Chickens can become infected with Salmonella the same way humans get it – through the oral route. In addition to the oral route, chickens can become infected with Salmonella through their navel. Eggs can also become infected with salmonella even before their shells form.
Food is the most common vehicle for the spread of Salmonella, and eggs are the most common food implicated. As one authority points out, “Studies showed that the internal contents of eggs can be contaminated with Salmonella, and this contamination has been identified as a major risk factor in the emergence of human illness.”
Bacteria can be on the outside of a shell egg. That's because the egg exits the hen's body through the same passageway as feces is excreted. That's why eggs are required to be washed at the processing plant. All USDA graded eggs and most large volume processors follow the washing step with a sanitizing rinse at the processing plant. It is also possible for eggs to become infected by Salmonella Enteritidis fecal contamination through the pores of the shells after they're laid. SE also can be inside an uncracked, whole egg. Contamination of eggs may be due to bacteria within the hen's reproductive tract before the shell forms around the yolk and white. Salmonella doesn't make the hen sick.
Chicken is also a major cause of Salmonella. Beginning in 1998, the publisher of Consumer Reports magazine has conducted surveys and tested chicken at retail for Salmonella and Campylobacter. Its 2009 study found 14% of broiler chickens at grocery stores to contain Salmonella. A USDA Baseline Data Collection Program report done in 1994 documented Salmonella contamination on 20.0% of broiler-chicken carcasses. However, in 2009 the same USDA data collection survey showed the prevalence of Salmonella in broiler chickens at 7.5%. Additionally, turkey carries a lower risk with a prevalence of 1.66%.
In general, safe cooking and preparation of food can kill existing Salmonella bacteria and prevent it from spreading. Additionally, safe choices at the grocery store can greatly reduce the risk of Salmonella.
- Cook poultry until it reaches an internal temperature of 165 ºF.
- Cook eggs until they reach 160ºF or until the yoke is solid. Pasteurized eggs are available in some grocery stores.
- Do not eat or drink foods containing raw eggs. Examples include homemade eggnog, hollandaise sauce, and undercooked French toast.
- If you are served undercooked meat, poultry, or eggs in a restaurant don’t hesitate to send your food back to the kitchen for further cooking.
- Avoid cross-contamination. That means that you should never allow foods that will not be cooked (like salads) to encounter raw foods of animal origin (e.g., on dirty countertops, kitchen sinks, or cutting boards).
- Wash hands, kitchen work surfaces, and utensils with soap and water immediately after they have been in contact with raw foods of animal origin.