Diarrhea is a change in normal bowel movements characterized by increased frequency, water content or volume of stools.
Infectious diarrhea is diarrhea of infectious origin (bacteria, virus, protozoal) and is usually associated with symptoms of nausea and vomiting and abdominal cramps.
Dysentery (invasive diarrhea) has the presence of visible blood in diarrheic stool.


  • Initial clinical evaluation of the patient with acute diarrhea should focus on assessment of the severity of the illness, the need for rehydration and the identification of likely causes on the basis of history and clinical findings
  • A careful clinical evaluation is needed in order to provide a cost-effective evidence-based approach to initial diagnostic tests and treatment
  • A diagnostic evaluation is warranted in patients with bloody diarrhea, relatively severe illness, and who are high risk (immunocompromised or elderly)

Physical Examination

  • Focus on evaluating the patient’s hydration status

Vital Signs

  • Pulse rate >90 bpm
  • Absence of palpable pulse
  • Postural or supine hypotension
  • Presence of fever

Other Signs of Volume Depletion

  • Dry mucous membranes
  • Sunken eyeballs
  • Decreased skin turgor
  • Absent jugular venous pulsation
  • Altered sensorium


  • Management of acute gastroenteritis in adults may be decided upon the history and presentation

Toxin-Induced Food Poisoning or Viral Gastroenteritis

  • Should be suspected in those with vomiting as the major presenting symptom

Bacterial Toxin-Induced Food Poisoning

  • Incubation period is usually 6-24 hours
  • Diarrhea occurs 2-7 hours after eating the contaminated food
  • Diarrhea may follow vomiting and is usually not so severe
  • Abdominal pain may also be present and is usually colicky in nature
  • Most patients are afebrile and not severely dehydrated unless vomiting or diarrhea is intense

Viral Gastroenteritis

  • Caused by rotavirus, human caliciviruses, adenovirus serotype 40/41, norovirus
  • Incubation period is usually between 18-72 hours
  • Characterized by the abrupt onset of nausea and abdominal cramps followed by vomiting and/or diarrhea
  • Low-grade fever (above 37.5°C) develops in about half of affected individuals
  • Headache, myalgia, upper respiratory tract symptoms and abdominal pain are common
  • Illness is usually mild and self-limiting, lasting 24-48 hours

Traveler’s Diarrhea

  • Usually considered in a person who normally resides in an industrialized region and who travels to a developing country or a person from a developing country who travels to an industrialized region
  • May also refer to illness that occurs within 7-10 days after returning home
  • Prodromal symptoms include N/V, cramping abdominal pain and fever
  • Usually lasts 3-5 days and resolves even without treatment
  • Further work-up is required if there is fever or bloody stool
  • Bacteria are responsible for 80-90% of cases, parasites in 10%, and viruses in 5-8% of cases

Watery Diarrhea

  • Semi-formed to loose-watery stools witho the presence of blood
  • Often clinical presentation of enterotoxin-induced diarrhea; most common causative agent is enterotoxigenic E coli (ETEC) in a non-epidemic situation


  • Severe dehydration with severe watery diarrhea is most likely caused by Vibrio cholerae subgroup O1
  • Vibrio O139, other non-O1 vibrios and occasionally Vibrio parahaemolyticus, Aeromonas sp and enteropathogenic Escherichia coli can cause a similar clinical picture (though diarrhea by these organisms is usually milder)
  • Cholera
    • Associated with epidemic diarrhea, it is highly suggested by severe, profuse, watery diarrhea and dehydration
    • Other clinical features: Very abrupt onset of acute diarrhea with rapid progression to severe dehydration, presence of muscle cramps and vomiting but no fever or abdominal pain
    • Stools are usually watery, mucoid and colorless with little food residue
    • Stool microscopy and stool culture should be done in all cases
    • If cholera is confirmed in nonendemic areas, it should be reported to health authorities
    • Any case of watery diarrhea in cholera-endemic areas during outbreaks or seasonal epidemics should be treated as cholera and stool cultures should be done in all cases to confirm

Bloody Diarrhea

  • Macroscopic exam of stool contains blood


  • Shigella spp: Most common cause of acute bloody diarrhea
    • S dysenteriae and S flexneri may cause a more severe disease with high fever, the former producing Shiga toxin
    • S boydii and S sonnei cause a milder disease
  • Campylobacter jejuni infection is suggested by a history of exposure to cattle and poultry and the presence of animals near the patient’s cooking area
  • Salmonella enteritidis, Yersinia enterocolitica, Clostridium difficile, enterohemorrhagic E coli (EHEC) and enteroinvasive E coli (EIEC) can also produce bloody diarrhea

Clinical Presentation

  • Patients often have fever that may last >2 days and may be high (>38.5°C)
  • May initially suffer with watery diarrhea that rapidly changes to dysentery
  • Mild dehydration
  • Dysentery
    • Suggested by frequent passage (10-30 times per day) of small-volume stools that consist of blood, mucus and pus
    • Patient usually suffers abdominal cramps and tenesmus

Laboratory Tests

  • Lab studies are not usually needed but may be helpful in epidemics in etiology identification
  • Many diarrheal illnesses are viral or self-limiting and will resolve in <1 day; therefore, microbiological testing is not typically required in patients who present <24 hours after the onset of diarrhea
    • Exception: Patients who present with blood, pus in stool, are febrile or dehydrated
  • Serum creatinine and electrolyte levels should be taken in cases of dehydration or systemic toxicity

Stool Exam

  • Stools typical of cholera are watery, mucoid and colorless with little food residue (rice-watery stools)
  • Bloody mucoid diarrhea is characteristic of EIEC infection, while EHEC produces bloody diarrhea with hemorrhagic colitis and hemolytic uremic syndrome in 6-8%

Stool Microscopy

  • Performed in cases of persistent or severe bloody diarrhea
  • Viral gastroenteritis: Red and white cells are not normally found
  • Cholera: May reveal bacteria with darting motility but no WBC or RBC
  • Yersinia enterocolitica and Clostridium difficile produce heme-positive stool
  • No fecal WBC is seen with EHEC infection
  • Fecal WBCs are present in 80-90% of diarrhea caused by Shigella or Salmonella and are less common with those caused by Campylobacter and Yersinia

Stool Culture/Sensitivity

  • Not necessary for all cases of diarrhea unless a bacterial cause is suspected
  • Should be performed in both non-endemic and endemic areas

Specific Indications

  • Bloody stools or those that are positive for occult blood or leukocyte
  • Prolonged diarrhea not previously treated with antibiotics
  • Immunocompromised host
  • For epidemiologic purposes (eg cases involving food handlers)
  • Need for early testing
    • Patient is >70 years old
    • with severe abdominal pain
    • C difficile-associated disease is suspected
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