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  • Acute diarrhea: lasts < 2 weeks.

  • Chronic diarrhea: lasts > 2 weeks.

  • Mild diarrhea: ≤ 3 stools per day.

  • Moderate diarrhea: ≥ 4 stools per day with local symptoms (abdominal cramps, nausea, tenesmus).

  • Severe diarrhea: ≥ 4 stools per day with systemic symptoms (fever, chills, dehydration).


Acute diarrhea can be caused by a number of different factors, including emotional stress, food intolerance, inorganic agents (eg, sodium nitrite), organic substances (eg, mushrooms, shellfish), medications, and infectious agents (including viruses, bacteria, and protozoa) (Table 30–3). From a diagnostic and therapeutic standpoint, it is helpful to classify infectious diarrhea into syndromes that produce inflammatory or bloody diarrhea and those that are noninflammatory, nonbloody, or watery. In general, the term “inflammatory diarrhea” suggests colonic involvement by invasive bacteria or parasites or by toxin production. Patients complain of frequent bloody, small-volume stools, often associated with fever, abdominal cramps, tenesmus, and fecal urgency. Common causes of this syndrome include Shigella, Salmonella, Campylobacter, Yersinia, invasive strains of Escherichia coli, and other Shiga-toxin–producing strains of E coli (STEC), Entamoeba histolytica, and C difficile. Tests for fecal leukocytes or the neutrophil marker lactoferrin are frequently positive, and definitive etiologic diagnosis requires stool culture. Noninflammatory diarrhea is generally milder and is caused by viruses or toxins that affect the small intestine and interfere with salt and water balance, resulting in large-volume watery diarrhea, often with nausea, vomiting, and cramps. Common causes of this syndrome include viruses (eg, rotavirus, norovirus, astrovirus, enteric adenoviruses), vibriones (Vibrio cholerae, Vibrio parahaemolyticus), enterotoxin-producing E coli, Giardia lamblia, cryptosporidia, and agents that can cause food-borne gastroenteritis. In developed countries, viruses (particularly norovirus) are an important cause of hospitalizations due to acute gastroenteritis among adults.

Table 30–3.Acute bacterial diarrheas and "food poisoning" (listed in alphabetical order).

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