The infection was detected through surveillance conducted by prefectural veterinary authority.
The virus was isolated from a pool of 10 nasal swabs directly collected randomly from pigs without clinical signs on 2 October 2009. The subtype H1 was confirmed by National Institute of Animal Health (NIAH) on 20 October 2009 while the subtype N1 was confirmed on 21 October 2009.
The affected farm, an integrated farrow-to-finish farm with approximately 100 breeding sows and a total of 1,000 pigs, is being under voluntary movement restraint. No abnormalities are observed in pigs within a 10km radius around the affected farm. Epidemiological investigations are continuing.