Most human cases of bird flu in North America have been mild, a fact that’s underscored by a new study of the first 46 confirmed human H5N1 infections in the United States this year. But the case of an ill Canadian teen stands out because of its severity and because the source of exposure remains a mystery.

As for testing, the girl's first swab at BC Children's was positive for influenza A but negative for H1 or H3 disease. Further polymerase chain reaction testing for flu, COVID, and respiratory syncytial virus showed a cycle threshold (Ct) value of 27.1, suggesting a relatively high viral load, which prompted further subtyping, revealing H5 disease.

In 2024, at least 66 human cases of bird flu have been reported in the United States, each one raising the risk of another pandemic like COVID-19. So far, most cases have been described as “mild,” which means they weren't hospitalized.

Genetic analysis of H5N1 bird flu viruses from a severely ill patient in Louisiana revealed multiple mutations that may enhance the virus’s ability to bind to human upper airway cells, the Centers for Disease Control and Prevention (CDC) reported on Thursday.

Los Angeles County health officials have identified three more cats with presumptive H5N1; the source of the virus has not yet determined, but experts suspect raw meat.

As of December 30, the CDC has confirmed 66 human cases of the bird flu virus in the United States. Most of them were mild infections among dairy workers and others who had contact with infected animals.

Health experts are raising concerns after genetic sampling of the first severe H5N1 bird flu case in the U.S. Map shows US states where 'damaging' Arctic blast will hit first - and more to come Look inside the Breakers,