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Salmonella serotype Enteritidis

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Salmonella serotype Enteritidis infection

Salmonella serotype Enteritidis (SE) is one of the most common serotypes of Salmonella bacteria reported worldwide. During in the 1980s, SE emerged as an important cause of human illness in the United States.  The number of outbreaks of SE rose dramatically during that time, beginning in the northeastern states and then spreading west during the 1990s. SE illness now occurs in most regions of the country. Consumers should be aware of the disease and learn how to minimize the chances of becoming ill.

Eggs have been the most common food source linked to SE infections. SE can be inside perfectly normal-appearing eggs. If eggs contaminated with SE are eaten raw or lightly cooked (runny egg whites or yolks), the bacterium can cause illness. Since the early 2000s, poultry has also been found to be a common food source for SE infections. Multiple other, less frequently identified sources include raw milk, pork, beef, sprouts, and raw almonds. International travel and contact with reptiles have also been associated with SE infection.

A person infected with the Salmonella bacterium usually has fever, abdominal cramps, and diarrhea beginning 12 to 72 hours after consuming a contaminated food or beverage. The illness usually lasts 4 to 7 days, and most persons recover without antibiotic treatment. However, the diarrhea can be severe, and the person may be ill enough to require hospitalization.

The elderly, infants, and those with impaired immune systems may have a more severe illness. In these patients, the infection may spread from the intestines to the blood stream, and then to other body sites and can cause death unless the person is treated promptly with antibiotics.

Egg and chicken contamination

Most types of Salmonella live in the intestinal tracts of animals and birds and are transmitted to humans when feces from animals directly or indirectly contaminate foods that humans eat. For example, if chicken feces get on the outside of the shell of eggs, Salmonella in the feces can contaminate the egg through cracks in the shell.  This used to be a common problem.  However, stringent procedures for cleaning and inspecting eggs were implemented in the 1970s and have made illness from Salmonella caused by chicken feces on the outside of egg shells extremely rare. However, unlike Salmonella infections from eggs in past decades, the epidemic that started in the 1980s and continues to cause illnesses today is due to SE being inside of intact grade A eggs with clean shells. The reason is that SE can silently infect the ovaries of healthy appearing hens and contaminate the inside of eggs before the shells are formed.

SE infection is present in hens in most areas in the United States. An estimated one in 20,000 eggs is internally contaminated. Only a small number of hens might be infected at any given time, and an infected hen can lay many normal eggs while only occasionally laying eggs contaminated with SE.

Chickens raised for meat, called broiler chickens, can also be contaminated with SE. During the period 2000–2005, as eating chicken emerged as a risk factor for SE infection, studies by the US Department of Agriculture’s Food Safety and Inspection Service (USDA-FSIS) found an average of one in eight sampled broiler chickens were contaminated with Salmonella, and of the Salmonella-positive chickens, one in 20 were contaminated with SE.

Who can be infected?

Anyone can get a Salmonella infection, but the elderly, infants, and persons with impaired immune systems are at increased risk for serious illness. In these persons, a relatively small number of Salmonella bacteria can cause severe illness. In outbreaks, most of the deaths caused by SE have occurred among persons in nursing homes and hospitals. Egg-containing dishes prepared for any of these high-risk persons, whether in hospitals, nursing homes, restaurants, or at home, should use pasteurized eggs. Poultry dishes prepared for these high-risk persons should be cooked thoroughly, to a minimum internal temperature of 165º F (74ºC).

What is the risk?

Eggs

According to estimates from the 1990s, about one in 20,000 eggs is contaminated with SE. With approximately 65 billion eggs produced per year in the United States and 30% sent for pasteurization, an estimated 2.2 million individual eggs remain contaminated with SE. Many dishes made in restaurants or commercial or institutional kitchens, however, are made from pooled eggs, not from eggs prepared individually. One contaminated egg can contaminate an entire batch of pooled eggs. Everyone who eats eggs from that batch is at risk for illness. In individual eggs and pooled eggs that are thoroughly cooked (firm egg whites and yolks), SE will be destroyed and will not make a person sick. A person who eats eggs can lower the risk of SE infection by eating eggs that are thoroughly cooked, or by eating foods that are made from pasteurized eggs.

Chicken

Based on sampling at processing plants in 2007–2008, USDA-FSIS estimates that SE contaminates about one in 250 broiler chickens (USDA-FSIS communication, October 2010). Eating chicken prepared outside of the home, such as in restaurants, is a risk factor for becoming ill with SE. Lack of hand washing, not separating raw eggs or chicken from produce or other foods during preparation, and other unsafe food handling practices in homes and in commercial food establishments can increase risk of an SE infection.

What you can do to reduce risk

Eggs, poultry, meat, milk, and other foods are safe when handled properly. Shell eggs are safest when stored in the refrigerator, individually and thoroughly cooked, and promptly consumed after cooking. The larger the number of Salmonella bacteria present in the egg, the more likely the egg is to cause illness. Keeping eggs adequately refrigerated prevents any Salmonella present in the eggs from growing to higher numbers, so eggs should be refrigerated until they are needed. Cooking reduces the number of bacteria present in an egg; however, a lightly cooked egg with a runny egg white or yolk still poses a greater risk than a thoroughly cooked egg. Lightly cooked egg whites and yolks have both caused outbreaks of SE infections. Cooked eggs should be consumed promptly and not be held in the temperature range of 40 to 140ºF for more than 2 hours.

Cross-contamination occurs in the kitchen when unwashed hands or food preparation surfaces transfer SE from chicken to other foods. Keeping uncooked meat separate from other foods during storage and preparation can help prevent cross-contamination. Cooking chicken to 165ºF (74ºC) inside (use a thermometer!) kills SE and helps prevent illness. Prompt refrigeration of unused or leftover food prevents growth of bacteria. Dividing large amounts of leftovers into several shallow containers allows for quicker cooling in the refrigerator.

What else is being done?

Government agencies and the egg industry have taken steps to reduce SE outbreaks. These steps include the difficult task of identifying and removing infected hens from flocks that supply eggs and increasing quality assurance and sanitation measures. The US Food and Drug Administration (FDA) issued a rule that went into effect on July 9, 2010 that requires shell egg producers to implement measures on the farm to prevent SE from contaminating eggs. Eggs from commercial flocks that are known to be infected are pasteurized instead of being sold as grade A shell eggs. The rule also includes refrigeration requirements during storage and transportation.

The US Centers for Disease Control and Prevention (CDC) has advised state health departments, hospitals, and nursing homes about specific measures to reduce SE infection in humans. The CDC, FDA, and select laboratories across the country also collaborate to monitor contamination of meats sold in stores and other suppliers by SE and other contaminants.

State agencies and authorized laboratories of the USDA Animal and Plant Health Inspection Service’s National Poultry Improvement Plan, an industry-State-Federal cooperative program, certify participating breeding flocks and hatcheries of chickens that lay eggs as SE clean (“tested free”). USDA-FSIS regulates the safety of egg products, which are eggs removed from their shells for processing. USDA-FSIS also monitors contamination of broiler chickens with SE and other contaminants at all stages of chicken production at processing plants.

Research by these agencies and the egg industry is addressing many unanswered questions about SE, the infections in hens, and contaminated eggs. Informed consumers, food-service establishments, and public and private organizations are working together to reduce, and eventually eliminate, disease caused by this infectious organism.

Keys to avoiding Salmonella serotype Enteritidis infection

  • Buy eggs only from stores or other suppliers that keep them refrigerated.
  • Consumers can consider buying and using pasteurized shell eggs, which are available for purchase from certain stores and suppliers.
  • Keep eggs and chicken refrigerated.
  • Discard cracked or dirty eggs.
  • Wash hands and cutting boards, dishes, utensils, and counter tops with soap and water after contact with raw eggs or raw chicken.
  • Eggs should be thoroughly cooked until both the yolk and white are firm. Recipes containing eggs mixed with other foods should be cooked to an internal temperature of 160ºF (71ºC).
  • Chicken should be cooked until the internal temperature reaches 165ºF (74ºC).
  • Eat eggs promptly after cooking. Do not keep eggs warm or at room temperature for more than 2 hours.
  • Refrigerate unused or leftover foods promptly.
  • Avoid eating raw eggs (as in homemade ice cream or eggnog). Commercially manufactured ice cream and eggnog are made with pasteurized eggs.
  • Avoid restaurant dishes made with raw or lightly cooked, unpasteurized eggs. Restaurants should use pasteurized eggs in any recipe (such as Hollandaise sauce or Caesar salad dressing) that would result in consumption of raw or lightly cooked eggs.
 
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