San Francisco confirms H5N1 bird flu case in child with unknown exposure

A human case of H5N1 bird flu has been reported in a San Francisco child, according to health officials. The source of the infection remains unknown.

The child experienced symptoms of fever and conjunctivitis but did not require hospitalization and has since fully recovered, the San Francisco Department of Public Health (SFDPH) said on Friday. The child tested positive for H5N1 after tests conducted at a SFDPH health laboratory, with confirmation pending from the Centers for Disease Control and Prevention (CDC).

An initial investigation has not determined how the child contracted the H5N1 bird flu, according to the SFDPH, which added that “the Department is continuing to investigate, including assessing all close contacts.”

A newer strain of H5N1 bird flu—clade 2.3.4.4b—has raised concern due to its global spread and an increasing number of cases in mammals, including hundreds of outbreaks among dairy cows in the U.S. since 2024. There has also been a limited but growing number of human cases linked to contact with birds or cows.

LINK: A list of all human cases of H5N1 bird flu since 2021

The new variant has resulted in 86 human cases worldwide since 2022, with the U.S. reporting the majority (74 cases), including the first death in Louisiana. Other countries with confirmed cases of the new variant include Canada, the U.K., Spain, China, Ecuador, and Chile.

This new case in San Francisco follows reports of an H5N1-related human death in Cambodia. The 28-year-old man died on Friday. He had contact with sick chickens, according to the country’s health ministry.

It is not yet known which strain was involved in Cambodia’s case, but it is likely clade 2.3.2.1c, an older variant endemic to the country. No H5N1 cases were reported in Cambodia between 2014 and 2022, but since then, 17 cases have been identified, including 11 in the past year.