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.

Rehydrate and Maintain Hydration

  • Maintenance of adequate intravascular volume and correction of fluid and electrolyte imbalance take precedence over identification of causative agent
  • Sports drinks are inappropriate for patients with diarrhea and commercial juices or carbonated drinks containing simple carbohydrates at high concentrations should not be given

Clinical Presentation of Mild Dehydration

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

Rehydration in Mild Dehydration

Oral Rehydration Therapy (ORT)

  • The standard for cost-effective management of acute gastroenteritis
    • Consists of both rehydration and maintenance fluid therapy
  • Patients with mild dehydration and little or no vomiting may be rehydrated orally with oral rehydration salts solution (ORS)
    • ORS should be given at 1.5 x the volume of stool loss in 24 hours without stopping dietary intake
    • If vomiting is severe and fluids cannot be replaced orally, Ringer’s lactate may be given IV
  • Many oral rehydration formulas are available. Please see the latest MIMS for available formulations

Oral Rehydration Salts Solution (ORS)

  • Achieves optimal oral fluid replacement for moderate-severe dehydration
  • May also be used in those with mild dehydration along with intermittent free water intake
    • Given after each loose stool (120-240 mL) up to 2 L in 24 hours
  • ORS formula that is recommended by the World Health Organization (WHO)
    • 75 mmol/L Na, 20 mmol/L K, 65 mmol/L Cl, 10 mmol/L Citrate, 75 mmol/L Glucose (anhydrous)
    • Produces less vomiting and diarrhea than standard ORS and decreases the need for IV therapy
    • Recommended in all age groups and types of diarrhea including cholera 
  • Rice-based ORS may be used for patients with cholera whenever its preparation is convenient
  • Home-made oral fluid solution may be an option
    • Mixture of 1-L clean (boiled then cooled) drinking water plus 1 tsp of salt and 8 tsp of sugar

Clinical Presentation of Moderate Dehydration

  • Patient is usually weak or lethargic, irritable, restless, but able to walk or sit; thirst is increased
  • Able to perform daily activities but with limitations (eg not going 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 reduced urine output
  • Unable to perform daily activities, patient stays in bed or needs hospitalization
  • Patient is tachycardic, SBP is decreased by >20 mmHg and postural hypotension is present
  • Jugular veins are flat, mucosa is severely dry, skin turgor is poor and eyeballs are visibly sunken

Rehydration in Moderate to Severe Dehydration

IV Therapy

  • Patients who present with severe dehydration or hypovolemic shock should be treated promptly with aggressive IV fluid replacement, if available
    • Ringer’s lactate is preferred since it contains 4 mEq/L of K
    • If Ringer’s lactate is unavailable, normal saline may be an alternative in all age groups
  • Patients with less severe dehydration but with vomiting or inability to tolerate orals can be given IV fluid replacement
  • In patients with moderate-severe dehydration, at least half of the calculated loss should be replaced within 4 hours and the rest within 24 hours
  • Total fluid deficit in severely dehydrated patients can be replaced within the 1st 4 hours of therapy, half within the 1st hour
  • Assessment of fluid and electrolyte deficit is important in order to calculate the amount to replace
    • Stool volume loss should be closely observed and if possible, weighed or measured


  • Antidiarrheals may assist in reducing amount of fluid loss, frequency and consistency of the stool and shorten the clinical course of diarrhea
    • Not recommended for cholera


  • Useful in mild-moderate secretory diarrhea by decreasing the frequency and volume of stools
  • Avoid administering these drugs in patients with evidence of invasive enteritis (eg high fever, chills, bloody diarrhea, abdominal pain)
    • These agents may induce intestinal stasis and may enhance tissue invasion by the organism or delay their clearance from the bowel


  • Most commonly recommended agent for treating acute uncomplicated diarrhea
  • Loperamide has antimotility and antisecretory properties


  • Not considered as effective as Loperamide and may cause cholinergic side effects
  • Fluid replacement is highly encouraged as this may mask volume of lost fluids

Intestinal Adsorbents

  • Appear to have some benefit in traveler’s diarrhea, are well tolerated and safe to use in pregnancy
  • Not effective in patients with febrile bloody diarrhea
  • Eg Attapulgite, Activated charcoal, Kaolin, Pectin, Dioctahedral smectite
  • In theory, may adsorb toxins produced by toxigenic bacteria and act by preventing their adherence to the intestinal membrane
    • Efficacy, therefore, depends on early administration prior to toxins adhering to intestinal wall
    • Renders a more formed stool, but does not reduce the net loss of water and electrolytes

Bismuth Preparations

  • May be given in patients with fever and dysentery
  • Bismuth subsalicylate has antisecretory, antibacterial and anti-inflammatory effects
  • Reduce the number of stools passed and the duration of diarrhea by about 50%
    • May interfere with absorption of other drugs (eg Doxycycline)

Empiric Therapy

  • Empiric therapy is indicated for:
    • Moderate to severe traveler’s diarrhea
    • Invasive bacterial diarrhea with fever and bloody stools in the absence of EHEC
    • High-risk patients (eg immunocompromised and elderly)
    • Hospital- or antibiotic-associated diarrhea
    • Epidemics

Traveler’s Diarrhea

Empiric antibiotic treatment for traveler’s diarrhea has been the best approach, but its usefulness is being undermined by growing antibiotic resistance in many parts of the world

General Therapy Principles

  • The objective of antimicrobial therapy for treatment of traveler’s diarrhea is shortening illness and returning travelers to normal activities
  • Eradication of enteropathogens from stool does not predict the clinical benefits of antimicrobial therapy
  • Traveler’s diarrhea is typically short-lived and self-limited, but many organisms that cause the infection can be treated with antibiotics
  • Choice of therapy should depend on epidemiologic data


  • Causes of acute traveler’s diarrhea will vary from one geographical area to another
  • 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
  • See Parasitic Infections Disease Management Chart for details


  • Should be considered in areas where Campylobacter resistance to quinolones has become problematic
  • Reported effective against traveler’s diarrhea in Southeast Asia, where C jejuni is a common cause of diarrhea and quinolone-resistant Campylobacter sp are common
  • May be used in children


  • Typically considered the treatment of choice for acute diarrhea in adult travelers but resistant organisms are becoming an issue especially in Southeast Asia


  • Approved by United States Food and Drug Administration (USFDA) for treatment of traveler’s diarrhea caused by noninvasive strains of E coli
  • Has been shown to be effective in traveler’s diarrhea cases in Mexico, Kenya and Jamaica
  • Rifaximin is not absorbed from the GI tract and therefore may not be effective against invasive organisms eg Shigella or Campylobacter spp

Duration of Therapy

  • Three days of antibiotic treatment is recommended (except for Azithromycin taken as a single dose)
  • Reevaluate the patient after 24 hours of antibiotic treatment
    • If no improvement is evident, continue to complete 3 days of antibiotic treatment
    • If patient is well after 24 hours from beginning of antibiotic therapy, may consider stopping the therapy sooner


  • Rehydration and antibiotics are the mainstay of therapy
  • When antibiotics are administered to cholera patients, there is reduction of stool volume loss and a shorter clinical course
    • Antibiotics administered should follow local epidemiological and recent sensitivity data for Vibrio cholerae, if available
  • First-line agents Azithromycin, Tetracycline, Doxycycline or Ciprofloxacin may be used if sensitivity data is not known
    • If with Tetracycline resistance, may consider Erythromycin ethylsuccinate, Azithromycin or Ciprofloxacin
  • Co-trimoxazole [Sulfamethoxazole (SMZ) and Trimethoprim (TM)] is a 2nd-line agent
  • Duration of therapy: 3 days except for Azithromycin, Doxycycline, and Ciprofloxacin which are all taken as single doses

Bloody Diarrhea

  • Treat the mild dehydration with ORT
  • Antipropulsives should be avoided as these drugs may increase the severity by delaying excretion of organisms and facilitating invasion of the mucosa
  • Empiric antibiotics can reduce the duration of illness and shorten the carrier stage
  • Once EHEC or Shiga toxin-producing E coli (STEC) has been excluded by stool exam, empiric therapy with antibiotics can be started
  • Antibiotics following the local sensitivities for Shigella sp may be used as empiric therapy while waiting for culture and sensitivity results
  • If local sensitivities are not known, one of the following empiric antibiotics may be used: Ciprofloxacin (drug of choice), Levofloxacin, Norfloxacin
  • Duration of therapy: 3 days

Pathogen-Specific Antibiotic Treatment

  • In most cases, antimicrobial therapy is not required since diarrhea is usually self-limited; however, therapy with empiric and specific antibiotics may be given in certain situations:
    • Severe cholera and shigellosis
    • Dysenteric form of campylobacteriosis and nontyphoidal salmonellosis 
  • Choice of antimicrobial therapy should depend on local susceptibility patterns

Aeromonas/Plesiomonas spp

  • Antibiotics not usually required
  • Aeromonas sp: Antibiotics may be indicated in patients prone to septicemia (eg cirrhosis, immunocompromised patients)
  • Plesiomonas sp: Antibiotics may be required in severely ill or immunocompromised patients
  • First-line agents: Quinolones
  • Duration of therapy: 3 days

Campylobacter sp

  • Antibiotics not usually required; may be used in severely ill patients or traveler’s diarrhea
  • First-line agent: Azithromycin
  • Second-line agents: Quinolones
  • Duration of therapy: 3 days

E coli 0157:H7 (enterohemorrhagic, EHEC)

  • Avoid antipropulsives and antibiotics

Salmonella (non-typhi) sp

  • Antibiotics recommended in severe illness, when patient is septic or hospitalized
    • Usually, no treatment in asymptomatic or mild illness
  • First-line agents: Quinolones
  • Second-line agents: Ceftriaxone, Co-trimoxazole [Sulfamethoxazole (SMZ) and Trimethoprim (TM)], Azithromycin
  • Duration of therapy: 5-7 days
  • Ceftriaxone may be considered in suspected septicemic cases
  • Co-trimoxazole should only be used if organism is susceptible

Shigella sp

  • First-line agents: Quinolones
  • Second-line agents: Azithromycin, Co-trimoxazole [Sulfamethoxazole (SMZ) and Trimethoprim (TM)], Nalidixic acid, Pivmecillinam, Ceftriaxone
  • Duration of therapy: 3 days except for Azithromycin, Nalidixic acid, Pivmecillinam, and Ceftriaxone which are for 5 days

Yersinia sp

  • Antibiotics not usually required; may be used in severely ill patients, bacteremia or immunocompromised hosts
  • Abdominal pain caused by mesenteric adenitis can mimic pain of acute appendicitis
  • First-line agents: Doxycycline plus Tobramycin or Gentamicin
  • Second-line agent: Co-trimoxazole [Sulfamethoxazole (SMZ) and Trimethoprim (TM)]
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