The health ministry said on Sunday that another Osaka student has been infected with A/H1N1 flu, bringing to four the confirmed cases of the new strain of influenza in Japan.

On Saturday afternoon, the male student ran a fever of about 38 degrees Celsius, and further tests conducted by the National Institute of Infectious Diseases confirmed that he has contracted the new flu.

The student traveled on the Northwest Airlines flight with the three patients of a teacher and two other male students, who became confirmed cases of the new flu Saturday, and arrived Friday at Narita international airport.

The four, along with 32 others, had stayed in Oakville, Canada, on a school trip from April 24 before returning to Japan from Detroit, the United States.

Another 48 people on the same flight are being kept in quarantine at an accommodation facility near the airport and expected to be monitored for 10 days while all the other 358 passengers and crew are undergoing further tests to determine their conditions.

On Saturday, the health ministry reported Japan's first three cases of the new flu to the World Health Organization (WHO), which later added Japan to its list of countries that have reported laboratory confirmations of new flu cases.