Most types of Salmonella live in the intestinal tracts of animals and birds. Prior to the 1970s, fecal contamination of eggshells was the primary source of Salmonella infection associated with eggs. In the 1970s, however, procedures for cleaning and inspecting eggs were implemented and the number of Salmonella infections associated with fecal contamination of eggshells is now extremely rare.
In the late 1970s and early 1980s, researchers discovered that Salmonella enteritidis has the capability to infect the ovaries of otherwise healthy hens and contaminate eggs before shells have formed. Studies have shown that Salmonellaenteritidis can be found inside intact and disinfected grade A eggs. St. Louis, et al. reported in 1988:
From 1976 to 1986, reported Salmonella enteritidis infections increased more than sixfold in the northeastern United States. From January 1985 to May 1987, sixty-five foodborne outbreaks of S enteritidis were reported in the Northeast that were associated with 2119 cases and 11 deaths. Twenty-seven (77%) of the 35 outbreaks with identified food vehicles were caused by Grade A shell eggs or foods that contained such eggs.*
According to the Centers for Disease Control and Prevention (CDC), only a small number of hens are infected at any one time, and an infected hen lays contaminated eggs only sporadically. Estimates are that one in 10,000 eggs produced in the northeastern United States may be internally contaminated with Salmonella enteritidis. Eggs from other parts of the US have lower contamination rates.
A nationwide Salmonella Enteritidis outbreak was traced to eggs produced by Wright County Egg and Hillandale Farms in 2010. At least 1,609 Salmonella cases were documented across the country, and the two companies recalled a total of 550 million eggs for potential Salmonella contamination. The eggs had been distributed to retail outlets and restaurants, and several Salmonella outbreaks originally associated with restaurants were later determined to be caused by the contaminated eggs. See Wright County Egg Salmonella Lawsuits and Litigation
In 2003, a Salmonella enteritidis outbreak in southeastern Washington State was traced to the consumption of fried ice cream served at a banquet held at Bogey’s Restaurantin Clarkston, Washington. The Washington Department of Health (WDOH) investigated the outbreak, and concluded that over 58 people had become ill with Salmonellainfections after attending the banquet. The environmental investigation revealed that in the preparation of the dessert, scooped ice cream was dunked in an egg mixture that had been pooled the day before and stored in a five gallon bucket. Prior pooling of eggs is a violation of the Washington State Food Code. WDOH ultimately stated that undercooked, “pooled” eggs used in the making of fried ice cream were the cause of the Salmonella outbreak, but did not rule out the possibility that an infected food handler could have been the source. See Quality Inn Salmonella Outbreak Lawsuits.
Unpasteurized eggs should only be considered safe if they have been cooked to a temperature of 160 degrees Fahrenheit. Eating eggs prepared with a runny yolk is a risk factor for Salmonella infection. Undercooked egg whites and yolks have both been associated with Salmonella enteritidis infections.
The CDC recommends following the below food safety procedures to prevent Salmonella infection from contaminated eggs:
- Keep eggs refrigerated.
- Discard cracked or dirty eggs.
- Wash hands and cooking utensils with soap and water after contact with raw eggs.
- Eat eggs promptly after cooking.
- Refrigerated unused or leftover egg-containing foods within 2 hours of cooking them. .
- Avoid eating raw eggs in foods such as homemade ice cream or eggnog. .
- Avoid restaurant dishes made with raw or undercooked, unpasteurized eggs, such as Caesar salad or hollandaise sauce.
* St. Louis ME, Morse DL, Potter ME, et al. The emergence of grade A eggs as a major source of Salmonella Enteritidis infections: new implications for the control of salmonellosis. JAMA 1988;259:2103--7.