A fourth Sonoma County resident has died of H1N1 flu-related illness, Sonoma County public health officials said Thursday.

The patient, who died Tuesday evening, was in her early 60s and had underlying health conditions that put her at risk of severe illness, officials said.

The total number of severe flu cases in Sonoma County is now up to 15, officials said. A severe case is one where the patient dies or requires treatment in an intensive care unit.

The season's first flu-related death occurred Jan. 8, when Matthew "Matty" Walker, 23, of Santa Rosa died after he contracted the H1N1 flu virus. Health officials said Walker had no previous medical conditions.

Two subsequent flu-related deaths, which took place on Jan. 12 and Jan. 15, both involved older residents with underlying health issues.

Nine new flu-related deaths were confirmed across the Bay Area on Wednesday, bringing the number of fatal cases to 29 as the onset of peak flu season loomed over the region, the San Jose Mercury News reported.

Health officials urged local residents to get vaccinated because it is the best way to avoid the flu. Vaccinations are available at health care facilities and pharmacies.

Officials also recommended taking the following steps to guard against the spread of flu:

-#8212; Wash your hands often with soap and water, especially after you cough or sneeze. Hand sanitizers also are effective.

-#8212; Cover your nose and mouth with a tissue when you cough or sneeze, and dispose of the tissue.

-#8212; Avoid spreading germs by not touching your eyes, nose or mouth. Avoid close contact with anyone who is sick.

-#8212; Do not go to work or send children to school while ill. If sick, stay home at least 24 hours after being free of fever or signs of a fever without the use of fever-reducing medications.

For more information and flu-shot availability, go to <a href="http://www.sonoma-county.org/health/topics/influenza.asp" target="_blank">www.sonoma-county.org/health/topics/influenza.asp</a>.