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Diarrhea
Diarrhea is an increase in the frequency of bowel movements or a
decrease in the form of stool (greater looseness of stool). Although
changes in frequency of bowel movements and looseness of stools can
vary independently of each other, changes often occur in both.
Diarrhea needs to be distinguished from four other conditions. Although
these conditions may accompany diarrhea, they often have different
causes and different treatments than diarrhea. These other conditions are:
1. Incontinence of stool, which is the inability to control (delay) bowel
movements until an appropriate time, for example, until one can get to
the toilet
2. Rectal urgency, which is a sudden urge to have a bowel movement
that is so strong that if a toilet is not immediately available there will be
incontinence
3. Incomplete evacuation, which is a sensation that another bowel
movement is necessary soon after a bowel movement, yet there is
difficulty passing further stool the second time
4. Bowel movements immediately after eating a meal
Diarrhea can be defined in absolute or relative terms based on either the
frequency of bowel movements or the consistency (looseness) of stools.
Frequency of bowel movements. Absolute diarrhea is having more bowel
movements than normal. Thus, since among healthy individuals the
maximum number of daily bowel movements is approximately three,
diarrhea can be defined as any number of stools greater than three.
"Relative diarrhea" is having more bowel movements than usual. Thus, if
an individual who usually has one bowel movement each day begins to
have two bowel movements each day, then relative diarrhea is presenteven though there are not more than three bowel movements a day, that is,
there is not absolute diarrhea.
Consistency of stools. Absolute diarrhea is more difficult to define on the
basis of the consistency of stool because the consistency of stool can vary
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considerably in healthy individuals depending on their diets. Thus,
individuals who eat large amounts of vegetables will have looser stools
than individuals who eat few vegetables. Stools that are liquid or watery are
always abnormal and considered diarrheal. Relative diarrhea is easier to
define based on the consistency of stool. Thus, an individual who develops
looser stools than usual has relative diarrhea--even though the stools may
be within the range of normal with respect to consistency.
Why does diarrhea develop?
With diarrhea, stools usually are looser whether or not the frequency of
bowel movements is increased. This looseness of stool--which can vary all
the way from slightly soft to watery--is caused by increased water in the
stool. During normal digestion, food is kept liquid by the secretion of large
amounts of water by the stomach, upper small intestine, pancreas, and
gallbladder. Food that is not digested reaches the lower small intestine and
colon in liquid form. The lower small intestine and particularly the colon
absorb the water, turning the undigested food into a more-or-less solid
stool with form. Increased amounts of water in stool can occur if the
stomach and/or small intestine secretes too much fluid, the distal small
intestine and colon do not absorb enough water, or the undigested, liquid
food passes too quickly through the small intestine and colon for enough
water to be removed. Of course, more than one of these abnormal
processes may occur at the same time.
For example, some viruses, bacteria and parasites cause increased
secretion of fluid, either by invading and inflaming the lining of the small
intestine (inflammation stimulates the lining to secrete fluid) or by producing
toxins (chemicals) that also stimulate the lining to secrete fluid but without
causing inflammation. Inflammation of the small intestine and/or colon from
bacteria or from ileitis/colitis can increase the rapidity with which food
passes through the intestines, reducing the time that is available for
absorbing water. Conditions of the colon such as collagenous colitis may
block the ability of the colon to absorb water. Colitis means inflammation of
the colon. The colon, also known as the large intestine or large bowel,
constitutes the last part of the digestive tract. The colon is a long, muscular
tube that receives undigested food from the small intestine. It removes
water from the undigested food, stores the undigested food, and then
eliminates it from the body through bowel movements. The rectum is the
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last part of the colon adjacent to the anus. The common symptoms of colitis
include:

abdominal pain,

diarrhea, and

sometimes, rectal bleeding.
Diarrhea generally is divided into two types, acute and chronic.

Acute diarrhea lasts from a few days up to a week.

Chronic diarrhea can be defined in several ways but almost always
lasts more than three weeks.
It is important to distinguish between acute and chronic diarrhea because
they usually have different causes, require different diagnostic tests, and
require different treatment.
What are common causes of acute diarrhea?
The most common cause of acute diarrhea is infection--viral, bacterial, and
parasitic. Bacteria also can cause acute food poisoning. A third important
cause of acute diarrhea is starting a new medication.
Viral gastroenteritis
Viral gastroenteritis (viral infection of the stomach and the small intestine) is
the most common cause of acute diarrhea worldwide. Symptoms of viral
gastroenteritis (nausea, vomiting, abdominal cramps, and diarrhea)
typically last only 48-72 hrs. Unlike bacterial enterocolitis (bacterial infection
of the small intestine and colon), patients with viral gastroenteritis usually
do not have blood or pus in their stools and have little if any fever.
Viral gastroenteritis can occur in a sporadic form (in a single individual) or
in an epidemic form (among groups of individuals). Sporadic diarrhea
probably is caused by several different viruses and is believed to be spread
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by person-to-person contact. The most common cause of epidemic
diarrhea (for example, on cruise ships) is infection with a family of viruses
known as caliciviruses of which the genus norovirus is the most common
(for example, "Norwalk agent"). The caliciviruses are transmitted by food
that is contaminated by sick food-handlers or by person-to-person contact.
Food poisoning
Food poisoning is a brief illness that is caused by toxins produced by
bacteria. The toxins cause abdominal pain (cramps) and vomiting, and also
cause the small intestine to secrete large amounts of water that leads to
diarrhea. The symptoms of food poisoning usually last less than 24 hours.
With some bacteria, the toxins are produced in the food before it is eaten,
while with other bacteria, the toxins are produced in the intestine after the
food is eaten.
Symptoms usually appear within several hours when food poisoning is
caused by toxins that are formed in the food before it is eaten. It takes
longer for symptoms to develop when the toxins are formed in the intestine
(because it takes time for the bacteria to produce the toxins). Therefore, in
the latter case, symptoms usually appear after 7-15 hours.
Staphylococcus aureus is an example of a bacterium that produces toxins
in food before it is eaten. Typically, food contaminated with Staphylococcus
(such as salad, meat or sandwiches with mayonnaise) is left un-refrigerated
at room temperature overnight. The Staphylococcal bacteria multiply in the
food and produce toxins. Clostridium perfringens is an example of a
bacterium that multiplies in food (usually canned food), and produces toxins
in the small intestine after the contaminated food is eaten.
Traveler's diarrhea
There are many strains of E. coli bacteria. Most of the E. coli bacteria are
normal inhabitants of the small intestine and colon and are non-pathogenic,
meaning they do not cause disease in the intestines. Nevertheless, these
non-pathogenic E. coli can cause diseases if they spread outside of the
intestines, for example, into the urinary tract (where they cause bladder or
kidney infections) or into the blood stream (sepsis).
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Certain strains of E. coli, however, are pathogenic (meaning they can
cause disease in the small intestine and colon). These pathogenic strains
of E. coli cause diarrhea either by producing toxins (called enterotoxigeni
E. coli or ETEC) or by invading and inflaming the lining of the small
intestine and the colon and causing enterocolitis (called enteropathogenic
E. coli or EPEC). Traveler's diarrhea usually is caused by an ETEC strain
of E. coli that produces a diarrhea-inducing toxin.
Tourists visiting foreign countries with warm climates and poor sanitation
(Mexico, parts of Africa, etc.) can acquire ETEC by eating contaminated
foods such as fruits, vegetables, seafood, raw meat, water, and ice cubes.
Toxins produced by ETEC cause the sudden onset of diarrhea, abdominal
cramps, nausea, and sometimes vomiting. These symptoms usually occur
3-7 days after arrival in the foreign country and generally subside within 3
days. Occasionally, other bacteria or parasites can cause diarrhea in
travelers (for example, Shigella, Giardia, Campylobacter). Diarrhea caused
by these other organisms usually lasts longer than 3 days.
Bacterial enterocolitis
Disease-causing bacteria usually invade the small intestines and colon and
cause enterocolitis (inflammation of the small intestine and colon). Bacterial
enterocolitis is characterized by signs of inflammation (blood or pus in the
stool, fever) and abdominal pain and diarrhea. Campylobacter jejuni is the
most common bacterium that causes acute enterocolitis in the U.S. Other
bacteria that cause enterocolitis include Shigella, Salmonella, and EPEC.
These bacteria usually are acquired by drinking contaminated water or
eating contaminated foods such as vegetables, poultry, and dairy products.
Enterocolitis caused by the bacterium Clostridium difficile is unusual
because it often is caused by antibiotic treatment. Clostridium difficile is
also the most common nosocomial infection (infection acquired while in the
hospital) to cause diarrhea. Unfortunately, infection also is increasing
among individuals who have neither taken antibiotics nor been in the
hospital.
E. coli O157:H7 is a strain of E. coli that produces a toxin that causes
hemorrhagic enterocolitis (enterocolitis with bleeding). There was a famous
outbreak of hemorrhagic enterocolitis in the U.S. traced to contaminated
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ground beef in hamburgers (hence it is also called hamburger colitis).
Approximately 5% of patients infected with E. coli O157:H7, particularly
children, can develop hemolytic uremic syndrome (HUS), a syndrome that
can lead to kidney failure . Some evidence suggests that prolonged use of
anti-diarrhea agents or use of antibiotics may increase the chance of
developing HUS.
Parasites
Parasitic infections are not common causes of diarrhea in the U. S.
Infection with Giardia lamblia occurs among individuals who hike in the
mountains or travel abroad and is transmitted by contaminated drinking
water. Infection with Giardia usually is not associated with inflammation;
there is no blood or pus in the stool and little fever. Infection with amoeba
(amoebic dysentery) usually occurs during travel abroad to undeveloped
countries and is associated with signs of inflammation--blood or pus in the
stool and fever.
Cryptosporidium is a diarrhea-producing parasite that is spread by
contaminated water because it can survive chlorination. Cyclospora is a
diarrhea-producing parasite that has been associated with contaminated
raspberries from Guatemala.
What are common causes of chronic diarrhea?
Irritable bowel syndrome. The irritable bowel syndrome (IBS) is a
functional cause of diarrhea or constipation. Inflammation does not typically
exist in the affected bowel. (Nevertheless, recent information suggests that
there MAY be a component of inflammation in IBS.) It may be caused by
several different underlying problems, but it is believed that the most
common cause is rapid passage of the intestinal contents through the
colon.
Infectious diseases. There are a few infectious diseases that can cause
chronic diarrhea, for example, Giardia lamblia . Patients with AIDS often
have chronic infections of their intestines that cause diarrhea.
Bacterial overgrowth of the small intestine. Because of small intestinal
problems, normal colonic bacteria may spread from the colon and into the
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small intestine. When they do, they are in a position to digest food that the
small intestine has not had time to digest and absorb. The mechanism that
leads to the development of diarrhea in bacterial overgrowth is not clear.
Post-infectious. Following acute viral, bacterial or parasitic infections,
some individuals develop chronic diarrhea. The cause of this type of
diarrhea is not clear, but some of the individuals probably have bacterial
overgrowth of the small intestine. They also may have abnormalities, either
microscopic or biochemical, in biopsies of the intestines. This condition also
is referred to as post-infectious IBS.
Inflammatory bowel disease (IBD). Crohn's disease and ulcerative colitis,
diseases causing inflammation of the small intestine and/or colon,
commonly cause chronic diarrhea.
Colon cancer. Colon cancer can cause either diarrhea or constipation. If
the cancer blocks the passage of stool, it usually causes constipation.
Sometimes, however, there is secretion of water behind the blockage, and
liquid stool from behind the blockage leaks around the cancer and results in
diarrhea. Cancer, particularly in the distal part of the colon, can lead to thin
stools. The diarrhea or constipation caused by cancer usually is
progressive, that it becomes progressively worse. Cancer in the rectum can
lead to a sense of incomplete evacuation.
Severe constipation. By blocking the colon, hardened stool can lead to
the same problems as colon cancer, as discussed previously.
Carbohydrate (sugar) malabsorption. Carbohydrate or sugar
malabsorption is an inability to digest and absorb sugars. The most wellrecognized malabsorption of sugar occurs with lactase deficiency (also
known as lactose or milk intolerance) in which milk products containing the
milk sugar, lactose, lead to diarrhea. The lactose is not broken up in the
intestine because of the absence of an intestinal enzyme, lactase that
normally breaks up lactose into its component sugars, galactose and
glucose. Without being broken up, lactose cannot be absorbed into the
body. The undigested lactose reaches the colon and pulls water (by
osmosis) into the colon. This leads to diarrhea. Although lactose is the
most common form of sugar malabsorption, other sugars in the diet also
may cause diarrhea, including fructose and sorbitol.
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Fat malabsorption. Malabsorption of fat is the inability to digest or absorb
fat. Fat malabsorption may occur because of reduced pancreatic secretions
that are necessary for normal digestion of fat (for example, due to
pancreatitis or pancreatic cancer) or by diseases of the lining of the small
intestine that prevent the absorption of digested fat (for example, celiac
disease). Undigested fat enters the last part of the small intestine and colon
where bacteria turn it into substances (chemicals) that cause water to be
secreted by the small intestine and colon. Passage through the small
intestine and colon also may be more rapid when there is malabsorption of
fat.
Endocrine diseases. Several endocrine diseases (imbalances of
hormones) may cause diarrhea, for example, an over-active thyroid gland
(hyperthyroidism) and an under-active pituitary or adrenal gland (Addison's
disease).
Laxative abuse. The abuse of laxatives by individuals who want attention
or to lose weight is an occasional cause of chronic diarrhea.
What are the complications of diarrhea?
Dehydration occurs when there is excessive loss of fluids and minerals
(electrolytes) from the body due to diarrhea, with or without vomiting.
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Dehydration is common among adult patients with acute diarrhea who
have large amounts of stool, particularly when the intake of fluids is
limited by lethargy or is associated with nausea and vomiting.
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It also is common in infants and young children who develop viral
gastroenteritis or bacterial infection.
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Patients with mild dehydration may experience only thirst and dry
mouth.

Moderate to severe dehydration may cause orthostatic hypotension
with syncope (fainting upon standing due to a reduced volume of blood,
which causes a drop in blood pressure upon standing), a diminished
urine output, severe weakness, shock, kidney failure, confusion,
acidosis (too much acid in the blood), and coma.
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Electrolytes (minerals) also are lost with water when diarrhea is prolonged
or severe, and mineral or electrolyte deficiencies may occur. The most
common deficiencies occur with sodium and potassium. Abnormalities of
chloride and bicarbonate also may develop.
Finally, there may be irritation of the anus due to the frequent passage of
watery stool containing irritating substances.
When should the doctor be called for diarrhea?
Most episodes of diarrhea are mild and of short duration and do not need to
be brought to the attention of a doctor. The doctor should be consulted
when there is:
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High fever (temperature greater than 101 F)
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Moderate or severe abdominal pain or tenderness
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Bloody diarrhea that suggests severe intestinal inflammation
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Diarrhea in persons with serious underlying illness for whom
dehydration may have more serious consequences, for example,
persons with diabetes, heart disease, and AIDS
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Severe diarrhea that shows no improvement after 48 hours.
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Moderate or severe dehydration
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Prolonged vomiting that prevents intake of fluids orally
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Acute diarrhea in pregnant women because of concern for the health of
the fetus
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Diarrhea that occurs during or immediately after completing a course of
antibiotics because the diarrhea may represent antibiotic-associated
infection with C. difficile that requires treatment

Diarrhea after returning from developing countries or from camping in
the mountains because there may be infection with Giardia (for which
there is treatment)
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Diarrhea that develops in patients with chronic intestinal diseases such
as colitis, or Crohn's disease because the diarrhea may represent
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worsening of the underlying disease or a complication of the disease,
both requiring treatment

Acute diarrhea in an infant or young child in order to ensure the
appropriate use of oral liquids (type, amount, and rate), to prevent or
treat dehydration, and to prevent complications of inappropriate use of
liquids such as seizures and abnormal blood electrolytes

Chronic diarrhea