Large farms and high stocking densities bring increased risk of salmonella spread in layer flocks, according to a scientific report for the EU.
The report has been produced by the Scientific Panel on Biological Hazards (BIOHAZ) at the request of the European Commission.
This was in response to an increase in confirmed human Salmonellosis cases in the EU since 2014.
Salmonella contamination has been a recurring problem in egg imports from Europe to the United Kingdom.
More than 160 cases of salmonella in the United Kingdom since 2014 were linked to an egg packing centre in Poland. Other outbreaks have been traced to eggs imported from Spain.
In August last year, lawyers confirmed that victims of a salmonella outbreak linked to imported eggs had won thousands of pounds in damages.