The strain identified is H7N2 low pathogenic AI. The strain is different to the highly pathogenic H5N1 strain that hit a Bernard Matthews turkey farm in February.
The farm has been placed under a 1km restriction zone and the remaining birds on the farm have been slaughtered.
Health Protection Agency tests on the farm workers revealed four out of the nine tested were infected with AI.
Pat Troop, chief executive of the Health Protection Agency said: "These test results confirm that human infection with the AI virus has occurred. The virus does not transmit easily to humans. Worldwide, almost all human H7N2 infections documented so far, including those associated with this most recent incident, have been associated with infected poultry.
"Three of the nine individuals were initially hospitalised. They have all, however, now been discharged."
Poultry keepers are being reminded to report any suspicious signs of a notifiable avian disease to their local Animal Health Divisional Office. Members of the National Poultry Register will receive updates by text.