and failure of food handlers to wash their hands.
Restaurants are inspected by local health authorities.
Home preparation: letting food sit out too long at
room temperature, inadequate cooking, cross-
contamination between cooked and raw food, failure
to properly reheat leftoversBacteria
Bacterial contamination is the leading cause of
food poisoning. At room temperature, bacteria repro-
duce at astounding rates. A single bacterium that
divides every half hour can produce 17 million offspring
in 12 hours. Bacteria fall into two general categories.
One group causes symptoms of food poisoning by
directly infecting the intestines causing irritation and
diarrhea. The other group release toxins (poisons) as
they grow and reproduce. These toxins affect the diges-
tive system and often cause vomiting first followed by
diarrhea. Many bacteria cause food poisoning. A few of
the more common ones are described below.
Bacteria of the genusSalmonellaare common in
reptiles, birds, and mammals. They are found most
often in eggs, poultry, dairy products, and beef. Infec-
tion withSalmonellacauses nausea, vomiting, stomach
cramps, headache, and low-grade fever. Symptoms
begin anywhere from 6 to 48 hours after exposure and
may last for 7 days. In people with weakened immune
systems,Salmonella
Bacteria of the genusCampylobactercause more
diarrhea illnesses worldwide than any other group of
bacteria. They produce fairly mild diarrhea, fever,
and stomach cramps. Campylobacter bacteria are
found in almost all raw chicken and turkey. Cross-
contamination, that is putting cooked food down where
raw food had been, is a leading cause of food poisoning
fromCampylobacter. These bacteria are also transmitted
by water contaminated with animal feces.
Escherichia coliare a large group of bacteria, only
some of which cause food poisoning.E. colifood
poisoning usually begins with watery diarrhea that
later turns bloody. One strain ofE. coliknown as
0157:H7 is most often found in undercooked ham-
burger, but has also been found in ready-to-eat rawspinach. This particular strain can cause kidney failure
and death, especially in children and the elderly.
Clostridium botuliniumis a bacteria that causes the
disease botulism.C. botuliniumproduces a toxin that
affects the nervous system and can cause difficulty
breathing and paralysis. Symptoms do not appear
until 1 to 4 days after exposure. Botulism is associated
with improperly canned food, smoked fish, and honey.
Infection withC. botuliniumis serious and often fatal.Viruses
A large group of viruses called Norwalk or Nor-
walk-like viruses are an extremely common cause of
foodborne illness. In the mid-2000s, Norwalk viruses
were often in the news for causing outbreaks of gastro-
intestinal disease on cruise ships and in nursing homes.
They cause more vomiting than diarrhea than any
other viruses. Unlike many of the other causes of
food poisoning, these viruses are not usually naturally
present in food. They are usually transferred from the
hands of infected food handlers to the food that they
are preparing, especially to foods such as salads and
sandwiches.Parasites
Parasites that cause food poisoning usually come
from contaminated water. They often cause mild symp-
toms that are slow to develop but last for several weeks.
Giardiacauses watery diarrhea and is often acquired by
drinking untreated water from lakes or streams.
Cyrptosporidiumis a parasite that causes large amounts
of watery diarrhea for 3–4 days. Healthy people usually
recover quickly, but in people with weakened immune
systems, symptoms can persist for a long time.Natural toxins
Natural poisons found in some wild mushrooms
can cause anything from nausea and vomiting to hal-
lucinations, coma, and death, depending on the
amount and species of mushroom eaten. Mushroom
poisoning is a medical emergency. People who believe
they have eaten a poisonous mushroom should, if
possible, take a sample of the mushroom or their
vomit to the emergency room with them. Identifying
the type of mushroom causing the illness can help
determine the most effective treatment.
Oysters, clams, mollusks, and scallops can contain
toxins that affect the nervous system. Symptoms usu-
ally begin with a tingling in the mouth, then the arms
and legs. Individuals may become dizzy and may have
difficulty breathing. Shellfish poisoning is a medical
emergency because the muscles needed for breathingKEY TERMS
Pathogen—An organism that causes a disease.
Toxin—A general term for something that harms or
poisons the body.
Food poisoning