People are coming back to the San Francisco Bay Area from holiday travel around the country. They’re bringing back good cheer, East Coast souvenirs…and influenza!
Multiple surveillance systems are pointing the same direction: influenza activity is rising very fast, and the Bay Area is showing early signals — especially in wastewater and also flu tests.
The California Department of Public Health (CDPH) says seasonal influenza activity is increasing in all California regions, and flags a notable rise in test positivity among children. CDPH also notes hospitalizations are currently low, but expected to increase. (This is a statewide view, but it includes the Bay Area.)
CDPH also posted a heads-up that their dashboard update cadence is shifting around the holiday — with late-December and early-January updates landing on December 29, 2025 and January 5, 2026. So we may not know the full extent of the recent spike until after the New Year.
The Bay Area also appears to have the highest rates of flu in the state at the moment, entering the High category.
One of the earliest signals tends to be wastewater, because it can rise before people start testing (or going to the doctor).
KTVU reports that influenza A is showing up at high levels in Bay Area wastewater, with hot spots including San Jose, Palo Alto, Fremont, San Francisco, and parts of the North Bay (from San Rafael to Vallejo).
That usually presages later spikes in positive tests, unfortunately, hospitalizations.
Both CDPH and the CDC have been pointing at the same likely driver: an H3N2 influenza A strain known as subclade K, which has been linked to an early, active season in parts of the Northern Hemisphere.
What to do? There’s still time to get the flu shot if you want one. And the arrival of flu means it’s time to pretend it’s 2021 and enact your full suite of measures: washing your hands (which, honestly, you should do anyway), staying home if you’re sick, and generally playing it safe when it comes to illness.
