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Egg
Associated Salmonellosis
Egg-associated
salmonellosis is an important public health problem
in the United States and several European countries. A bacterium, Salmonella
enteritidis,
can be inside perfectly normal-appearing eggs, and if the eggs are
eaten raw or undercooked, the bacterium can cause illness. During the
1980s, illness related to contaminated eggs occurred most frequently in
the northeastern United States, but now illness caused by S.
enteritidis
is increasing in other parts of the country as well. Consumers should
be aware of the disease and learn how to minimize the chances of
becoming ill.
A person infected with the Salmonella enteritidis
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.
How
eggs become contaminated
Unlike
eggborne salmonellosis of past decades, the current epidemic is due to
intact and disinfected grade A eggs. Salmonella enteritidis
silently infects the ovaries of healthy appearing hens and contaminates
the eggs before the shells are formed.
Most
types of Salmonella
live in the intestinal tracts of animals and birds and are transmitted
to humans by contaminated foods of animal origin. Stringent procedures
for cleaning and inspecting eggs were implemented in the 1970s and have
made salmonellosis caused by external fecal contamination of egg shells
extremely rare. However, unlike eggborne salmonellosis of past decades,
the current epidemic is due to intact and disinfected grade A eggs. The
reason for this is that Salmonella enteritidis silently infects
the ovaries of healthy appearing hens and contaminates the eggs before
the shells are formed.
Although
most infected hens have been found in the northeastern United States,
the infection also occurs in hens in other areas of the country. In the
Northeast, approximately one in 10,000 eggs may be internally
contaminated. In other parts of the United States, contaminated eggs
appear less common. Only a small number of hens seem to be infected at
any given time, and an infected hen can lay many normal eggs while only
occasionally laying an egg contaminated with the Salmonella bacterium.
Who can be infected?
The
elderly, infants, and persons with impaired immune systems are at
increased risk for serious illness.
Healthy
adults and children are at risk for egg-associated salmonellosis, 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. Most
of the deaths caused by Salmonella
enteritidis
have occurred among the elderly in nursing homes. Egg-containing dishes
prepared for any of these high-risk persons in hospitals, in nursing
homes, in restaurants, or at home should be thoroughly cooked and
served promptly.
Reducing the risk of Salmonella enteritidis infection
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Keep eggs refrigerated. |
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Discard
cracked or dirty eggs. |
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Wash
hands and cooking utensils with soap and water after contact with raw
eggs. |
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Eat
eggs promptly after cooking. Do not keep eggs warm for more than
2hours. |
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Refrigerate
unused or leftover egg- containing foods. |
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Avoid
eating raw eggs (as in homemade ice cream or eggnog). Commercially
manufactured ice cream and eggnog are made with pasteurized eggs and
have not been linked with Salmonella enteritidis infections. |
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Avoid
restaurant dishes made with raw or undercooked, unpasteurized eggs.
Restaurants should use pasteurized eggs in any recipe (such as
Hollandaise sauce or caesar salad dressing) that calls for pooling of
raw eggs. |
Related Links:
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What
is the risk?
In
affected parts of the United States, we estimate that one in 50 average
consumers could be exposed to a contaminated egg each year. If that egg
is thoroughly cooked, the Salmonella organisms will be
destroyed and will not make the person sick. Many dishes made in
restaurants or commercial or institutional kitchens, however, are made
from pooled eggs. If 500 eggs are pooled, one batch in 20 will be
contaminated and everyone who eats eggs from that batch is at risk. A
healthy person's risk for infection by Salmonella enteritidis
is low, even in the northeastern United States, if individually
prepared eggs are properly cooked, or foods are made from pasteurized
eggs.
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What
you can do
to
reduce risk
Eggs,
like meat, poultry, 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. The larger
the number of Salmonella present in the egg, the more likely it
is to cause illness. Keeping eggs adequately refrigerated prevents any Salmonella
present in the eggs from growing to higher numbers, so eggs should be
held refrigerated until they are needed. Cooking reduces the number of
bacteria present in an egg; however, an egg with a runny yolk still
poses a greater risk than a completely cooked egg. Undercooked egg
whites and yolks have been associated with outbreaks of Salmonella
enteritidis infections. Both should be consumed promptly and not be
held in the temperature range of 40 to 140
for more than 2 hours.
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else is being done?
Government agencies and the
egg industry have taken steps to reduce Salmonella enteritidis
outbreaks. These steps include the difficult task of identifying and
removing infected flocks from the egg supply and increasing quality
assurance and sanitation measures.
The
Centers for Disease Control has advised state health departments,
hospitals, and nursing homes of specific measures to reduce Salmonella
enteritidis
infection. Some states now require refrigeration of eggs from the
producer to the consumer. The U.S. Department of Agriculture is testing
the breeder flocks that produce egg-laying chickens to ensure that they
are free of Salmonella enteritidis. Eggs from known infected
commercial flocks will be pasteurized instead of being sold as grade A
shell eggs. The U.S. Food and Drug Administration has issued guidelines
for handling eggs in retail food establishments and will be monitoring
infection in laying hens.
Research by these agencies
and the egg industry is addressing the many unanswered questions about Salmonella
enteritidis,
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.
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