Japan's Health Ministry said Thursday that 93 poultry farm workers may have been infected with a mild form of bird flu last year.
The ministry had said in a preliminary report in January that 77 people were exposed to and possibly infected with the H5N2 virus, which was not previously known to infect humans. It is milder than the virulent H5N1 strain that has recently spread from Asia to Europe.
Most of the 77 were poultry farm workers in Ibaraki and Saitama prefectures near Tokyo.
After conducting tests on more workers, the ministry found that 16 more in Ibaraki may have caught H5N2, according to ministry official Hiroshi Takimoto.
Tests on the workers were positive for H5N2 antibodies, indicating they were previously exposed, Takimoto said.
While exposure carries with it the possibility of infection and illness, he said none had tested positive for the virus itself or had developed flu symptoms.
The ministry had been testing chicken farm workers since a bird flu outbreak in Ibaraki in June last year.
The disease hit Japan in 2004 for the first time in decades. There has been one confirmed human case involving the H5N1 virus in December 2004, but no reported human deaths.
About 5.7 million birds have been destroyed in Ibaraki following the H5N2 outbreaks.