Highly Pathogenic Avian Influenza A(H5N1) Virus Infection in a Child with No Known Exposure

What is already known about this topic?

As of January 1, 2025, 37 human cases of highly pathogenic avian influenza (HPAI) A(H5N1) had been detected in California, none of which occurred in San Francisco.

What is added by this report?

On January 9, 2025, a case of HPAI A(H5N1) infection was identified in a school-aged child in San Francisco through enhanced surveillance (influenza A virus subtyping of a sample of specimens weekly). No source of exposure was identified, and investigations found no laboratory evidence of human-to-human transmission among close contacts.

What are the implications for public health practice?

Enhanced surveillance and timely subtyping of a subset of influenza A–positive specimens, including specimens from persons without known A(H5N1) exposure, are important to detect avian influenza A virus infections. Public health investigations are critical to monitoring for human-to-human transmission.