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.

Initial testing had indicated the teenager’s infection was from bird flu and was confirmed in further testing, the Public Health Agency of Canada said in a statement. The teen has been hospitalized in Vancouver since Friday and was reported in critical condition on Tuesday.

A Canadian teenager is hospitalized in critical condition with suspected bird flu, health officials reported Tuesday.

A Canadian teen is hospitalized in critical condition with what is believed to be bird flu. British Columbia health officials said Tuesday it’s not clear how the teen picked up the virus .

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.