C h a p t e r 2 9
Disorders of Gastrointestinal Function
711
6 weeks.
36
In most cases systemic manifestations are
absent and the symptoms subside after the antibiotic
has been discontinued. A more severe form of coli-
tis, pseudomembranous colitis,
is characterized by an
adherent inflammatory membrane overlying the areas of
mucosal injury. It is a life-threatening form of the disease.
Persons with the disease are acutely ill, with lethargy,
fever, tachycardia, abdominal pain and distention, and
dehydration. The smooth muscle tone of the colon may
be lost, resulting in toxic dilation of the colon. Prompt
therapy is needed to prevent perforation of the bowel.
The diagnosis of
C. difficile
colitis requires a care-
ful history, with particular emphasis on antibiotic use.
Diagnostic findings include a history of antibiotic use
and laboratory tests that confirm the presence of
C.
difficile
toxins in the stool.
33,34
Patients with
C. diffi-
cile
infection should be put on contact precautions and
placed in a single room with a bathroom or, if unavail-
able, with other infected patients.
35
Treatment includes the immediate discontinuation
of antibiotic therapy. Specific treatment aimed at eradi-
cating
C. difficile
is used when symptoms are severe or
persistent. Metronidazole is the drug of first choice,
with vancomycin being reserved for persons who can-
not tolerate metronidazole or do not respond to the
drug. Both drugs are given orally.
33,34
Metronidazole is
absorbed from the upper gastrointestinal tract and may
cause side effects. Vancomycin is poorly absorbed, and
its actions are limited to the gastrointestinal tract.
Escherichia coli O157:H7 Infection.
Enterohemor
rhagic
E. coli
O157:H7 has become recognized as an
important cause of epidemic and sporadic colitis.
6
E. coli
O157:H7 is a strain of
E. coli
found in the feces and
contaminated milk of healthy dairy and beef cattle, but
it also has been found in contaminated pork, poultry,
and lamb. Infection usually is by food-borne transmis-
sion, often by ingesting undercooked ground beef. The
organism also can be transferred to nonmeat products
such as fruits and vegetables. Transmission has also
been reported in persons swimming in a fecally con-
taminated lake as well as among visitors to farms and
petting zoos who are in direct contact with animals.
Person-to-person transmission may occur, particularly
in nursing homes, day care settings, and hospitals. The
very young and the very old are particularly at risk for
the infection and its complications.
Although most strains of
E. coli
are harmless,
E. coli
0157:H7 produce
Shigella
-like toxins that attach to
and damage the mucosal lining of the intestine, caus-
ing bloody diarrhea.
6,36,37
Subsequently, the
Shigella
-like
toxins gain access to the circulatory system, where they
damage the endothelium and initiate platelet activation.
Two complications of the infection, hemolytic uremic
syndrome and thrombotic thrombocytopenic purpura,
reflect the effects of the
Shigella
-like toxins. The hemo-
lytic uremic syndrome is characterized by hemolytic
anemia, thrombocytopenia, and renal failure caused by
platelet thrombi in the renal microvasculature. It occurs
predominantly in infants and young children and is the
most common cause of acute renal failure in children.
It has a mortality rate of 3% to 5%, and one third of the
survivors are left with permanent disability. Thrombotic
thrombocytopenic purpura is manifested by thrombocy-
topenia, renal failure, fever, and neurologic manifesta-
tions caused by microthrombi in the brain.
No specific therapy is available for
E. coli
O157:H7
infection. Treatment is largely symptomatic and directed
toward treating the effects of complications. The use of
antibiotics or antidiarrheal agents in the early stages of
diarrhea has been shown to increase the risk of hemo-
lytic uremic syndrome because the gut is exposed to a
greater amount of toxins for a longer time. Because of
the seriousness of the infection and its complications,
education of the public about techniques for decreas-
ing primary transmission of the infection from animal
sources is important. Undercooked meats and unpas-
teurized milk are sources of transmission. Food handlers
and consumers should be aware of the proper methods
for handling uncooked meat to prevent cross-contam-
ination of other foods. Particular attention should be
paid to hygiene in day care centers and nursing homes,
where the spread of infection to the very young and very
old may result in severe complications.
Diverticular Disease
Diverticulosis is a disorder characterized by pseudodi-
verticula of the colonic mucosa and submucosa.
6,7,38–40
Although the disorder is prevalent in the developed
countries of the world, it is almost nonexistent in many
African nations and underdeveloped countries. This
suggests that factors such as lack of fiber in the diet,
a decrease in physical activity, and poor bowel habits
(e.g., neglecting the urge to defecate), along with the
effects of aging, contribute to the development of the
disease.
True diverticula involve all layers of the intestinal
wall. The abnormal structures in diverticulosis are
instead pseudodiverticula, in which only the mucosa
and submucosa are herniated through the muscle lay-
ers.
6,7
The diverticula are often multiple, ranging from
a solitary herniation to several hundred (Fig. 29-8).
They are most often located in the sigmoid colon, but
more extensive areas may be involved in severe cases.
Microscopically, colonic diverticula are small, flasklike
outpouchings, usually 0.5 to 1.0 cm in diameter, that
occur in a regular distribution alongside the teniae coli
(Fig. 29-9).
Colonic diverticula result from the unique structure
and elevated luminal pressures in the sigmoid colon.
6
In the colon, the longitudinal muscle does not form a
continuous layer, as it does in the small bowel. Instead,
there are three separate longitudinal bands of muscle
called the
teniae coli.
In a manner similar to the small
intestine, bands of circular muscle constrict the large
intestine. As the circular muscle contracts at each of
these points (approximately every 2.5 cm), the lumen
of the bowel becomes constricted, so that it is almost
occluded. The combined contraction of the circular
muscle and the lack of a continuous longitudinal muscle
