Frequently Asked Questions
Salmonella
enteritidis Infection
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.
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.
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.
Reducing the risk of Salmonella enteritidis infection
- 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. Do not keep eggs warm for
more than 2hours.
- Refrigerate unused or leftover egg- containing foods.
- 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.
- 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.
What
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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