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What is Diarrhea?

Diarrhea—loose, watery stools occurring more than three times in one day
is a common problem that usually lasts a day or two and goes away on its own without any special treatment.
However, prolonged diarrhea can be a sign of other problems.
Diarrhea can cause dehydration, which means the body lacks enough fluid to function properly.
Dehydration is particularly dangerous in children and the elderly, and it must be treated promptly to avoid serious health problems.
Dehydration is discussed below.
People of all ages can get diarrhea.
The average adult has a bout of diarrhea about four times a year.

It is not a disease/disorder on its own. It is a symptom, as a result of another condition or problem.
Diarrhea causes loss of body minerals including sodium, potassium, magnesium and chloride.
In most acute cases, the illness is brief and at most an inconvenience and for the otherwise healthy adult it can be easily managed.

Watery diarrhea caused by viruses usually lasts less than 3 days.
Diarrhea lasting more than 2 weeks is chronic diarrhea.
Blood or mucus in the stool may mean inflammatory bowel disease or bacterial infection.
Loose bowel movements with bloating or flatus are often caused by lactose (in nonfermented dairy products) or complex carbohydrates (often found in beans).
Sorbitol in sugarless chewing gum causes diarrhea in people who can't absorb it.
Half of patients referred to specialists for evaluation of diarrhea have no disease.
These patients are usually women under 50 yrs old. They have had the problem for a long time.
Symptoms are worsened by stress.
Abdominal pain is relieved by defecation.
Persons with diseases causing diarrhea usually have blood or mucus in the stool, have diarrhea during the night, have a sudden onset of symptoms, and/or have lost more than 5 lbs.

some common causes and their characteristics.

Viral (stomach flu) gastroenteritis
Nausea, vomiting, watery diarrhea, fever, aches. Usually 1-3 days.
Bacterial infection
Diarrhea, fever, chills, sometimes blood or mucus in the stools. Vomiting less common.
Food intolerance/lactose intolerance
Bloating, gas, cramps, loose stools hours after eating dairy products or other offending foods. No other signs of illness or infection.
Emotional distress
Cramping, loose stools, predictable during times of stress.

Most types of diarrhea in the U.S. are harmless and will go away by themselves within hours to days. As long as you don’t get dehydrated, there’s little to worry about. There are two exceptions, though; bacterial infection and giardiasis.
Bacterial infection. Salmonella, campylobacter, e. choli and shigella are the most common types of bacterial infection causing diarrhea in this country. There serious conditions need immediate physician evaluation for proper treatment. See the chart above for classic signs of bacterial diarrhea.

Giardiasis. This parasite usually infects young children, usually in day care settings where it is passed child to child by direct contact, and by adults changing different children’s diapers without hand washing in between. Family members of affected children are also at risk. Giardiasis can last months or longer without treatment, and spread rapidly. Finding the source and testing or treating all contacts is important, since some people carry and spread the infection without having diarrhea themselves.
By now you realize how varied the types and causes of diarrhea are. Don’t get too confused or worried through --- since the vast majority of diarrhea episodes are the harmless types, the odds are with you. Just watch for signs of the more serious type infections

 Parasitic Causes

Giardia lamblia
Entamoeba histolytica

 Viral Causes

Norwalk Agent

Bacterial infections. Several types of bacteria, consumed through contaminated food or water, can cause diarrhea. Common culprits include Campylobacter, Salmonella, Shigella, and Escherichia coli.
Viral infections. Many viruses cause diarrhea, including rotavirus, Norwalk virus, cytomegalovirus, herpes simplex virus, and viral hepatitis.
Food intolerances. Some people are unable to digest a component of food, such as lactose, the sugar found in milk.
Parasites. Parasites can enter the body through food or water and settle in the digestive system. Parasites that cause diarrhea include Giardia lamblia, Entamoeba histolytica, and Cryptosporidium.
Reaction to medicines, such as antibiotics, blood pressure medications, and antacids containing magnesium.
Intestinal diseases, like inflammatory bowel disease or celiac disease.
Functional bowel disorders, such as irritable bowel syndrome, in which the intestines do not work normally.
Some people develop diarrhea after stomach surgery or removal of the gallbladder. The reason may be a change in how quickly food moves through the digestive system after stomach surgery or an increase in bile in the colon that can occur after gallbladder surgery.
In many cases, the cause of diarrhea cannot be found. As long as diarrhea goes away on its own, an extensive search for the cause is not usually necessary.
People who visit foreign countries are at risk for traveler's diarrhea, which is caused by eating food or drinking water contaminated with bacteria, viruses, or, sometimes, parasites. Traveler's diarrhea is a particular problem for people visiting developing countries. Visitors to the United States, Canada, most European countries, Japan, Australia, and New Zealand do not face much risk for traveler's diarrhea.

Traveler's Diarrhea
Even the healthiest and best prepared traveler may succumb to the disruption of routine caused by changes in time zones, unusual foods, increased physical exercise, extreme variations in altitude, and exposure to unfamiliar viruses and bacteria.
Traveler's diarrhea is not a single entity or disease. It is a group of illnesses linked by the common symptom of loose or watery stools.
Traveler's diarrhea is caused by various bacteria, viruses or parasites which are indigenous to the area and have contaminated the food or water.
Local residents usually are protected by immunity from previous exposure, but because of the variety of microorganisms which can trigger symptoms, one attack of diarrhea does not provide immunity for most travelers.
Studies have shown that persons traveling from more developed to less developed areas are at greater risk.
Those who eat in private homes are less likely to develop symptoms than persons eating most of their meals in restaurants.
Food from street vendors is most likely to precipitate diarrhea.
 Acute Diarrhea
The usual condition associated with traveler's diarrhea.
This typically affects newcomers from cooler climates within 14 days (often between days 2 to 5) of arrival in warmer or tropical areas.
Onset of symptoms is abrupt, with abdominal cramps and nausea followed by loose, then watery stools.
Other common symptoms include:
low-grade fever (under 101 degrees F)
occasional vomiting
The illness is most severe on the first day and subsides over the next several days without therapy.
Complete recovery occurs in most people within three to seven days.

Distinguished from the above by the presence of:
blood and/or mucus in the stool
more severe cramping
usually a fever above 101 degrees F
These symptoms require examination by a physician.

 Chronic Diarrhea
During or after a trip is often a change to loose but not watery stools (commonly alternating with constipation) and may last weeks to months.
This is often due to a parasitic infection, usually Giardia, and may be diagnosed and treated upon return.

Diarrhea In Infants

Most common cause is gastroenteritis

Diarrhea In Adults
Diarrhea may be accompanied by cramping abdominal pain, bloating, nausea, or an urgent need to use the bathroom. Depending on the cause, a person may have a fever or bloody stools.
Diarrhea can be either acute or chronic. The acute form, which lasts less than 3 weeks, is usually related to a bacterial, viral, or parasitic infection. Chronic diarrhea lasts more than 3 weeks and is usually related to functional disorders like irritable bowel syndrome or diseases like celiac disease or inflammatory bowel disease.


Diarrhea in Children
Children can have acute (short-term) or chronic (long-term) forms of diarrhea. Causes include bacteria, viruses, parasites, medications, functional disorders, and food sensitivities. Infection with the rotavirus is the most common cause of acute childhood diarrhea. Rotavirus diarrhea usually resolves in 5 to 8 days. A vaccine to prevent rotavirus infection is now available for infants under 6 months of age.
Medications to treat diarrhea in adults can be dangerous to children and should be given only under a doctor's guidance.
Diarrhea can be dangerous in newborns and infants. In small children, severe diarrhea lasting just a day or two can lead to dehydration. Because a child can die from dehydration within a few days, the main treatment for diarrhea in children is rehydration. Rehydration is discussed below.
Take your child to the doctor if any of the following symptoms appear:
Stools containing blood or pus, or black stools.
Temperature above 101.4 degrees Fahrenheit.
No improvement after 24 hours.
Signs of dehydration

Causes of Acute Diarrhea
Food poisoining
If diarrhea starts within 6 hours of eating (contamination with Staphyloccocus or Clostridium bacteria)
If it develops 12-48 hours after eating (due to contamination by Salmonella or Campylobacter bacteria or by viruses such as Rotavirus or Norwalk virus)
Other Causes
Shigellosis (an infection caused by bacteria Shigella; presents with blood in stool)
Typhoid and Parathyphoid
Drug toxicity
food allergy
food intolerance

Causes of Chronic Diarrhea (repeats itself)
With blood in stool
Cancer of the large intestine
Crohn's Disease
Diverticular Disease
Ulcerative Colitis
Without blood in stool
Irritable Bowel Syndrome (IBS)

Acute diarrhea is defined as diarrheal disease of rapid onset, often with nausea, vomiting, fever, or abdominal pain. Most episodes of acute gastroenteritis will resolve within 3 to 7 days.
Clinical Evaluation of Acute Diarrhea
The nature of onset, duration, frequency, and timing of the diarrheal episodes should be assessed. The appearance of the stool, buoyancy, presence of blood or mucus, vomiting, or pain should be determined.
Contact with a potential source of infectious diarrhea has occurred.
Drugs that may cause diarrhea include laxatives, magnesium-containing compounds, sulfa-drugs, antibiotics.
Physical Examination
Assessment of Volume Status. Dehydration is suggested by dry mucous membranes, orthostatic hypotension, tachycardia, mental status changes, and acute weight loss.
Abdominal tenderness, mild distention and hyperactive bowel sounds are common in acute infectious diarrhea. However, the presence of peritoneal signs or rigidity suggests toxic megacolon or perforation, requiring radiologic examination of the abdomen.
Evidence of systemic atherosclerosis suggests ischemia. Lower extremity edema suggests malabsorption or protein loss.
Acute Infectious Diarrhea
Infectious diarrhea is usually classified as noninflammatory or inflammatory, depending on whether the infectious organism has invaded the intestinal mucosa.
Noninflammatory infectious diarrhea is caused by organisms that produce a toxin (enterotoxigenic E coli strains, Vibrio cholerae). Noninflammatory, infectious diarrhea is usually self-limiting and lasts less than 3 days.
Blood or mucus in the stool suggests inflammatory disease, usually caused by bacterial invasion of the mucosa (enteroinvasive E coli, Shigella, Salmonella, Campylobacter). Patients usually have a septic appearance and fever; some have abdominal rigidity and severe abdominal pain.
Vomiting out of proportion to diarrhea is usually related to a neuroenterotoxin-mediated food poisoning from Staphylococcus aureus or Bacillus cereus, or from an enteric virus, such as rotavirus (in an infant), or a small round virus, such as Norwalk virus (in older children or adults). The incubation period for neuroenterotoxin food poisoning is less than 4 hours, while that of a viral agent is more than 8 hours.
Traveler's diarrhea is a common type of acute infectious diarrhea. Typically, three or four unformed stools are passed per 24 hours, usually starting on the third day of travel and lasting 2-3 days. Accompanying symptoms may include anorexia, nausea, vomiting, abdominal cramps, abdominal bloating, and flatulence.
Antibiotic-Related Diarrhea
Diarrhea ranges from mild illness to life-threatening pseudomembranous colitis. Overgrowth of Clostridium difficile causes pseudomembranous colitis. Amoxicillin, cephalosporins and clindamycin have been implicated most often, but almost any antibiotic can be the cause.
Patients with pseudomembranous colitis have high fever, cramping, leukocytosis, and severe, watery diarrhea.
Latex agglutination testing for C difficile toxin can provide results in 30 minutes.
Enterotoxigenic E Coli
The enterotoxigenic E coli include the E coli serotype 0157:H7. Grossly bloody diarrhea is most often caused by E. coli 0157:H7, causing 8% of grossly bloody stools.
Enterotoxigenic E coli can cause hemolytic uremic syndrome, thrombotic thrombocytopenic purpura, intestinal perforation, sepsis, and rectal prolapse.
Diagnostic Approach to Acute Infectious Diarrhea
An attempt should be made to obtain a pathologic diagnosis in patients who give a history of recent ingestion of seafood ( Vibrio parahaemolyticus), travel or camping, antibiotic use, homosexual activity, or who complain of fever and abdominal pain.
Blood or mucus in the stools indicates the presence of Shigella, Salmonella, Campylobacter jejuni, enteroinvasive E. coli, C. difficile, or, less likely, Yersinia enterocolitica.
Most cases of mild diarrheal disease do not require laboratory studies to determine the etiology. In moderate to severe diarrhea with fever or pus in stools, a liquid stool culture for bacterial pathogens (Salmonella, Shigella, Campylobacter) is submitted. If antibiotics were used recently, stool should be sent for Clostridium difficile toxin.
Laboratory Tests and Procedures for Acute Diarrhea
Fecal leukocytes is a screening test which should be obtained if moderate to severe diarrhea is present. Numerous leukocytes indicate Shigella, Salmonella, or Campylobacter jejuni.
Stool cultures for bacterial pathogens should be obtained if high fevers, severe or persistent (>14 d) diarrhea, bloody stools, or leukocytes are present.
Examination for ova and parasites is indicated for persistent diarrhea (>14 d), travel to a high-risk region, gay males, infants in day care, or dysentery.
Blood cultures should be obtained prior to starting antibiotics if severe diarrhea and high fever is present.
E coli 0157:H7 Cultures. Enterotoxigenic E coli should be suspected if there are bloody stools with minimal fever, or when diarrhea follows hamburger or fast food consumption, or when hemolytic uremic syndrome is diagnosed.
Clostridium difficile cytotoxin should be obtained if diarrhea follows use of an antimicrobial agent.
Rotavirus antigen test (Rotazyme) is indicated for hospitalized children <2 years old with gastroenteritis. The finding of rotavirus eliminates the need for antibiotics.
Treatment of Acute Diarrhea
Fluid and Electrolyte Resuscitation
Oral Rehydration. For cases of mild to moderate diarrhea in children, Pedialyte or Ricelyte should be administered. For adults with travelers' diarrhea, flavored soft drinks with saltine crackers is usually adequate.
Intravenous hydration should be used if oral rehydration is not possible; potassium may be added.
Fatty foods and foods high in simple sugars, such as sweetened tea, juices, and soft drinks should be avoided.
Well-tolerated foods include complex carbohydrates (rice, wheat, potatoes, bread, and cereals), lean meats, yogurt, fruits, and vegetables.
Diarrhea often is associated with a reduction in intestinal lactase. A lactose-free milk preparation may be substituted, if lactose intolerance becomes apparent.
Antimicrobial Treatment of Acute Diarrhea
Empiric Drug Therapy
Febrile Dysenteric Syndrome
If diarrhea is associated with high fever and stools containing mucus and blood, empiric antibacterial therapy should be given for Shigella or Campylobacter jejuni.
Adults: Norfloxacin ( Noroxin) 400 mg bid, ciprofloxacin ( Cipro) 500 mg bid, ofloxacin ( Floxin) 300 mg bid for 3-5 days.
Children: Ceftriaxone or cefixime (Suprax).
Travelers' Diarrhea. Acute Travelers’ Diarrhea. Children with severe cases are treated with TMP/SMX and erythromycin. Adults are treated with norfloxacin 400 mg bid, ciprofloxacin 500 mg bid, or ofloxacin 300 mg bid for 3 days.
§Diarrhea is considered chronic if it occurs acutely, subsides, and then returns, or if it lasts longer than 2 weeks.
Clinical evaluation of chronic diarrhea
Initial evaluation should determine the characteristics of the diarrhea, including volume, mucus, blood, flatus, cramps, tenesmus, duration, frequency, effect of fasting, stress, and the effect of specific foods (eg, dairy products, wheat, laxatives, fruits).
Secretory diarrhea
Secretory diarrhea is characterized by large stool volumes (>1 L/day), no decrease with fasting, and a fecal osmotic gap <40.
Evaluation of secretory diarrhea consists of a giardia antigen, Entamoeba histolytica antibody, Yersinia culture, fasting serum glucose, thyroid function tests, and a cholestyramine (Cholybar, Questran) trial.
Osmotic diarrhea
Osmotic diarrhea is characterized by small stool volumes, a decrease with fasting, and a fecal osmotic gap >40. Postprandial diarrhea with bloating or flatus also suggests osmotic diarrhea. Ingestion of an osmotically active laxative may be inadvertent (sugarless gum containing sorbitol) or covert (with eating disorders).
Evaluation of osmotic diarrhea
Trial of lactose withdrawal.
Trial of an antibiotic (metronidazole) for small-bowel bacterial overgrowth.
Screening for celiac disease (anti-endomysial antibody, antigliadin antibody).
Fecal fat measurement (72 hr) for pancreatic insufficiency.
Trial of fructose avoidance.
Stool test for phenolphthalein and magnesium if laxative abuse is suspected.
Hydrogen breath analysis to identify disaccharidase deficiency or bacterial overgrowth.
Exudative diarrhea
Exudative diarrhea is characterized by bloody stools, tenesmus, urgency, cramping pain, and nocturnal occurrence. It is most often caused by inflammatory bowel disease, which may be indicated by the presence of anemia, hypoalbuminemia, and an increased sedimentation rate.
Evaluation of exudative diarrhea consists of a complete blood cell count, serum albumin, total protein, erythrocyte sedimentation rate, electrolyte measurement, Entamoeba histolytica antibody titers, stool culture, Clostridium difficile antigen test, ova and parasite testing, and flexible sigmoidoscopy and biopsies.
Diarrhea in HIV-Infected Patients
Michael A. Davis, MD
Gastrointestinal disease is a major problem in patients with HIV and AIDS, and diarrhea is reported in up to 60% of patients with AIDS. Diarrhea may wax and wane over time, and in at least 30% of patients, an etiology cannot be determined. In such cases, the diarrhea is often attributed to HIV enteropathy.
I. Clinical Evaluation of AIDS-Associated Diarrhea
A. The history should include the duration of symptoms, frequency and characteristics of stools, and the CD4 count. The amount and rate of weight loss, residential exposures, occupational exposures, recent travel, pets, hobbies (ie, fishing, hunting, cooking), and type of water supply should be assessed.
B. Recent antibiotic or antiretroviral use, previous opportunistic infections, and other illnesses or hospitalizations should be assessed.
C. Sexually transmitted diseases, intake of unpasteurized dairy products, or raw or under-cooked meat or shellfish should be sought.
D.  Small-bowel diarrhea is generally watery and occurs in large volume (up to 10,000 mL/day).
1. Abdominal cramping, bloating, gas, and profound weight loss may occur.
2. Fever is absent and stool examinations for occult blood and fecal leukocytes are negative.
E. Large-bowel Disease is characterized by frequent, regular, small-volume, often painful bowel movements. Fever and bloody or mucoid stools are common, and fecal leukocytes are positive.
F. Systemic Diseases, such as disseminated  Mycobacterium avium infection, may present with diarrhea with persistent fever, severe weight loss, and symptomatic anemia.
CD4 Count as a Predictor of Pathogens Causing Diarrheal Disease
CD4+ Count
Shigella Campylobacter  
Clostridium difficile  
Mycobacterium tuberculosis
Escherichia coli  
Mycobacterium avium
Herpes simplex virus  
Giardia lamblia  
Entamoeba histolytica
II. Physical Examination
A. Height and weight, temperature, orthostatic blood pressure, and degree of wasting are documented.
B. Dermatitis may suggest zinc deficiency and stomatitis may suggest vitamin B-12 deficiency.
C. CMV retinitis raises the possibility that gastrointestinal disease may also be caused by CMV.  
D. Organomegaly may be the first sign of disseminated mycobacterial infection, histoplasmosis, or lymphoma.
E. Neurologic examination should include an assessment of long tract function (vibration and position sense) which may indicate vitamin B-12 deficiency.
III. Laboratory Evaluation of Diarrhea
A. Initial evaluation consists of stool cultures for enteric organisms, an assay for C. difficile toxin (not culture), fecal leukocyte count, and examination for ova and parasites.
B. Blood cultures for bacteria are appropriate in febrile patients.
C. In febrile patients with a CD4 cell count <200, two sets of blood cultures for mycobacteria or fungi should also be submitted.
D. Modified acid-fast smear for cryptosporidia is appropriate in patients with very low CD4 cell counts and severe diarrhea.
E. If the initial evaluation is negative, the studies should be repeated once or twice more in case a pathogen was missed. If these tests are negative and diarrhea persists, options include flexible sigmoidoscopy or colonoscopy and treating empirically with antidiarrheals.
IV. Symptomatic Treatment of Chronic Diarrhea
A. Loperamide ( Imodium) 4 mg po initially, then 2 mg q6h around the clock and prn (maximum 16 mg qd).
B. Diphenoxylate-atropine ( Lomotil) 2.5-5 mg po 3-6 times daily for 24-48 hr, then 2.5-5 mg tid and prn to control diarrhea (maximum 20 mg qd).
C.  Paregoric 0.4 mg morphine/mL, 5-10 mL qd-qid.
V. Bacterial Small-bowel Pathogens
A. Salmonella
1. Salmonella can involve either the small or large bowel or both. It often causes watery, non-bloody, non-mucoid diarrhea typical of small-bowel disease. Fever is often present.
2. Salmonella infection can develop before and after the diagnosis of AIDS.
3. Blood cultures should be submitted when this diagnosis is suspected.
4. Relapses are common without maintenance therapy. Antibiotics active against Salmonella (ie, trimethoprim-sulfamethoxazole, fluoroquinolone) prevent relapse.
B. Mycobacteria
1. Mycobacterium avium complex and Mycobacterium tuberculosis both cause systemic infections in AIDS, although M. avium is much more commonly associated with diarrheal disease. MAC affects 25% of AIDS patients.
2. Disseminated M. avium infection generally occurs several months after the diagnosis of AIDS. CD4 counts are in the range of 60 cells/µL, and infection in those with counts >100 cells/µL is rare.
3. Malabsorptive diarrhea, persistent fever and weight loss are typical of small bowel involvement.
4. Focal lesions of the gastrointestinal tract often involve the duodenum, and organisms characteristically disseminate to bone-marrow, liver,spleen and lymph nodes.
5. Blood cultures are 98% sensitive if two samples are submitted. Neither a positive stool culture for MAC nor the presence of acid-fast organisms on smear is diagnostic; however, the smear is strongly suggestive of intestinal infection.
VI.  Protozoa Small Bowel Pathogens
A.  Cryptosporidium enteritis most often occurs in patients with AIDS, and it is the most common cause of diarrhea in this group (16%).
1. Small-bowel disease is characterized by large-volume non-bloody diarrhea, nausea, vomiting, abdominal pain, and weight loss. Gastric outlet obstruction, colitis and toxic megacolon may occur.
2. Cryptosporidia is one of the more common causes of chronic, seemingly pathogen-negative diarrhea.
3. CD4 counts >180 cells/µL are associated with spontaneous resolution of diarrhea within 1-4 weeks. However, counts <180 cells/µL are associated with persistent disease.
4. Modified Ziehl-Neelsen or immunofluorescence staining of a stool sample generally reveals the pathogen.
B.  Microsporidia
1. This disorder is characterized by chronic, intermittent, watery, non-bloody diarrhea and weight loss without fever or abdominal pain.
2. Patients usually have CD4 values of <30-35 cells/µL. Therefore, the initial evaluation of diarrhea in HIV-infected patients with CD4 counts above 100 cells/µL need not include tests for Microsporidia.
3. Modified trichrome and chitin stains are diagnostic.
C.  Isospora belli
1. Isospora belli causes a chronic diarrheal syndrome indistinguishable from that caused by Cryptosporidia.
2. Infection with this pathogen is rare in the United States, and those affected are primarily immigrants from Mexico, Latin and Central America.
3. Eosinophilia and an appropriate exposure history in an AIDS patient with diarrhea suggests I. belli.
VII. HIV Small Bowel Enteropathy
A. HIV itself may cause a "pathogen-free" chronic diarrhea in AIDS patients.
B. Some HIV-infected patients with relatively intact immune systems develop chronic diarrhea in the absence of identifiable pathogens.
C. A search for other pathogens should be completed before attributing diarrheal disease to  HIV enteropathy.
VIII. Bacterial Large-bowel Pathogens
A.  Shigella
1. Shigella causes bacillary dysentery, and it presents with abdominal cramping, tenesmus and frequent small-volume bloody stools.
2. Fever is present in 50%, and bacteremia is more frequent in HIV-infected patients.
3. HIV-infected patients are not particularly predisposed to infection with Shigella.
B.  Campylobacter
1. Campylobacter occasionally involves the small bowel, but usually causes proctocolitis, with cramping and bloody diarrhea. It often causes prolonged diarrhea in HIV-infected patients.
2. Campylobacter enteritis may present with negative stool cultures, and biopsy for cultures may be necessary.
C.  Clostridium difficile. This bacterium causes antibiotic-associateddiarrhea and life-threatening pseudomembranous colitis.
D.  Vibrio parahaemolyticus is an important cause of acute colitis related to the ingestion of inadequately cooked or raw seafood.
E. Enterohemorrhagic or  Verocytotoxin-Producing E. coli. These agents are responsible for hemorrhagic colitis, hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP). Outbreaks and sporadic cases have been reported.
IX. Viral Large Bowel Pathogens
A.  Cytomegalovirus
1. CMV, a herpes virus, is ubiquitous in patients with AIDS. It most commonly manifests as retinitis. However, it can also cause encephalitis, pneumonia, hepatitis, adrenalitis, sinusitis, and gastrointestinal disease.
2. Risk for developing CMV disease increases when the CD4 count falls below 100 cells/µL.
3. CMV can occur anywhere from the mouth to the anus and can cause panenterocolitis in patients with AIDS. Colitis is the most common type of GI involvement.
4. Symptoms of CMV colitis include chronic diarrhea, crampy abdominal pain, weight loss, hematochezia and fever.
5. Only 30% of patients with CMV colitis have positive blood cultures. The diagnosis is made by biopsy.