Influenza is turning up in Santa Clara County sewage at higher levels than it did a week earlier, one of several signs that flu is reaching the Bay Area ahead of its usual winter peak.
Federal wastewater surveillance for the week ending Sept. 26 shows influenza A rising at all four county treatment plants in the CDC's network. Readings ranged from low to moderate. At the largest site, which serves roughly 1.5 million people, the measurement climbed to the low range from a lower reading the week before.
A smaller plant covering about 236,000 residents reached the moderate range. SFGATE also reported elevated flu levels in wastewater from Palo Alto and San Jose.
Regionally, state lab data through mid-September put the Bay Area's share of positive flu tests at 5.4%, the highest of any California region and above the 3.9% statewide figure. Hospital admissions for flu were still rated very low.
San Francisco health officials on Thursday reported the city's first flu-related death of the 2026-27 season, an adult whose identity was not released.
The CDC advises everyone 6 months and older to get a flu shot by the end of October. State figures show fewer than one in 10 Bay Area residents had done so as of Sept. 19.