Health experts believe the transmission rate is low for people working in factories after a dessert company in Newark confirmed staff had tested postive for Covid-19.
Bakkavor Desserts in Jessop Way employs more than 1,600 people and the company will now be working with Public Health England moving forward.
The international company produces ready meals, soups, sauces and prepared fruit and vegetables as well as desserts and pizzas.
It supplies products to stores such as Tesco, Sainsbury's, Marks & Spencer and Waitrose.
The company said a small number of employees have tested positive for Covid-19, but did not provide an exact number.
Jonathan Gribbin, Director of Public Health Nottinghamshire, said he had been working closely with companies whose employees had been struck down with the virus.
He said: "What we have found across Nottinghamshire on several occasions now is that sometimes cases of coronavirus come to light through a workplace.
"But when we investigate that further we find that the workplace itself has very rigorous and extensive controls in place to ensure there isn't transmission in the workplace.
"As we follow up with some of these cases we frequently discover that the transmission, that their exposure to coronavirus, has actually taken place outside the workplace.
"It could be where employees live or how they have to travel, ending up having to share cars for example or it maybe outside of work.
"Employees who mix socially without having in place social distancing precautions.
"We are finding that in most cases, transmission takes place outside the work place environment.
"In Nottinghamshire we are fortunate to have a number of large food producers and because of their large work force.
"When we investigate that and assess the workplace - what we find is that they have good controls in place and discussing this with the people infected they have often ended up disclosing they probably dropped their guard in terms of the precautions they were suppose to be taking."
