The H5N1 virus that infected a Canadian teen appears not to have spread, but it shows signs of mutation that makes flu virologists nervous.

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A teenager in British Columbia was hospitalized in critical condition with the disease, and officials were working to find out how the person was exposed to the virus.

A Canadian teenager infected with bird flu — that country’s first case involving a locally acquired infection — is in critical condition and experiencing difficulty breathing, health officials said Tuesday.

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.

British Columbia health officer Dr. Bonnie Henry shared in a news conference that a teenager, who contracted the first presumptive case of bird flu in Canada, was in critical condition after developing 'acute respiratory distress.