H3N2 influenza virus particles.

Flu season has arrived with a vengeance in the Bay Area, with multiple signs pointing to a potential surge in infections.

This week the San Francisco Health Department reported the season’s first flu-related fatality, as flu-related hospitalizations rose dramatically to 2.39 per 100,000 residents as of Saturday from a rate of 0.12 per 100,000 in the middle of September. 

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“This sad news reminds us that respiratory viruses such as flu and COVID should be taken very seriously, especially for people who are at higher risk of getting sick,” San Francisco Health Officer Dr. Susan Philip said in an emailed statement Thursday. 

Dr. Monica Gandhi, an infectious disease expert at UC San Francisco, told SFGATE by phone Friday that flu activity normally ramps up closer to the winter holiday season, in November or December.

“I’m very surprised by this flu death because that’s very early,” she told SFGATE. “People are just getting their vaccines right now.” 

Influenza levels started to rise in the local wastewater last........

© SFGate