San Francisco public‑health officials say H5N1 risk to general public remains low after one local case

San Francisco’s health officer on March 3 told the Health Commission the city has recorded one human H5N1 avian influenza case but that the risk to the general public remains low.

Dr. Susan Philip said the case was detected through enhanced surveillance in the city’s public‑health laboratory and later confirmed by the Centers for Disease Control and Prevention as genotype B3, a strain linked to recent outbreaks in California dairy cattle. The case was a child in San Francisco with fever and conjunctivitis; symptoms resolved within a week and no secondary infections were found after extensive contact tracing and serology testing.

At a national level, Philip said there were 70 confirmed human cases of H5N1 in the United States as of Feb. 26, with 38 in California. She said more than 12,000 wild birds had tested positive and that about 973 dairy herds in the U.S. had been affected as of late February. Most U.S. human cases have been associated with animal exposures — particularly dairy workers — and almost all reported illnesses have been mild; there have been four hospitalizations and one death reported in Louisiana.

Philip described three planning scenarios the department is preparing for: (1) isolated human cases like San Francisco’s; (2) a virus that gains some ability to transmit person‑to‑person, requiring heightened response; and (3) a virus that transmits widely and causes high morbidity or mortality, which would trigger full response operations. The department has run a tabletop exercise and convened an incident management team with subject‑matter experts across DPH.

San Francisco is using enhanced laboratory surveillance — subtyping influenza A specimens and testing a sample of positive influenza A specimens from hospitals and clinics — to look for H5 subtypes. The health officer also noted wastewater monitoring as a complementary signal, and said the H5 (possible H5N1) signal in the city’s wastewater remains very low.

Philip said vaccine development and stockpile discussions are ongoing at the federal level; she reported there is a national stockpile of doses reserved but that those have not been federally released for wide use as of the briefing. She also said antiviral treatment (oseltamivir) has so far been effective in reported cases and that DPH is planning distribution scenarios should treatment supplies become constrained.

The department emphasized that San Francisco’s one detected case produced no evidence of person‑to‑person transmission after extensive follow‑up. Nonetheless, Philip said influenza viruses mutate and that DPH will continue monitoring, preparing for multiple scenarios and updating the commission as needed.

Source: Presentation by Dr. Susan Philip, San Francisco Health Officer, March 3, 2025, San Francisco Health Commission meeting.