Information for Dietitians and Health Professionals
Introduction
Historically food safety issues were the responsibility of each individual.
As society became more industrialized the safety of food production, preparation
and consumption became more of a concern. At the beginning of the twentieth
century, lack of scientific knowledge and food industry guidance led to outbreaks
of foodborne illness all over the world.
With the advent of more advanced scientific
and medical knowledge as well as technological advancement,
foodborne pathogens were isolated and techniques for preventing
food contamination were developed. Understanding and communicating
safe food practices is now known to be essential to the
continued health of our entire society.
For the consumer, food safety involves
prudent food purchases, sanitary food preparation and safe
food preservation. Old world traditions and unsafe, unscientific
practices need to be corrected before acceptance of modern
methods can be assured. Knowing the populations at greatest
risk for foodborne illness can help target the message
that food safety must be taken seriously.
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Risk
Factors
The importance of food safety in our modern world is ever increasing. The growth
of the population of Americans over the age of 65 years means health professionals
need to be aware of loss of consumer's natural defenses. As part of the aging
process, diminished sight, smell and taste can fail to warn seniors of spoiled,
unsafe foods. Reduced stomach acid production often related to aging, reduces
the defenses needed to protect the mature adult from contaminated food. Slower
immune response also may make seniors more vulnerable to the spread of infection.
Children are also at greater risk for
foodborne illness due to their immature immune system.
They may require greater supervision due to their lack
of education and their natural interest in exploring their
environment, often involving unsafe food practices. Pregnant
women also are at greater risk due to immaturity of defense
system in the developing fetus.
Persons that are immune compromised due
to medical treatment or disease are at greater risk for
foodborne illness. They may be unable to defend themselves
from the spread of infection once introduced into their
body.
Of concern for the general population
is the threat of foodborne illness due to a changed environment.
With increased workloads and less time devoted to food
purchasing and preparation, many more people are turning
to foods prepared outside the home. Due to increased demand,
more of the food industry has become centralized in its
production, preparation and distribution leading to a greater
chance of widespread contamination.
Pathogens are constantly changing to adapt
to new environments and are becoming more difficult to
detect and treat. With the globalization of society, we
now come into contact with pathogens that had remained
localized in the past. Food trends also
may increase the risk of foodborne illness. Recent interest
in natural, organic, raw and untreated foods can lead to
more risky food consumption. For these reasons, it is ever
more important to prevent foodborne illness by following
safe food practices, before the pathogens are allowed to
multiply.
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Organisms
of Foodborne Illness
Bacteria, virus and fungi can cause foodborne illness. These organisms can
cause health problems by either infection, where the organism enters the intestine
of the host and begins multiplying, or by intoxication where the organism begins
to produce a toxin or poison in the food that is harmful to the consumer.
Examples of bacteria that infect their
host through contact with food are Listeria monocytogenes, Salmonella spp
and Escherichia coli 0157:H7. Bacteria that are
known to produce toxins in foods that can harm the consumer
are Clostridium botulinum, Staphylococcus aureus and Bacillus
cereus.
Listeria monocytogenes is most
often associated with unpasteurized milk and cheese, ice
cream, raw vegetables, poultry, meats and seafood. It can
be found also in chilled ready to eat foods made from these
products. Symptoms in humans infected with this foodborne
illness include nausea, vomiting, diarrhea, fever, and
spontaneous abortion or stillbirth in pregnant women. Incubation
period for illness is from three to seventy days, usually
about three weeks. Preventative measures include using
pasteurized milk and dairy products, cooking foods to proper
temperature, clean surfaces and avoidance of cross contamination.
Salmonella species are most often
associated with poultry and poultry salads, meat and meat
products, fish, shrimp, milk, shell eggs, egg products,
tofu, and fresh produce. The incubation period for illness
is from six to forty eight hours, usually between twelve
and thirty six hours. Preventative measures include avoidance
of cross contamination, refrigeration of foods, thorough
cooking of poultry to 165°F for at least 15 seconds and
good personal hygiene practices.
Salmonella enterica serotype Enteritidis
commonly referred to as SE is the dominant organism of
concern with regard to food safety from poultry sources.
SE is of particular interest to the egg industry because
SE can infect the reproductive organs of egg laying hens.
Eggs can be contaminated if the hens are infected and SE
may be deposited in or on the egg.The hen shows no sign
of infection, and the egg appears to be normal. The rate
of egg contamination with SE is sporadic, with estimates
ranging from as little as one egg in twenty thousand eggs
(0.005%) to one in ten thousand eggs (0.01%). The prevalence
of SE has been declining in the U.S. due to government
and industry programs that reduce the risk of spreading
SE infection. These programs focus on producer actions
that require thorough cleaning and disinfecting of layer
houses between flocks, good rodent control techniques,
and proper refrigeration of eggs.
Escherichia coli is most often
associated with raw and undercooked ground beef, imported
cheese, unpasteurized milk and apple cider, dry salami,
roast beef, lettuce and nonchlorinated (untreated) water.
There are many types of coliforms, most of which are found
naturally in the gastrointestinal system.E. coli O157:H7 is
the most dangerous form of the bacteria and is infective
in very small doses. Incubation period for illness is from
three to eight days usually three to four days. Preventative
measures include thorough cooking of ground beef to at
least 155°F for 15 seconds, avoidance of cross contamination
and good personal hygiene.
Clostridium botulinum is most often
associated with foods that are underprocessed or temperature
abused in storage, canned low acid foods, home canned foods,
leftover baked potatoes, stews, and meat or poultry loaves.
C. botulinum grows in anaerobic environments. C. botulinum produces
a neurological toxin that causes botulism in humans. The
incubation period is four to eight days, usually twelve
to thirty six hours. Preventative measures include avoidance
of home canned foods, rapidly cooling leftovers and using
careful time and temperature control of food products.
Commercially canned foods have been treated to inactivate Clostridium
botulinum.
Staphylococcus aureus is most often
associated with reheated foods, ham and other meats, poultry
and other protein foods, milk and dairy products and potato
salad, custards, cream filled pastries and salad dressing.
Incubation period is from one to seven hours usually two
to four hours. Preventative measures include good personal
hygiene including avoidance of contact with unwashed hands,
avoidance of food contact by persons with skin infection,
proper refrigeration and cooking of prepared foods. Many
people are carriers of Staphyloccus
aureus and are unaware. The bacteria is harmless until
it has contact with food and has the nutrients to multiply
and a toxin is produced. Good hygiene, including hand washing,
is the most important preventative factor.
Bacillus cereus is most often associated
with rice products and starchy foods, sauces, pudding,
soups, casseroles, pastries, salads, meats, milk, vegetables
and fish. Incubation period is thirty minutes to
six hours or six to fifteen hours depending on route of
symptom. Preventative measures include careful time and
temperature control as well as quick chilling and adequate
cooking of food.
Nearly all the foodborne illnesses cited
above first appear as similar symptoms. Common symptoms
include nausea, vomiting, diarrhea, headaches and fever.
Generally, the duration of foodborne illness is less than
a week. Some may progress to more severe symptoms such
as Clostrium
botulinum that can cause eventual paralysis and death.
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Natural
Design Protective Qualities in Egg
It is important to remember that an egg has many natural barriers to prevent
bacterial growth. These barriers include the shell, the membranes within the
shell and the egg white itself.
Eggs are laid with a natural protective
coating on the shell that is removed when the eggs are
washed and replaced with a coating of mineral oil before
the eggs are packed.The inner shell membrane is made of
nonporous protein fibers that contain lysozyme, a substance
that naturally protects against bacterial invasion. The
outer white layer is alkaline and therefore an unfavorable
medium for bacterial growth. In addition, nutrients required
to support bacterial growth are absent from the outer white
layer.
The thick white surrounding the yolk is
also alkaline, and in addition to lysozyme it contains
conalbumin and ovatransferrin that bind iron and other
metals. Also found in the egg white is avidin that binds
biotin and flavoprotein which binds riboflavin, making
these nutrients unavailable to bacteria or humans until
the egg white is cooked. The viscosity of the egg white
can contribute to the immobilization of bacteria and anaerobic
conditions that discourage bacterial growth.
The chalaziferous layer of the white,
just before the yolk, is very dense. It contains little
of the water which bacteria need, but a high concentration
of all the thick white's protective materials. The thick,
ropey egg white strands, called chalazae, hold the yolk
centered in the egg where it receives maximum protection
from all the other layers. A prominent chalazae is a sign
of a fresh egg.
As the egg ages and the white thins, the
yolk membrane becomes more permeable and bacteria can,
if given the right time and temperatures, reach the nutrient
dense yolk and begin to grow. To ensure that eggs remain
safe to consume, proper handling, cooking and storage procedures
are of utmost importance.
The vast majority of reported cases of
foodborne illness associated with eggs or foods containing
eggs have involved improper handling procedures, inadequate
refrigeration and undercooking.
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Food
Safety Regulation of Shell Eggs
Eggs are regulated by both the Food and Drug Administration (FDA) www.fda.gov and the US Department of Agriculture (USDA) www.usda.gov.The USDA administers a voluntary grading program for shell eggs through the Agricultural Marketing Service (AMS) www.ams.usda.gov/
Shell eggs are regulated by the FDA.In
December 2000, the FDA issued two new rules for shell eggs,
one for refrigeration and one for labeling eggs with safe
handling instructions. In September of 2004, the FDA
published a proposed rule "Prevention of Salmonella
Enteritidis in Shell Eggs During Production". The
FDA has stated that they plan to publish a final rule in
their fiscal year 2006.
In shell pasteurization of eggs has been
approved by the Food and Drug Administration and is available
for use by consumers, hospitals and nursing homes where
consumers of highest risk reside. The FDA has most recently
approved the use of irradiation in shell eggs. Eggs now
join a growing list of foods permitted to utilize irradiation
to reduce the risk of foodborne illness. Irradiation has
previously been approved for use on raw meat and meat products,
poultry, fruits, vegetables, flour and spices. Irradiation
using the maximum of three kilgrays of ionizing radiation
has been found to cause only minimal changes in protein,
lipid and carbohydrate levels of fresh eggs and has been
determined by FDA to not differ in any significant manner
from non-irradiated eggs.
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Food
Safety Regulation of Egg Products
Egg products are regulated under the Egg Products Inspection Act of 1970 (EPIA).
The EPIA assures that all egg products undergo continuous inspection and are
pasteurized. Examples of egg products are whole liquid eggs, liquid whites,
yolks, and all frozen and dried egg products. Basically, once an egg is broken
by an egg processor, it falls under the EPIA and must be pasteurized. The USDA's
Food Safety and Inspection Service www.fsis.usda.gov/ is
responsible for inspecting egg products.
Most egg products are used by food manufacturers
and food service institutions. Some companies are
starting to offer different egg products to consumers at
retail stores, such as dried egg whites, and whole liquid
egg.
Since egg products are pasteurized based
on temperature and time requirements to destroy Salmonella
in eggs, they are safe to consume raw or undercooked. However,
once the original package is open, the shelf life of liquid
and frozen products is very short. Egg products should
be refrigerated properly and handled with the same care
as shell eggs.
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