03.09.2011

In a study published in the journal Applied and Environmental Microbiology, June 2011, p. 3896–3897 German researchers analyzed the prevalence of thermotolerant Campylobacter spp. compared that of to Salmonella spp. in raw yolk and on eggshells. The aim of this study was to collect data about the prevalence of thermotolerant Campylobacter spp. in raw yolk and in parallel on the eggshells. These data can be used for a risk assessment concerning possible human foodborne campylobacteriosis via cross-contamination of ready-to eat food or via eating undercooked eggs or food produced with raw egg.
Thermotolerant Campylobacter spp. are one of the most important causes of food-borne disease in Germany. In 2008, the European Food Safety Authority (EFSA) registered 190,566 cases of human campylobacteriosis from 24 countries and 131,468 cases of human salmonellosis from 28 European countries. During the last 5 years, the number of Salmonella infections in Europe continuously and significantly decreased, while the number of Campylobacter cases remained on a high level. One important reservoir of thermotolerant Campylobacter spp. is poultry, mainly broilers and laying hens.
In comparison to the knowledge about the contamination rate of chicken meat, there are only a few data available about the prevalence of thermotolerant Campylobacter spp. on the eggshell or in the egg content itself.
During the years 2009 and 2010, 2,710 eggs were investigated for the presence of thermotolerant Campylobacter spp. and the same number of eggs was investigated for the presence of Salmonella spp. by using cultural and molecular methods.
Thermotolerant Campylobacter spp. were isolated from 11 (4.1%) eggshell samples but not from any of the egg yolk samples. Eight isolates were confirmed as Campylobacter coli and three isolates as Campylobacter jejuni. Four positive samples were sold as free-range eggs and seven positive samples as
barn eggs. Salmonella Enteritidis was found in three eggshell samples (1.1%) but not in any of the egg yolk samples. Two positive samples originated from hens kept in battery cages and one sample from hens kept in deep litter.
The results of this study show that Campylobacter spp. can be found regularly on the eggshells of table eggs. The isolation rate in this study was much higher than the prevalence of thermotolerant Campylobacter spp. in bovine meat (0.3%), pig meat (0.5%), milk (2.3%), and milk products (1.2%) reported by EFSA for the year 2008. The contamination rate was also found to be much higher (4.1%) than the contamination rate of eggshells for Salmonella spp. investigated in the same period (1.1%). Thermotolerant Campylobacter spp. was found only on the eggshell and not in the egg content. But like the situation with broiler meat, it can be expected that the risk for food-borne human campylobacteriosis is much higher via cross-contamination of ready to eat products than via the consumption of raw or undercooked poultry meat. Like the situation with Salmonella spp., it can be presumed that contamination of the egg content is based mostly on transmission of bacteria from the eggshell to the egg content during the cracking of the eggshell. Therefore, contamination of the eggshell should be much more important for a human food-borne infection than the presumed very low contamination rate and short viability of thermotolerant Campylobacter spp.