1. Diarrhea is traditionally defined as increase in frequency of stool or decrease in consistency, based upon the individual’s baseline.

2. Other definitions include three or more loose or watery stools per day and stool weight > 200 g/day.

1. Acute diarrhea consists of diarrhea lasting ≤14 days.

2. Chronic diarrhea is defined as diarrhea continuing for >30 days. Diarrhea lasting >14 days but <30 days is sometimes termed persistent diarrhea.

1. Food- and water-borne gastroenteritis accounts for most cases of acute diarrhea, approximately 89 million cases per year. Risk factors include sick contacts, pregnancy, travel, well water, pets, immunosuppression, HIV, homosexual males, and day care exposure. Non-food-or waterborne illness accounts for 122 million cases per year.

2. The prevalence of chronic diarrhea in the United States is estimated to be 5%.

3. Diarrhea is a frequent complication in critically ill patients occurring in 40% to 50% of patients in the intensive care unit (ICU). If untreated, it can produce serious fluid and electrolyte imbalance, skin breakdown, local infection, and difficulty with nutritional management.

4. Diarrhea is listed as a cause of death in over 3,000 people per year in the United States. The mortality in the elderly (>60 years) can be as high as 85%.

1. Typical etiologies in the community may also apply to the patient in intensive care. The most commonly reported cause of acute gastroenteritis in the community is norovirus (Norwalk); other viral etiologies include rotavirus, enteric adenovirus types 40 and 41, and astrovirus. Salmonella and Campylobacter are common bacterial causes. Bloody diarrhea can typically result from Shigella and Escherichia coli O157:H7 infections. Amebiasis can also cause bloody diarrhea and dysentery.
Fungal and mycobacterial diarrhea are rare. Brainerd diarrhea is a chronic or persistent cause of diarrhea of rather acute onset but unclear etiology, first reported in Brainerd, Minnesota.

2. Clostridium difficile toxin-induced colitis is implicated in 15% to 20% of cases. Clindamycin, penicillin, and broad-spectrum cephalosporins are commonly associated with the diagnosis.

3. In the immunosuppressed and the elderly, cytomegalovirus (CMV) or herpes simplex virus (HSV) may be implicated.

1. Medications.

a. Antibiotics, especially erythromycin, ampicillin, clindamycin, cephalosporins, and azithromycin, cause iatrogenic diarrhea in 3% to 29% of patients. Alterations in intestinal flora, breakdown of dietary carbohydrate products, and prokinetic effects (e.g., from erythromycin) are all postulated mechanisms for antibiotic-related diarrhea.

b. Other medications implicated in the development of diarrhea include antacids (magnesium containing), magnesium and phosphorus supplements, lactulose, colchicine, digitalis, quinidine, theophylline, levothyroxine, aspirin, nonsteroidal anti-inflammatory agents, cimetidine, misoprostol, diuretics, β-blocking agents, chemotherapeutic agents, proton-pump inhibitors, and antiretroviral medications such as nelfinavir. These medications rarely cause severe diarrhea.

2. Enteral feeding.

a. Diarrhea frequently occurs in enterally fed patients and is usually associated with concurrent antibiotic use.

b. Osmolarity of the enteral solution can play a role in some instances, as can bolus feeding distal to the pylorus.

c. Enteral formulas high in lactose or fat content may precipitate diarrhea in susceptible patients.

1. Inflammatory bowel disease (IBD): The two named IBDs are Crohn’s disease, which can affect any part of the luminal gut; and ulcerative colitis, which only affects the colon within the luminal gut. Less common patterns of inflammatory mucosal disease include lymphocytic colitis, collagenous colitis, autoimmune enteritis, celiac disease, sarcoid, graft-versus-host disease (GVHD), and other idiopathic processes. Fulminant colitis is addressed elsewhere (see Chapter 76).

2. Malignancy: Certain types of adenocarcinoma can cause diarrhea, especially those with villous patterns. Lymphoma, carcinoid, gastrinoma, VIPoma, and somatostatinoma can also present as diarrhea.

3. Anatomical causes: Short gut syndrome, where <200 cm of functional small intestine remains, can manifest with prominent diarrhea that can be particularly worsened by severe intercurrent illness. Subtotal gastrectomy, roux-en-Y gastric bypass, ileocolonic resection, and subtotal colectomy may also be associated with diarrhea.

4. Other causes: This includes sepsis, vasculitis, diabetic diarrhea, renal failure, pancreatic exocrine insufficiency, and adrenal insufficiency.

1. Infections, neoplastic disease in immunosuppressed patients, and neutropenic enteropathy.

2. Gastrointestinal (GI) bleeding and ischemic bowel can be associated with diarrhea. Chronic mesenteric ischemia can also manifest as diarrhea.

3. Other causes include fecal impaction and opiate withdrawal.

1. History.

a. Attention to historical data (e.g., onset, duration, character, relation to antibiotic usage, or enteral feeding) may lead to prompt diagnosis and management.

b. Clostridium difficile-related diarrhea may occur up to 8 weeks after the offending antibiotic is discontinued.

c. Abdominal pain suggests ischemia, infection, or inflammatory conditions, such as vasculitis or GVHD, depending on the clinical setting.

d. Bloody diarrhea may indicate overt GI bleeding, ischemic colitis, or occasionally pseudomembranous colitis.

e. Passage of frequent small-volume stools with urgency or tenesmus suggests distal colonic involvement, whereas passage of less-frequent, large-volume stools suggests a more proximal process.

f. Medication lists and tube feeding formulae should be scrutinized.

2.

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