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Clinical approach

Last updated on May 12, 2023

It is helpful to classify diarrhea into clinical categories, taking into consideration the duration, setting, and sexual preference of the patient. Diarrhea of abrupt onset of less than 2 to 3 weeks’ duration is called acute diarrhea. If the diarrheal illness lasts longer than 3 weeks, it is called chronic diarrhea. If diarrhea occurs in the setting of antibiotic therapy or after a course of antibiotics, antibiotic-associated diarrhea and pseudomembranous colitis due to C. difficile cytotoxin should be considered.

Acute diarrhea. The most common cause of acute diarrhea is infection

Food poisoning is produced by a preformed bacterial toxin that contaminates the food. Bacterial replication in the host is not necessary for the development of disease. The resultant illness usually has an acute onset and short duration and occurs in small, well-defined epidemics, without evidence of secondary spread.

Diarrhea resulting from multiplication of organisms in the intestine may be divided into inflammatory-invasive versus noninflammatory-noninvasive categories. Most of these types of diarrhea result from ingestion of contaminated food or water after 1 to 2 days of incubation. Animal reservoirs may exist for some common pathogens, including Salmonella, Campylobacter, Yersinia, Giardia, Cryptosporidium, and Vibrio parahaemolyticus. Waterborne disease in which the pathogens are spread from animals or water to humans is caused by Salmonella, Campylobacter, Shigella, Norwalk virus, Giardia, Vibrio cholerae, toxigenic Escherichia coli, and E. coli: H7.

Diarrhea developing in individuals during or just after traveling is commonly infectious. The most likely organisms are enterotoxigenic E. coli, Salmonella, Giardia, and amebae.

Causes Characteristics Organisms
Viral Infections
Small intestine Mucosal invasion absent Rotavirus (children, adults)
Noninflammatory Norwalk virus
Watery diarrhea
Fecal leukocyte absent
Enteric adenovirus
Bacterial infections
Small intestine Mucosal invasion absent Vibrio cholerae
Noninflammatory Toxigenic Escherichia coli
Watery diarrhea
Fecal leukocytes absent
Colon Mucosal invasion present Salmonella
Inflammatory Shigella
Bloody diarrhea Campylobacter
Fecal leukocytes present Yersinia enterocolitica
Invasive E. coli
E. coli 0157:H7
Staphylococcus aureus (toxin)
Vibrio parahaemolyticus (toxin)
Clostridium difficile (toxin)
Parasitic infections
Small intestine Mucosal invasion absent Giardia lamblia
Watery diarrhea
Fecal leukocytes absent
Colon Mucosal invasion present Entamoeba histolytica
Bloody diarrhea
Fecal leukocytes present
Food poisoning
Small intestine Toxin induced Staphylococcus aureus
Mucosal invasion absent Bacillus cereus
Noninflammatory Clostridium perfringens
Watery diarrhea Clostridium botulinum
Antacids (Mg2+, Ca2+ salts)
Nonsteroidal antiinflammatory drugs
Chemotherapeutic agents
Heavy metals (Hg, Pb)
Cholinergic agents
Fecal impaction
Ischemic bowel disease
Type Agent
Infection Giardia lamblia
Entamoeba histolytica
Tubercle bacillus
Clostridium difficile
Inflammation Ulcerative colitis
Microscopic colitis
Collagenous colitis
Crohn’s disease
Ischemic colitis/enteritis
Solitary rectal ulcer
Drugs Laxatives
Nonsteroidal antiinflammatory drugs
Malabsorption Small-bowel mucosal disease
Disaccharidase deficiency
Pancreatic insufficiency
Ischemic/radiation enteritis
Short-bowel syndrome
Bacterial overgrowth
Endocrine Zollinger-Ellison syndrome
Non-ОІ-cell pancreatic tumor
Villous adenoma
Motility disorders Irritable bowel syndrome
Postvagotomy syndrome
Postgastric surgery dumping syndrome
Tumor/fecal impaction overflow diarrhea
Narcotic bowel

Homosexual individuals are at a higher risk of exposure to infectious agents. In this setting, it is important to consider amebiasis, giardiasis, shigellosis, rectal syphilis, rectal gonorrhea, and lymphogranuloma venereum caused by Chlamydia trachomatis, and herpes simplex infections of the rectum and perianal area. In patients with acquired immunodeficiency syndrome (acquired immunodeficiency syndrome), infectious agents could include cytomegalovirus, Cryptosporidium, and Candida as well as all of the organisms noted in homosexual persons and immunocompetent individuals.

Chronic and recurrent diarrhea

Any diarrheal illness lasting longer than 3 weeks should be clinically investigated.


Most viral and bacterial diarrheas are self-limiting and abate within 3 weeks. Diarrhea from Campylobacter and Yersinia may last a few months but rarely becomes chronic. Bowel infections with tuberculosis, amebae, and Giardia may become chronic.

Inflammatory bowel disease

Ulcerative colitis and Crohn’s disease may result in diarrhea of varying severity, depending on the extent and degree of bowel involvement. Diarrhea in Crohn’s disease of the small bowel may be compounded by concomitant bile salt and fat malabsorption.

Malabsorption syndromes

Diseases of the small intestine may cause chronic diarrhea of varying severity. The mechanism of the diarrhea is usually multifactorial and complex. These diseases include:

  • Sprue (nontropical, tropical).
  • Amyloidosis.
  • Whipple’s disease.
  • Lymphoma.
  • Carcinoid.
  • Radiation enteritis.
  • Lymphangiectasia.
  • Bowel resection/bypass.
  • Pancreatic insufficiency from chronic pancreatitis and cystic fibrosis may cause severe fat malabsorption, resulting in chronic diarrhea.

Zollinger-Ellison syndrome resulting from a gastrin-secreting tumor causes increased gastric acid output that overwhelms the absorptive capacity of the proximal small intestine, neutralizes the bicarbonate, and inactivates the pancreatic enzymes secreted into the duodenum. The resulting diarrhea is complicated by malabsorption and bile salt – and fatty acid – stimulated colonic secretion.

Postgastrectomy, enterostomy states may result in diarrhea due to decreased mucosal-chyme exposure as well as poor mixing of digestive juices with luminal contents, resulting in malabsorption.

Bacterial overgrowth of the small intestine may occur in patients with diabetes mellitus, scleroderma, amyloidosis, blind loop syndrome, and large and multiple diverticula of the small bowel. Bacterial degradation of carbohydrates, fatty acids, and bile salts results in diarrhea.

Disaccharidase deficiency

Lactase is deficient to a variable degree in many adult populations, especially in blacks, Asians, southern Europeans, and those of Jewish descent. Even small amounts of dairy products may cause intermittent diarrhea in these individuals.

Endocrine disorders

  • Hyperthyroidism.
  • Diabetes mellitus.
  • Adrenal insufficiency.
  • Carcinoid.
  • Medullary thyroid cancer.
  • Hormone-secreting pancreatic tumors.
  • Tumors secreting vasoactive intestinal polypeptide.
  • Gastrinoma.
  • Neoplasms. Villous adenoma, colon cancer with obstruction, and fecal impaction may present with diarrhea.

Drugs and laxatives

Surreptitious use of laxatives and drugs should always be considered in the evaluation of chronic diarrhea.

Irritable bowel syndrome is very common and may present with only chronic intermittent diarrhea, constipation, or a combination of both. Most patients also complain of abdominal cramps, gas, belching, and mucous stools.

Incontinence of stool

Anal sphincter dysfunction due to the presence of fissures, fistulas, perianal inflammation, tears from childbirth, anal intercourse or other trauma, diabetic neuropathy, or neuromuscular disease may result in frequent stools, which may be interpreted by the patient as diarrhea.

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