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How
Do Our Foods Become Contaminated Before Purchase?
In
the United States, there are a number of ways in which pathogenic
microbes can enter our food supply. Depending on the food,
the potential mechanisms for contamination vary. The sections
below include:
Beef,
Ground Beef, Venison, Lamb, Mutton and Beef-Related Salami
E.
coli O157:H7 bacteria reside in the intestinal tracts
of healthy cattle and other ruminants such as sheep and deer
and are excreted in their feces. As many as 63% of feedlots
have been found by a USDA Animal Production Food Safety study
from the summer of 1997 to have some cattle shedding O157:H7
at any point in time. When cattle are sent to the slaughter,
animals are sometimes left to fast for a day in order to clear
out their digestive systems.(3) This places them under greater
stress which is believed to result in a higher likelihood
of their shedding bacteria from their intestinal tracts. Often,
cattle are also confined in tight quarters on their way to
slaughter, increasing their stress levels and causing them
to excrete onto both themselves and other cattle.
When
the animal is slaughtered, the intestines can be accidentally
cut open, causing the intestinal contents to spill onto otherwise
uncontaminated muscle meat or the soiled hide of the animal
can come into contact with the muscle meat.
If
a piece of muscle meat is not penetrated (by being poked with
a fork, for example, for tenderizing), the pathogens on the
exterior of the muscle meat can be easily killed through reasonable
cooking at temperatures at or above 160 degrees and rendered
safe. However, if the muscle meat or its trimmings are fed
into a grinder, pathogens that were previously on the exterior
of the meat will then be ground and spread throughout the
interior of a batch of ground beef. In the case of O157:H7,
a potentially deadly bacteria more common to cattle and venison
than other food animals, the pathogen must be eliminated by
heating both the exterior AND the interior of the ground,
red meat to a temperature of 160 degrees throughout to eliminate
the danger. Cooking the meat until it is merely gray or brown
inside is not sufficient to ensure its safety.
If
only a single animal were involved in the production of hamburger,
the risk would be high enough. However, an existing practice
in the industry increases the likelihood of contamination
in a hamburger. Rather than take the trimmings and meat from
a single animal, often multiple animals may be combined in
a grinder. The meat of as many as a 100 cattle can be in a
single hamburger (4).Thus, uncontaminated animal meat can
become contaminated by infected animal meat when ground together.
If the ground meat is not processed in individual batches,
but continuously processed, the pathogens may be spread through
a large quantity of ground meat. Lastly, if the grinder is
not cleaned properly, the same effect may be achieved.
Consumers
should ask their ground meat suppliers the following questions:
- is
the ground meat processed on site or elsewhere?
- how
many animals went into it?
- from
how many different sources did the animals come?
- was
the ground meat batched or continuously processed?
- were
any other animal meats (such as pigs) ground with the same
equipment?
- how
large was each batch?
- how
frequently was the grinder cleaned?
- what
chemicals are used to sterilize it?
If
your meat supplier does not know the answers to these questions
or cannot get the answers for you, you may want to exercise
caution.
For
a long time, it was believed that the high acidity used
in "dry, cured" salami was enough to eliminate E.
coli O157:H7. A 1994 outbreak of salami in Seattle caused
by the San Francisco Sausage Company showed that previously
acceptable levels of acidity were not sufficient to kill
all
of the bacteria. In June 1998, Venetian Meat & Salami
Co. Ltd recalled many of its dry-cured meat products, including
salami, due to E. coli O157:H7 contamination.
Poultry
Salmonella
and Campylobacter are now common to United States poultry.
70 to 90% of chickens carry Campylobacter. (1) 20 to
80% of chickens carry Salmonella. (2) Typical grocery
store poultry is now raised in the United States under "intensive
farming" conditions. The birds are often kept in close
quarters such that they can come into contact with one another's
feces. Birds can be contaminated by other birds in transit
to the slaughterhouse. When they are shipped to slaughter,
their pens may not be disinfected before new birds are moved
in, thus allowing previously infected poultry to infect a
new "batch."
Once
birds are killed, the feathers are removed with mechanized
fingers which can move organisms from the feathers onto
the
carcass. As described in Nicols Fox' book, "Spoiled,"
"After
the chicken is 'vented' (opened), it is gutted, also
by
machine. A metal hook reaches up inside the bird and pulls
out the intestines. The trouble is, there are going to
be
variations even among chickens of almost exactly the same
size... Often the intestines break and the contaminated
contents spill out. These birds should be removed from
the
process, but often they are not. On they go, contaminating
other birds along the way. The chickens are rinsed twice
more, but then they are dragged through a bath of chill
water, where they remain for an hour... A USDA study
revealed
that at one federally inspected slaughter establishment
58 percent of the chickens were contaminated with Salmonella before
they were eviscerated. That dropped to 48 percent after
the two washes. But after an hour in the chill water,
contamination increased to 72 percent."
According
to Fox, the poultry spend so much time in the chill bath because
it adds water weight to the chicken. USDA allows poultry to
gain 8% of bird weight in water.
Eggs
Shell
eggs are now known to become internally contaminated when
the hen laying them develops an infection of Salmonella in
its ovaries. Examples of foods that may contain undercooked
eggs are: Hollandaise sauce, Bernaise sauce, timbales, eggs
- sunny side up, eggs - soft boiled, Ice creams, some homemade
frostings, eggnog, tartar sauce, mayonnaise, meringue, mousse,
soufflés, and fresh Caesar salad dressings.
Seafood
Shellfish
such as clams and oysters get their nutrients by filtering "food" from
the water in which they live. Norwalk virus and other illnesses
comes from human feces entering
the water either via boaters using the water as a toilet
or via sewage lines emptying into the water. A naturally
occurring
bacteria, Vibrio vulnificus, grows in coastal waters
around the world, particularly during warm weather months.
After
harvesting shellfish from the ocean, the shellstock are
frequently
kept at "air temperature," which can be very warm
and encourage bacterial growth, though they are often harvested
with an already high bacterial load.
In
general, raw seafood such as fish is susceptible to infection
from parasites such as Toxoplasmosis protozoa.
Produce
While
it might seem strange that fruit and vegetables would come
in contact with the human and animal feces that often harbors
pathogenic bacteria, there are many routes by which this can
happen. Wild animals whether small, such as rodents or birds,
or large such as deer, can often gain access to a farm or
orchard during the growing season and can contaminated produce
with their feces and even other animals' feces with which
they've come into contact. The water with which produce comes
into contact while growing should be clean; yet, well water
or nearby streams can become contaminated and rainwater runoff
can bring contamination from land higher up, thereby contaminating
the crops. Lastly, the application of manure from cattle or
poultry can easily introduce pathogens. There are no federal
rules or regulations regarding the use of fresh manure as
a fertilizer for produce. As of February, 1998, voluntary
organic standards for delaying the application of raw manure
recommended not applying it within 60 days of harvest. Yet,
E. coli O157:H7 and Salmonella have been shown
to survive for many months in soil.
The
location of the farm or orchard or processing facilities near
other farm animals can also result in contamination. It is
believed that some bacteria can form spores and be blown in
dust onto nearby produce or into water used for rinsing. Birds,
as well, have been know to carry pathogens such as Campylobacter
and E. coli O157:H7, so proximity can be an issue.
Harvesting
introduces the human element. Unclean hands can contaminate
fresh produce with human pathogens such as hepatitis A. Workers
can walk through contaminated dirt and climb up ladders placing
their hands on rungs they have just soiled. Often, workers
sit on their picking bags while taking a break. Baskets are
placed on the ground and can easily get contaminated soil
in them. Thus, previously pristine produce can be subsequently
contaminated during harvest.
The
processing facility itself can be left open to contamination
from dust or animals. Dirt floors can contribute to the risk
of contamination. In the processing shed, produce can be rinsed
with unclean water, whether contaminated by dust or animals
or previous produce passing through the process. Tools such
as filters, knives or fingernails may not be sterilized between
processes or may left in a place where they can again become
contaminated via dust, nonpotable water or animals. A part
may fall on the floor, be picked up and put back into the
process again without being properly cleaned. Lastly, the
final packaging materials, cartons, etc. can be contaminated
by previous fruit or tainted water, by being set on contaminated
ground tainted by manure, or by being transported in a vehicle
that previously held animals.
Alfalfa
Sprouts
As
long as they weren't grown in raw manure, you might think
sprouts would be a relatively safe form of produce. After
all, they can be grown effectively indoors. Yet indoor growing
conditions of sprouts can be substantially less than sanitary.
Epidemiology points to the source of at least one outbreak
as being the seed itself. How would alfalfa seed become contaminated?
Alfalfa as a crop can be fertilized with raw manure. A combine
is then used to harvest the grass and seed, whipping up a
considerable amount of the soil in the process of harvesting.
Thus, a seed which might otherwise not have come into contact
with animal feces, could easily become contaminated.
The
challenge with sprouts is that the growing conditions that
foster sprout growth are ideal for escalated bacterial
growth.
For approximately 3 days, sprout seeds are warmed, kept moist
and given a lot of light in order to encourage growth.
If
contaminated seed comes into a sprout growing facility it
can enable an organism to "set up shop" in a
location within the facility, thereby enabling multiple
batches to
be contaminated. Thus, even with a process that reduces contamination
in seed, if contamination is not completely eliminated,
the
odds of growth of potentially deadly organisms is high. For
reasons similar to these, the FDA and California Department
of Health Services have recommended that at-risk consumers,
including children, the elderly and the immune impaired
not
eat alfalfa sprouts. Note that mung beans sprouts, which
are most often served cooked, and radish sprouts have also
been
sources of outbreaks.
Juice
Contamination
in fresh juice can result from contamination of the fruit
itself as described above under "Produce." However,
the combination of multiple pieces of fruit into a single
batch of juice increases the likelihood of contamination.
If a single piece of fruit is contaminated and is mashed into
a batch of 100 other pieces of uncontaminated fruit, then
the juice of all will be contaminated. As with the processing
of ground meat, if the juice is "continuously" processed
or equipment is not sufficiently cleaned between batches,
a single piece of fruit can contaminate multiple batches.
(1)
Boodman, Sandra G.; "Poultry Peril: What Is Campylobacter and
Why Is It the Leading Cause of Food Poisoning," 12/9/97,
Washington Post
(2)
Fox, Nicols, "Spoiled," Basic Books, 1997.
(3)
Fox, Nicols, "Spoiled," Basic Books, 1997, Page
261.
(4)
Robert Tauxe, quoted in Fox, Nichols, "Spoiled," Basic
Books, 1997.
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