Each of the five deaths has involved a person under the age of 65. According to the San Mateo County Health System, four individuals had underlying medical conditions and one person had no known underlying medical conditions.
Four of the influenza cases have been confirmed as H1N1, or swine flu, while strain information was not available for one case, according to the health system. San Mateo County has had 18 flu-related hospitalizations in the intensive care unit this season. San Francisco has reported three influenza-related deaths of non-elderly adults this season.
The first death in December was confirmed to be due to swine flu, the San Francisco Department of Public Health said. Bay Area county health departments reported at least 34 flu deaths have occurred this winter in the region.