TOKYO - Japan confirmed its fourth case of H1N1 flu Sunday in a teenager who recently returned from a school trip to Canada.
Three others in the group that visited Canada were earlier identified as having the virus.
The patient, who was not identified, is being quarantined at a hospital near the airport, the Japanese Health and Welfare Ministry said. He had been in Oakville, Ontario, since April 24 and returned on Friday on a Northwest Airlines flight from Detroit.
A lab at the National Institute of Infectious Diseases confirmed he had the same strain of the disease identified in the deaths of 53 people worldwide, most of them in Mexico, the epicentre of the disease.
The three teenage students and a teacher in his 40s had visited Ontario on a home stay program since last month with about 30 other students, and returned to Tokyo via Detroit on a Northwest Airlines flight, Health and Welfare Minister Yoichi Masuzoe told a televised news conference.
They had participated in various programs hosted by a local high school in Oakville.
Andrew Morrison, a spokesman for the Ontario Ministry of Health, said Friday that Ontario and federal health officials were investigating whether the individuals were infected while in Canada.
Japan has taken 49 other passengers who were on the plane to hospitals for further tests, and has tracked down all but four of the passengers on the flight who remained in Japan.
The governments in China and Hong Kong said they had quarantined travellers who were on the flight and continued on to their countries.
Hong Kong is keeping two people under observation who have not shown any flu symptoms.
China's Health Ministry said it had placed seven people under observation. Their conditions were not immediately known.
