A large proportion of human salmonellosis have been attributed to the consumption of eggs or products containing or made with raw eggs.
There is a high risk of Salmonella contamination of cracked eggs. Furthermore, egg shell has tiny pores, through which Salmonella can migrate into the eggs in a contaminated environment. The bacteria can also be passed from the infected female hen directly into the substance of the egg before the shell has formed around it.
Control Programme in European egg-laying hens
A study in 2004-2005, conducted on commercial large-scale egg-laying hen farms in the 25 EU countries and Norway (EFSA), found a range of Salmonella levels in layer flocks between 0% and 79% and 20% of all farms were positive for S. Enteritidis and/or S. Typhimurium.
The European Union has two regulations for reducing and controlling the prevalence of salmonella in poultry and eggs ((EC) No 2006R1168 and No 2006R1177/) (link to legislation pages). Targets for the reduction of Salmonella in commercial laying flocks have been set. Every country will have to reduce the number of laying hens infected with Salmonella by a specific minimum percentage each year, with bigger reduction targets for countries with higher levels of Salmonella. The ultimate target is to reduce Salmonella levels to 2% or lower. There are fixed requirements for sampling, testing, recording and reporting for the control programme. All countries with Salmonella prevalence in commercial layers of above 10% have to vaccinate their layers. Antimicrobials may not be used as part of national salmonella control programmes. It is foreseen that eggs from Salmonella-infected flocks will be banned from being sold as table eggs in the EU from 2010 onwards, and will have to be sterilised if they are to be used for processing into egg products.
Salmonella have been found almost everywhere in the hatchery, including in breeder nest boxes, egg-storage rooms, hatchery trucks and in the hatchery itself. Bacteria spread to fertilised hatching eggs on the shell and may penetrate the shell. The bacteria can spread rapidly throughout the hatching cabinet by the circulation fans and remain in hatchery for years. Bacteria on the exterior of eggs or in eggshell membranes can be transmitted to chicks during pipping. To reduce Salmonella the chicks can be sprayed with live vaccine in the hatchery. Competitive exclusion cultures can also be successful. Sanitation procedures include disinfectant fogging systems and time controlled electrostatic spraying systems.
Report of the Task Force on Zoonoses Data Collection on the analysis of the baseline survey on the prevalence of Salmonella in slaughter pigs, in the EU, 2006-2007
Opinion of the Scientific Panel on biological hazards (BIOHAZ) related to “Risk assessment and mitigation options of Salmonella in pig production”
The Community Summary Report on Trends and Sources of Zoonoses and Zoonotic Agents in the European Union in 2007
DEFRA (Department for Environment, Food and Rural Affairs, UK). Code of Practice for the prevention and control of Salmonella on pig farms