Three Japanese males who arrived at Narita airport from Canada via the United States on Friday were confirmed to be infected with the new H1N1 strain of influenza, marking the first cases of so-called swine flu in Japan, the health ministry said Saturday.

The three — a high school teacher in his 40s and two teenage students from Osaka — had been in Oakville, Ontario, on a school trip since April 24. They returned via Detroit on a Northwest Airlines flight that landed at about 4:30 p.m.

The three, who had fevers and coughs, tested positive for influenza A during the onboard quarantine inspection and were taken to Japanese Red Cross Narita Hospital in Chiba Prefecture and isolated.