The health ministry announced Sunday that a 4-month-old American baby quarantined at a U.S. air base in Tokyo has seasonal influenza, ruling out the possibility of infection with swine flu.
With the case cleared, no confirmed cases of the new H1N1 flu have been reported in Japan.
The baby arrived at Yokota Air Base from the United States on Friday and was feared to represent the first case of swine flu in Japan.
Test samples from the infant were sent to the National Institute of Infectious Diseases in Tokyo on Saturday for more elaborate examinations.
The baby and mother were isolated at a medical facility at the base for treatment, according to the Foreign Ministry.
The infant was reportedly showing signs of recovering.
Besides the pair, 13 other passengers sitting near the baby were also quarantined. No restrictions were imposed on other people on the chartered flight that carried 260 to 270 passengers.
Officials from U.S. Forces Japan said the samples would also be tested in the United States, a process expected to take five to eight days.