A total of 77 people may have been infected by bird flu virus, but they have shown no symptoms and will not spread the disease to other people, a government report said Tuesday.

The report compiled by the Health Ministry and the National Institute of Infectious Diseases was based on inspection of their blood samples that they may have been infected by the H5N2 strain of the avian influenza virus, which is a weaker type compared with the H5N1 virus.

Their antibody were positive, but none virus has been detected, the report said.

The investigation involved about 350 people who are linked to poultry industry and sanitary workers in the Ibaraki and Saitama prefectures where poultry farms have been hit by bird flu.