A 13-year-old girl in British Columbia who was hospitalized with bird flu for several weeks late last year harbored a mutated version of the virus, according to a report published this week in the New England Journal of Medicine. 

The case was Canada’s first recorded human infection of avian influenza, which has infected at least 66 people in the United States since last March, according to the Centers for Disease Control and Prevention. This includes the nation’s first severe case, in…