Japanese authorities scrambled Saturday to track travelers who arrived on the same flight as three people diagnosed with the country's first confirmed cases of swine flu. Australia also joined the ranks of affected countries with its first confirmed case. Authorities in Tokyo quarantined a high school teacher and two teenage students who returned Friday from a school trip to Canada after they tested positive at the airport. In the Canadian province of Alberta, the chief medical officer on Friday confirmed the death of a woman infected with the virus. The woman, who was in her 30s and had other health problems, died April 28. Officials said she had not left the country recently, but could not confirm whether she was in contact with anyone who had recently returned from Mexico, where swine flu has hit hardest. Dr. Andre Corriveau, Alberta's chief health officer, said 300 people who attended the woman's wake were being monitored for signs of the illness. The World Health Organization has said based on past outbreaks, it is possible that a third of the world's population, or about 2 billion people, could become infected if this outbreak turns into a two-year pandemic. Independent experts agreed it was possible but pointed out that many would not show any symptoms.