Treatment Guideline Chart
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, fungal) and is usually associated with symptoms of nausea and vomiting, abdominal cramps and fever.
Dysentery (invasive diarrhea) has the presence of visible blood in diarrheic stool.

Diarrhea%20in%20adults%20-%20infectious Diagnosis


  • 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 and the presence of complications or comorbid conditions 
    • It is more important to consider the change in stool consistency rather than the change in stool frequency in the evaluation of a patient with diarrhea  
  • 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 beats per minute (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

Clinical Presentation of Mild Dehydration

  • Patient is alert, active, up and about
  • Able to perform daily activities without difficulty

Clinical Presentation of Moderate Dehydration

  • Patient is usually weak or lethargic, irritable, restless, but able to walk or sit; thirst is increased; urine output is reduced
  • Able to perform daily activities but with limitations (eg not able to work)
  • Patient is usually tachycardic with normal or slightly decreased systolic blood pressure (SBP) and may or may not have postural hypotension
  • Jugular venous pressure is normal or slightly flat, mucosa is slightly dry, there is a fair amount of skin turgor and eyeballs are only minimally sunken

Clinical Presentation of Severe Dehydration

  • Patient is inactive, unable to sit or walk, has decreased consciousness, unable to drink with minimal urine output
  • Unable to perform daily activities, patient stays in bed or needs hospitalization
  • Patient is tachycardic, SBP is decreased by >20 mmgHg and postural hypotension is present
  • Jugular veins are flat, mucosa is severely dry, skin turgor is poor and eyeballs are visibly sunken


  • Management of acute gastroenteritis in adults may be decided upon the history and presentation
    • Fever, vomiting and abdominal pain are sensitive symptoms for diarrhea caused by Campylobacter, E coli, Salmonella, Shigella and rotavirus

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 3-7 days and resolves even without treatment
  • Further work-up is required if there is fever or bloody stool
  • Further work-up is required if there is fever or bloody stool
    • Evaluation for parasitic infection is recommended if lasting ≥14 days

Classification of Acute Traveler's Diarrhea According to Functional Impact

  • Mild diarrhea: Characterized by ≤3 loose bowel movements per day or diarrhea that is bearable, not distressing and patient is able to travel or engage in other activities as scheduled
  • Moderate diarrhea: Characterized by ≥4 bowel movements per day or diarrhea that is distressing or interferes with patient's travel plans or activities
  • Severe diarrhea: Characterized by ≥6 bowel movements per day or diarrhea which is incapacitating or interferes with patient's daily activities and prevents planned trips or other activities
    • Bloody diarrhea (dysentery) is considered severe


  • Causes of acute traveler's diarrhea will vary from one geographical area to another
  • Bacteria are responsible for 80-90% of cases, parasites in 10%, and viruses in 5-8% of cases
  • Toxigenic E coli is one of the most frequently identified organisms
  • Campylobacter infections seem to predominate as the cause of traveler's diarrhea in North Africa and Southeast Asia
  • Other common organisms:
    • Enteroaggregative E coli, Salmonella, Shigella spp and viruses (eg rotavirus and the Norwalk agent)
  • Parasites should be considered in diarrhea that lasts >7 days
    • Please see Parasitic Infections disease management chart for further information

Watery Diarrhea

  • Semi-formed to loose-watery stools without 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
  • 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


  • 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)

Bloody Diarrhea

  • Macroscopic exam of stool contains blood
  • 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 moderate to severe abdominal cramps and tenesmus


  • 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, Clostridioides difficile, enterohemorrhagic E coli (EHEC), enteroinvasive E coli (EIEC), rotavirus and norovirus can also produce bloody diarrhea

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 or pus in stool, are febrile, dehydrated or immunocompromised, with severe abdominal tenderness or cramping, persistent diarrhea, suspected nosocomial infection, or signs of sepsis
  • Serum creatinine and electrolyte levels should be taken in cases of dehydration or systemic toxicity
    • Other lab tests to be done if complications are suspected include a CBC, urinalysis, BUN, serum bicarbonate, total CO2 or arterial blood gas 

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 Clostridioides 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 obtained within 3 days of hospital admission and before antibiotic therapy, and 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
  • High risk of complications

Blood Cultures

  • Recommended for:
    • Patients of any age with signs of sepsis
    • Suspicion of enteric fever
    • Patients with systemic infectious symptoms
    • Immunocompromised patients
    • Patients with high-risk conditions such as hemolytic anemia
    • Patients with high-grade fever of unknown etiology and with history of travel or had contact with travelers from enteric fever-endemic areas
Editor's Recommendations
Special Reports