Another cause for concern: flu season is underway in the U.S., and as seasonal influenza virus goes around, “humans, ourselves, could be a mixing vessel,” Davis says. If a person were simultaneously infected with bird flu and seasonal flu, the two viruses could theoretically combine to create a more transmissible strain.

British Columbia health officials have yet to identify a likely source of the infection, though none of the teen's contacts have tested positive for the virus so far.

A teenager in Canada, hospitalized with the country's first case of the H5N1 bird flu, is in critical condition. Health officials report his condition deteriorated rapidly despite having no prior health issues.

A Canadian teenager is hospitalized in critical condition with bird flu, health officials reported Tuesday. The teen has been receiving care at BC Children’s Hospital in Vancouver since Friday, the same day an initial test came back positive for H5 influenza.

A Canadian teen is hospitalized in critical condition with what is believed to be bird flu, a British Columbia health official said Tuesday. It’s not clear how the teenager picked up the virus, which has been detected recently in wild birds and poultry in the province,

A Canadian teen is severely ill with what is believed to be bird flu. The teen is not known to have had any contact with infected animals.