In addition to the workers that have tested positive, five other employees are awaiting results. Further tests are taking place on site.
Banham Poultry is the latest food manufacturer to be hit by cases of the virus.
2 Sisters Food Group has confirmed 152 cases related to its site in Coupar Angus.
It decided to temporarily suspend operations to prevent the spread of the virus.
In June, 2 Sisters suspended production at its chicken plant in Llangeli, Wales following an outbreak there.
Greencore has suspended processing at its Northampton site following almost 300 confirmed cases there.
Louise Smith, director of public health for Norfolk, said: “We are working with colleagues at Public Health England, the NHS and Breckland Council following an outbreak of coronavirus at Banham Poultry in Attleborough.
“The management team at Banham Poultry has acted quickly to help prevent the spread of the virus and is working closely with us to trace the contacts of those who have tested positive.”
She said health officials were monitoring the situation and taking action to prevent further transmission both at the site and in the community.
Blaine van Rensburg, managing director of Banham Poultry said: “The safety of our staff, customers, and the wider public is really important to us and we are working with public health authorities to make sure we are doing absolutely everything we can and following all of the correct procedures. We have already invested in a range of procedures and protective equipment to keep our staff as safe as possible.
“The business remains open and operating and we are doing everything we can to prevent the further spread of the virus.”
Fresh food supplier Bakkavor and biscuit manufacturer Pladis have also confirmed new COVID-19 cases.