Greencore said 79 employees tested positive for the NHS before the company established a personal testing program.
The test returned 213 additional effects, bringing the total number of effects to 292.
Greencore told Sky News that the company is still waiting for some effects to return. A spokesman who could not verify the number still said it was less than 100.
The company said in a statement: “Due to the growing number of COVID-19 instances in the Northampton area, we have taken the resolution to proactively initiate all colleagues on our Northampton site.
“We can verify that several colleagues have tested for the virus and are now self- isolating the virus.
“We work heavily with PHE East Midlands, the Northamptonshire County Council and the Northampton Township Council, which are completely the checks we have on the site.”
The company added, “Just in case, we seek contacts without delay and ask our potentially involved colleagues to isolate themselves.”
“All Greencore sites have extensive social distance measures, strict hygiene procedures and normal temperature control, and we are doing everything we can to protect our employees.
“As always, the physical form and well-being of our colleagues is our most sensible priority.”
Lucy Wightman, director of public fitness at Northamptonshire County Council, said workers were asked to “act now” after the number of cases shown in the city increased from 66 in the week ending 2 August to 85 in the week ending 9 August.
She said: “We are working with Greencore colleagues in Northampton after the discovery of a COVID-19 outbreak in the workplace.
“Public Health England Midlands has supported its Greencore colleagues in managing the epidemic.
“This was complemented by the local infection prevention and control team and environmental fitness colleagues at Northampton Borough Council.”
She added: “It is transparent that Greencore has put in place very effective measures and continues to paint incredibly hard to overcome the needs needed to be coVID-19 safe in the painting position.
“The municipality of Northampton has noticed a large number of cases in the last 4 weeks and citizens and workers have been asked to ‘act now’ to stick to additional measures, in order to provide a local closure or additional government intervention.
Greencore describes itself as the world’s largest sandwich manufacturer, generating nearly 4 million sandwiches each week in its supermarket factories, convenience stores, garages, coffee chains, catering services and airlines.
The company’s outbreak occurs when a banana distribution center in Coventry operates publicly to involve and manage a COVID-19 outbreak.
All Fyffes Group Limited staff at Richardson Way, Cross Point Business Park, will need to be tested as a precautionary measure after 10 staff members tested positive for the virus.
The company’s control works largely with the public fitness of Coventry City Council, Public Health England (PHE) Midlands and Health and Safety Executive (HSE).
Coronavirus outbreaks have occurred in food processing plants in Wisbech, Wrexham, Cleckheaton, Merthyr Tydfil and Llangefni
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Developments in Northampton and Coventry occur when the World Health Organization (WHO) minimized the possibility of coronavirus crashing in food packaging.
WHO Emergency Programme Director Mike Ryan said at a briefing in Geneva: “People are not afraid of food, packaging or food processing or delivery.
“There is no evidence that food or the food chain is involved in the transmission of this virus. And other people feel comfortable and safe.”