their 40s.
San Mateo County Health System spokeswoman Robyn Thaw said there have been four flu-related deaths in the county as of Wednesday.
Three of those fatally infected had underlying medical conditions and three of them had contracted the H1N1 strain, known as "swine flu."
H1N1 first emerged in humans in 2009 and appears to be more dangerous to young and middle-age adults than other flu strains.
In San Francisco, the second flu-related death of the season was recorded Wednesday, city health officials said.
The victim, a man who was not elderly but who had an underlying medical condition, died of an unknown strain of the flu virus, according to public health department.
The department was notified of the death late Tuesday.
The city's first death since the start of flu season was reported in late December. The victim in that case was an adult who also had an underlying medical issue, health officials said.
That death was connected to the H1N1 strain.
Health officials are encouraging everyone to get vaccinated. The flu shot includes protection against H1N1 and takes two weeks from the date of inoculation to take full effect.
The flu season typically peaks January through March.
There have been 30 flu-related deaths this season throughout the Bay Area region.
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