FOOD POISONING
F
FOOD POISONING
Some animals, including cows, pigs, poultry, and shellfish,
harbour disease organisms (such as bacteria, viruses, worms,
and parasites) in their tissues; these organisms may cause
infection if meat, fish, or dairy products are consumed raw or
are improperly cooked. Beef, pork, and fish tapeworm
infestations, salmonella poisoning, and (rarely) brucellosis
can be transmitted in this way. Adequate pasteurization of
milk and the inspection of meat and fish before they go on
sale prevent most infections and infestations of this type from
occurring. Thorough preparation and cooking of meat, fish,
shellfish, poultry, and eggs further reduce the risk of infection.
FOOD CONTAMINATION
Intestinal infections may be spread from person to
person if organisms in faeces contaminate food,
either directly or indirectly. Contamination can occur if
vegetable crops are sprayed with sewage, if flies settle
on faeces and then on food, or if food is handled by a
person who has not washed his or her hands.
Contaminating organism
The photograph (left),
taken through an electron
microscope, shows a
typical
S a l m o n e l l a
bacterium. The organism
uses its manyflagellae
(whiplike structures) to
move.
S a l m o n e l l a
is a
common contaminant of
poultry, eggs, and egg
products and may cause
severe food poisoning.
food poisoning:
and it does not involve
the
immune system.
Food intolerance
is commonly
of
unknown cause. Certain foods may be
poorly tolerated as a result of impaired
digestion and absorption, w hich may
be associated with
disorders of the
pancreas
or of the
biliary system
(w hich
produce digestive juices to break down
food). Some individuals have a genetic
deficiency of a specific
enzyme,
such
as
lactase
(w hich is required for the
digestion
of lactose,
the
sugar that
occurs
in
m ilk);
on drinking
milk,
those people with lactose intolerance
develop abdominal cramps, flatulence,
and loose stools.
food poisoning
A term used to describe any gastro-
intestinal illness of sudden onset that is
likely to have been caused by contami-
nated food or water. Most cases of food
poisoning are caused by contamination
of food or water by bacteria, viruses,
or parasites. The illness is more com-
mon in hot weather.
Food poisoning is usually suspected
when, for example, several members
of a household (or customers at a par-
ticular
restaurant)
become
ill
after
eating the same food.
BACTERIAL CAUSES
The bacteria commonly responsible for
food poisoning belong to the groups
S
a l m o n e l l a
,
C A M P Y L O B A C T E R
, and E.
c o
n,
certain strains of w hich are capable of
m ultiplying rapidly in the intestines to
cause widespread inflammation. Food
poisoning may also be caused by L
i s t e r i a
(see
listeriosis).
Certain farm animals, especially poul-
try, commonly harbour the bacteria that
are responsible for food poisoning. If
frozen poultry is incompletely thawed
before
being
cooked,
or
if
it
is
not cooked thoroughly, it is liable to
cause
food poisoning.
Eggs
laid
by
affected poultry may also contain dis-
ease-causing bacteria. Fresh eggs are
unlikely to be heavily contaminated,
However, but eggs that are kept for
more than a couple of weeks should be
thoroughly cooked before being eaten.
Bacteria may also be transferred to food
from the excrement of infected animals
or people; the bacteria can be transmit-
ted either by flies or through poor
personal hygiene.
Some types
of bacteria
cause the
formation of toxins, w hich may be dif-
ficult to destroy even after thorough
cooking.
For
example,
the
organism
C
l o s t r i d i u m
p e r f r i n g e n s
is resistant
to
heat, and it may survive in precooked
foods, such as pies,
that have been
incorrectly stored.
Botulism
is an un-
common, life-threatening form of food
poisoning that is caused by a bacterial
toxin. The foods most likely to cause
botulism
are
home-preserved
fruit,
vegetables, and fish.
VIRAL CAUSES
The viruses that are most commonly
responsible
for
food
poisoning
are
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