Red flag	Potential cause
Patient history
associated respiratory symptoms (Children with acute gastroenteritis may have concomitant adenovirus or respiratory syncytial virus (RSV) causing the associated respiratory symptoms)	coronavirus disease (COVID-19)—gastrointestinal symptoms may precede respiratory symptoms leptospirosis anaphylaxis
severe abdominal pain	cause requiring surgical intervention (eg appendicitis, mesenteric ischaemia, perforated viscus, bowel obstruction)—more likely in older patients
upper gastrointestinal bleed (melaena or haematemesis)	Mallory-Weiss tearvaricespeptic ulcer
lower gastrointestinal bleed (bright red rectal bleeding)	bowel cancer diverticulitis ischaemic gut inflammatory bowel disease or colitis
onset of diarrhoea after exposure to an allergen	anaphylaxis
unintentional weight loss	thyrotoxicosis bowel cancer inflammatory bowel disease
vomiting without diarrhoea (in children)	urinary tract infection increased intracranial pressure bowel obstructioncause requiring surgical intervention (eg appendicitis, mesenteric ischaemia, perforated viscus, bowel obstruction)poisoning
recent fish ingestion	ingestion of reef fish and associated neurological symptoms (eg ciguatera fish poisoning)ingestion of fish in Scombroidae family (eg mackerel, bonito) and associated facial flushing (scombroid poisoning)
recent antibiotic use or recent hospitalisation	Clostridioides difficile (formerly known as Clostridium difficile) infection
immunosuppression [patients who are immunocompromised or recent travellers, consider empirical antibiotic therapy]	consider surgical causes (immunosuppression may reduce presence of classical clinical signs)risk for cytomegalovirus (CMV) or parasitic (eg Cryptosporidium species, Cystoisospora [Isospora] belli, microsporidia) infection
recent travel	travellers’ diarrhoea
pregnancy	Listeria monocytogenes infection
history of ulcerative colitis or Crohn disease	exacerbations of inflammatory bowel disease may present with diarrhoea
history of previous abdominal surgery	partial small bowel obstruction
medications	adverse effect of chemotherapy, antibiotics, laxativestoxicity or overdose of lithium, iron, colchicine, organophosphate insecticides withdrawal (eg from opioids)
family history	bowel cancerinflammatory bowel disease
Physical examination
haemodynamic compromise or organ dysfunction	sepsis or septic shock (eg caused by Salmonella species, Escherichia coli, Neisseria meningitidis) gastrointestinal haemorrhage (eg variceal bleed)toxidrome (eg iron overdose)
altered conscious state	increased intracranial pressuresepsis with secondary hypotension
abdominal guarding, rebound tenderness, rigidity or mass	cause requiring surgical intervention (eg appendicitis, mesenteric ischaemia, perforated viscus, bowel obstruction)
significant abdominal distention	subacute bowel obstruction (if vomiting and diarrhoea are present)
bilious vomiting	bowel obstruction
rash	Neisseria meningitidis infection, if nonblanching or purpuric rashleptospirosis, if conjunctival injection also present

Definitions

Acute 

• increase in the frequency of stools or 
• decrease in stool form
• less than 14 days. 
• Most cases of acute infectious diarrhoea are viral, self-limiting and resolve without specific treatment.

Chronic 

• change in normal BM characterized by ↑ volume/ frequency
• ↓ consistency
• duration >4/52 

• Acute Diarrhoeal Illness:
  • 90% infectious causes
  • 10% medications, toxic ingestions, ischaemia etc
• Worldwide:
  • Second most common illness (to common cold)
  • Leading cause of morbidity and mortality worldwide
  • Individuals of all ages; most mortality in children
  • Developing countries (Africa, South-East Asia, Latin America):
    • 10-18 episodes per child, per year
    • 4-6 million deaths per year (12 000 deaths per day!)
    • 50% of deaths in children under 5 years
  • Developed countries
    • 2-3 episodes per child per year
    • much less mortality
  • Mortality
    • Direct:  causes dehydration 
    • Indirect:  causes hypovolemia 🡪 circulatory collapse; causes hypokaliemia and metabolic acidosis; contributes to malnutrition which increases susceptibility to further infections

• Risk Groups for Acute Diarrhoeal Illness:
  • Travelers:
    • Traveler’s Diarrhoea is the most common travel-related illness
    • Mostly short-lived, self-limiting infections
    • 40% of travellers to developing nations
    • Most commonly E. coli, Campylobacter (also Salmonella, Shigella, Rotavirus, Norwalk agent, Giardia)
  • Specific Food Consumers (food poisoning)
    • Seafood:  Hepatitis A, E, Vibrio cholerea, Salmonella
    • Chicken:  Salmonella, Campylobacter, Shigella
    • Raw Meat:  EHEC E. coli
    • Fried Rice:  Bacillus aureus
    • Mayonnaise, cream:  S. aureus, Salmonella
  • Immunocompromised
  • Daycare visitors and their families
  • Institutionalised, eg. Clostridium difficile in hospital

• Epidemics of Severe Diarrhoeal Illnesses:
  • Vibrio cholerae (cholera):
    • Severe watery diarrhoea, if untreated causes dehydration and death
    • Epidemics spread from Ganges valley (India, Bangladesh) eastwards
    • Most recent:
      • 1991= Serotype 01 in Central/South America
      • 1992= Serotype 0139 (also known as “Bengal”) in India and S/E Asia
  • Bacillary Dysentery (bacterial illnesses causing diarrhoea with blood and mucous)
    • Multi-resistant strains of Shigella have caused some epidemics in Bangladesh; others

Differentials

1. Sepsis
2. Pyelonephritis
3. diverticulitis in the elderly
4. ischaemic colitis
5. inflammatory bowel disease
6. irritable bowel syndrome
7. retrocaecal appendicitis 
8. Endocrine disease
9. Drug associated enteritis
10. infective proctitis from receptive anal sex – (eg Neisseria gonorrhoeae, Chlamydia trachomatis) and amoebiasis

Clinical Clues:

• Viral Pathogens:
  • Likely with a history of contact with a person who has acute infectious diarrhoea.
  • Common in outbreaks with secondary cases.
  • Prominent upper gastrointestinal symptoms like vomiting and nausea.
  • Examples: Rotavirus, norovirus, adenovirus, astrovirus.
• Bacterial Aetiology:
  • Likely with fever, tenesmus, and bloody stool.
  • Common in returned travellers with diarrhoea.
  • Examples: Campylobacter enteritis, Clostridioides difficile, Salmonella enteritis, Shigella enteritis.
• Toxin-Mediated Gastroenteritis:
  • Short incubation period (several hours).
  • Closely clustered cases.
  • Symptoms: Vomiting, nausea, abdominal pain.
  • Diarrhoea occurs later.
  • Examples: Staphylococcus aureus, Bacillus cereus.
  • Rarely caused by nonbacterial toxins (e.g., ciguatoxins, tetrodotoxins).

• Immunocompromised Patients:
  • Susceptible to a wide range of pathogens, including bacteria, viruses (e.g., CMV), and parasites (e.g., Cryptosporidium species, Cystoisospora belli, microsporidia).
• Conditions Mimicking Acute Infectious Diarrhoea:
  • Sepsis.
  • Pyelonephritis.
  • Diverticulitis in the elderly.
  • Ischaemic colitis.
  • Inflammatory bowel disease.
  • Irritable bowel syndrome.
  • Retrocaecal appendicitis.
• Special Considerations:
  • In individuals engaging in receptive anal sex, consider infective proctitis caused by sexually transmitted pathogens (e.g., Neisseria gonorrhoeae, Chlamydia trachomatis) and amoebiasis.

Features of viral, bacterial and toxin-mediated acute diarrhoea

Viral	Bacterial	Toxin-mediated
Prominent upper gastrointestinal symptoms such as vomiting and nausea. Typically acute, and resolves within 24 to 48 hours. Often history of contact with a person who has acute infectious diarrhoea (person-to-person transmission). May be part of an outbreak with secondary cases.	Fever, tenesmus and bloody stool. Returned travellers and immunocompromised patients at greater risk. May be associated with recent antibiotic use or hospital admission, which should prompt investigation for Clostridioides difficile.	Vomiting, nausea and abdominal pain are usually prominent symptoms, and diarrhoea, if present, occurs later in the course of illness Short incubation period (typically several hours only). Closely clustered cases.Infections arise from a single point source.

History

• Stool characteristics
  • Water: Chronic Watery Diarrhea
  • Blood, pus or mucus: Chronic Inflammatory Diarrhea/Dysentery
  • Foul, bulky, greasy stools: Chronic Fatty Diarrhea
• Onset (abrupt or gradual)
• Duration
• Frequency of BM
• Severity
  •     mild—the patient is able to undertake normal activities
  •     moderate—the patient is able to function but needs to modify normal activities
  •     severe—the patient is incapacitated and may require admission to hospital.
• Diarrhea pattern
  • Diarrhea alternates with Constipation
    • Colon Cancer
    • Laxative abuse
    • Diverticulitis
    • Functional bowel disorder (Irritable Bowel Syndrome)
  • Intermittent Diarrhea
    • Diverticulitis
    • Functional bowel disorder (Irritable Bowel Syndrome)
    • Malabsorption
  • Persistent Diarrhea
    • Inflammatory Bowel Disease
    • Laxative abuse
• Differentiating Small Bowel from Large Bowel
  • Small Intestine or proximal colon involved
    • Large stool Diarrhea
    • Abdominal cramping persists after Defecation
  • Distal colon involved
    • Small stool Diarrhea
    • Abdominal cramping relieved by Defecation
• Diurnal variation
  • No relationship to time of day: Infectious Diarrhea
  • Morning Diarrhea and after meals
    • Gastric cause
    • Functional bowel disorder (e.g. Irritable Bowel Syndrome)
    • Inflammatory Bowel Disease
  • Nocturnal Diarrhea (always organic)
    • Diabetic Neuropathy
    • Inflammatory Bowel Disease
• Weight Loss
  • Despite normal appetite
    • Hyperthyroidism
    • Malabsorption (e.g. Celiac Sprue, Lactose Intolerance)
    • Giardia
    • Cryptosporidium
    • Cyclospora
  • Associated with fever
    • Inflammatory Bowel Disease
  • Weight loss prior to Diarrhea onset
    • Pancreatic Cancer
    • Tuberculosis
    • Diabetes Mellitus
    • Hyperthyroidism
    • Malabsorption
• Medication and dietary intakes
  • Fementable Oligosaccharides, Disaccharides, Monosaccharides and Polyols (FODMAP)
  • High fructose corn syrup
  • Excessive Sorbitol, Mannitol (chewing gum)
  • Artificial Sweeteners (e.g. Sucralose, chewing gum, fruit juice, soft drinks)
  • Excessive coffee or other Caffeine
  • Alcohol Abuse
  • Illicit Drug use
• Red Flags: Suggestive of organic cause
  • Painless Diarrhea
  • Recent onset in an older patient
  • Nocturnal Diarrhea (especially if wakes patient)
  • Unintentional Weight Loss
  • Blood in stool
  • Large stool volumes: >400 grams stool per day
  • Anemia
  • Hypoalbuminemia

• dysenteric symptoms (ex: Fever, tenesmus, blood/pus in stool)
• symptoms of dehydration
• exposure history
• regular/recent medications
• co-morbidities associated with diarrhoeal illness (eg. GI disease, HIV, carcinoid tumours)
• history of radiation to abdo/pelvis

Examination

1. Vital obs: Temp, postural BP, HR, RR
2. Signs of dehydration: 

	Mild dehydration (<5%)	Moderate dehydration (5-9%) Signs mildly to moderately abnormal	Shock (≥10%) Signs markedly abnormal
Thrust	Frink normally, may be thirsty	thirsty	Drink poortly
Conscious state	Alert and responsive	Lethargic, irritable	Reduced conscious state
Extremities	Warm	Warm	Cold, mottled, cyanosed
Peripheral pulses	Normal	Normal	Weak
Eyes & fontanelle	Not sunken	Sunken	Deeply sunken
Mucous membranes	Moist	Dry	Dry/Parched
Skin turgor *	Instant recoil	Mildly decreased  <2sec	Decreased  >2 sec
Skin colour	Normal	Normal	Pale or mottled
Central capillary refill time *	Normal	Prolonged	Markedly prolonged
urine output	normal or –	– – Yellow/orange colours	– – – or anuric Dark orange/brown
respiratory rate *	normal	normal or +	++, Deep acidotic breathing
pulse rate	normal	+ Tachycardia	++ Tachycardia, weak pulse
blood pressure	normal	mild hypotension or postural hypotension	severe hypotension with peripheral vasoconstriction
* –  most predictive of significant dehydration (more than 5%) in children
+ = slightly increased          ++ = moderately increased         +++ = significantly increased– = slightly decreased        – – = moderately decreased      – – – = significantly decreased
plasma urea	normal	++	+++
plasma creatinine	normal	+	+++
urea:creatinine ratio	normal or +	+++	+++
plasma osmolality	normal	normal	+++
urinary ketones	+	++	+++

Risk factors for dehydration or associated electrolyte abnormalities :

• in adults
  • chronic disease (eg diabetes, chronic kidney disease)
  • kidney transplantation
  • short bowel syndrome or ileostomy
  • immunocompromise
  • pre-existing malnutrition or frailty
  • where there is concern about adherence to treatment or monitoring for dehydration at home
  • intractable or bilious vomiting
  • medications that may cause electrolyte abnormalities (eg diuretics)
  • advanced age
• in children:
  • less than 6 kg (especially preterm infants) or younger than 3 months
  • chronic disease (eg chronic kidney disease, complex congenital cardiac disease)
  • kidney transplantation
  • short bowel syndrome or presence of ileostomy
  • immune compromise
  • pre-existing malnutrition
  • where there is concern about adherence to treatment or monitoring for dehydration at home
  • intractable or bilious vomiting.

3. Mental status
4. Abdo: exclude peritonitis
5. Rectum: for stool character and presence of blood

Severity of Acute Infectious Diarrhoea

Severity Levels

• Mild: Patient can undertake normal activities.
• Moderate: Patient can function but needs to modify normal activities.
• Severe: Patient is incapacitated and may require admission to hospital.

Markers of Severity

• High fever.
• Tachycardia.
• Leucocytosis.
• Abdominal tenderness or severe abdominal pain.
• High-volume diarrhoea with hypovolaemia.
• Bloody stool.
• Prolonged symptoms.

These markers may prompt microbiological testing and consideration of treatment.

Faecal Testing in Acute Infectious Diarrhoea

as per eTG

Indications for Faecal Testing

• Appropriate when results will inform management.
• Recommended for:
  • Patients with bloody stools, moderate to severe disease, or prolonged symptoms.
  • Immunocompromised patients (include tests for parasites and viral pathogens).
  • Situations of public health importance (e.g., outbreaks, residential aged-care facilities, food handlers).

Traditional Faecal Microbiological Testing (M/C/S)

• Methods: Bacterial culture, microscopy, and antigen testing.
• Importance: Enables antimicrobial susceptibility testing and epidemiological assessment.
• Yield: Relatively low compared to mPCR, but positive results are highly diagnostic.
• indiscriminate use of stool cultures in the evaluation of acute diarrhea is inefficient (results are positive in only 1.6% to 5.6% of cases) and expensive, with an estimated cost of $900 to $1,200 per positive stool culture.
• Obtaining cultures only in patients with screening tests positive for leukocytes decreases the cost to $150 per positive culture.
• Obtaining cultures only in patients with grossly bloody stools increases the yield for positive culture results to greater than 30%
• ova and parasites
  • routinely in patients with acute diarrhea is not cost-effective
    • Indications for ova and parasite testing include
      • persistent diarrhea lasting more than seven days
      • especially if associated with infants in day care or travel to mountainous regions
      • diarrhea in persons with AIDS or men who have sex with men
      • community waterborne outbreaks
      • bloody diarrhea with few fecal leukocytes.
    • The benefit of sending multiple samples to increase the test yield is debatable.

CLOSTRIDIUM DIFFICILE TESTING

• recommended for patients who develop unexplained diarrhea after three days of hospitalization
• the test will be positive in 15% to 20% of these patients.
• risk of contracting C. difficile infection increases by seven to 10 times throughout any period of antibiotic treatment and for the first month after antibiotic discontinuation, and this risk is still three times higher in the second and third months after antibiotic discontinuation.

Fecal Calprotectin

• Fecal Calprotectin <40 mcg/g and CRP <0.5 reduce Inflammatory Bowel Disease likelihood to<1%

Culture-Independent Methods (mPCR)

• Advantages:
  • Screens for a broad range of pathogens.
  • Rapid results.
  • Substantially improved yield.
• Disadvantages:
  • Positive result does not necessarily indicate disease.
  • Multiple pathogens often identified—difficult to determine the principal pathogen.
  • Does not enable antimicrobial susceptibility testing.
• Pathogens to Consider
  • Campylobacter enteritis
  • Clostridioides difficile infection
  • Enterohaemorrhagic Escherichia coli enteritis
  • Salmonella enteritis
  • Shigella enteritis
  • Vibrio cholerae (Cholera)
  • Vibrio: Noncholera species
  • Yersinia enterocolitis
  • Cytomegalovirus (CMV) infection
  • Cryptosporidium species
  • Cyclospora cayetanensis
  • Cystoisospora (Isospora) belli
  • Microsporidia

Treatment

Acute infective diarrhoea

1. Education – most cases are self limiting, and management is supportive
2. Oral rehydration
   1. Water. proprietary oral rehydration solutions. fruit juice. sports drinks. Soup. salty crackers
   2. In children
      1. Soft drinks, sports and energy drinks, cordials and fruit juice are not optimal for use as rehydration fluids in children and may cause further deterioration or dehydration if not properly diluted
      2. Oral rehydration solutions should be made up exactly according to instructions
         1. Give frequent small volumes (eg 0.5 mL/kg every 5 minutes)
      3. NG may be required if the child refuses to drink or has frequent vomiting
         1. Nasogastric rehydration is generally well tolerated in preschool-aged children
         2. it can be considered for older children but may not be well tolerated
   3. IV rehydration may be required if:
      1.  have clinical features of severe dehydration
      2.  worsen or do not have a marked response to oral rehydration
      3.  have an associated ileus or ketonaemia.
3. Early refeeding
   1. decreases intestinal permeability caused by infections
   2. reduces illness duration
   3. improves nutritional outcomes.3
   4. BRAT diet (bananas, rice, applesauce, and toast) and the avoidance of dairy are commonly recommended – supporting data for these interventions are limited. 
   5. Instructing patients to refrain from eating solid food for 24 hours also does not appear useful.
4. Simple analgesia for pain & fever
5. Probiotics for acute gastroenteritis
   1. In children :reduce the duration and severity of diarrhoea when given in addition to rehydration therapy, and may be useful adjunctive therapy. Adults = no evidence 
6. Antiemetic drugs
   1. can reduces vomiting
   2. improves intake of oral rehydration solution
   3. reduces the need for intravenous fluids and hospitalisation. 
   4. can worsen diarrhoea (possibly due to retention of fluids and toxins normally eliminated by vomiting).
      1. ondansetron 4 to 8 mg orally, 8- to 12-hourly  OR (child 6 months or older: 0.15 mg/kg up to 8 mg orally)
      2. metoclopramide 10 mg orally, 8-hourly if required
      3. prochlorperazine 20 mg orally, for the first dose, then 10 mg 2 hours later, then 5 to 10 mg 8-hourly if required.
7. Anti- diarrhoeal agents
   1. never indicated for acute diarrhoea in infants and children
   2. In adults with mild or moderate acute diarrhoea, are useful for short-term control of symptoms during periods of social inconvenience (eg travel, work). 

Transient lactose intolerance after gastroenteritis

• Stools commonly remain loose for 1 to 2 weeks after an episode of acute gastroenteritis. 
• Temporary lactose intolerance may occur after gastroenteritis, particularly in infants and young children. Frothy, watery, explosive stools (which may cause perianal excoriation) shortly after drinking milk may indicate lactose intolerance.
• If lactose intolerance is suspected in a child on formula or milk, a temporary change to a lactose-free formula for 2 to 4 weeks may alleviate symptoms.

Empirical Antibiotic Therapy of Acute Infectious Diarrhoea

• acute diarrhea is most often self-limited and caused by viruses
• routine antibiotic use is not recommended for most adults with nonsevere, watery diarrhea. 
• overuse of antibiotics can lead to
  • resistance (e.g., Campylobacter)
  • harmful eradication of normal flora
  • prolongation of illness (e.g., superinfection with C. difficile)
  • prolongation of carrier state (e.g., delayed excretion of Salmonella)
  • induction of Shiga toxins (e.g., from Shiga toxin–producing E. coli)
• Indications:
  • Severe disease
  • Immunocompromised patients
  • Returned travelers – evidence it will shorten duration of illness by 1-3 days

as per eTG

Antibiotic Regimens (If Indicated)

• Ciprofloxacin:
  • 500 mg (child: 12.5 mg/kg up to 500 mg) orally, 12-hourly for 3 days.
• Norfloxacin:
  • 400 mg (child: 10 mg/kg up to 400 mg) orally, 12-hourly for 3 days.
• Azithromycin:
  • 500 mg (child: 10 mg/kg up to 500 mg) orally, daily for 3 days.
• Ceftriaxone (if oral therapy not tolerated):
  • 2 g (child 1 month or older: 50 mg/kg up to 2 g) intravenously, daily for 3 days.

Modification of Therapy

• Based on culture and susceptibility testing results.
• Follow specific treatment guidelines for identified pathogens.

Rehydration and Supportive Measures

• Hydration: Oral rehydration indicated unless severe dehydration requires intravenous therapy.
• Supportive Measures: Include probiotics, antiemetics, antidiarrhoeal drugs, and zinc supplements (see Gastrointestinal guidelines).

Specific Conditions

Campylobacter Enteritis

• Nature:
  • Foodborne zoonosis.
  • Usually self-limited.
  • Rehydration is the mainstay of therapy.
• Antibiotic Therapy Indications:
  • Severe disease (refer to Severity of acute infectious diarrhoea).
  • Third trimester of pregnancy.
  • Infants.
  • Frail elderly.
  • Immunocompromised patients.
• Antibiotic Choices:
  • Azithromycin:
    • 500 mg (child: 10 mg/kg up to 500 mg) orally, daily for 3 days.
  • Ciprofloxacin:
    • 500 mg (child: 12.5 mg/kg up to 500 mg) orally, 12-hourly for 3 days.
    • Note: Not licensed for children due to potential cartilage development issues, but can be used if it is the drug of choice. No oral liquid formulation available.
  • Norfloxacin:
    • 400 mg (child: 10 mg/kg up to 400 mg) orally, 12-hourly for 3 days.
    • Note: Not licensed for children due to potential cartilage development issues, but can be used if it is the drug of choice. No oral liquid formulation available.
• Resistance:
  • Increasing incidence of macrolide- or quinolone-resistant strains.
  • Seek expert advice for resistant infections.
• Contacts:
  • Asymptomatic contacts do not need faecal testing or treatment.

Clostridioides difficile Infection

• Introduction:
  • Causes severe antibiotic-associated diarrhoea.
  • Can occur during or months after antibiotic use.
  • Risk factors: Broad-spectrum antibiotics, hospitalization, cancer chemotherapy, proton pump inhibitors.
• Assessment:
  • Based on clinical features (diarrhoea, ileus, toxic megacolon).
  • Microbiological evidence of toxin-producing C. difficile or pseudomembranous colitis on colonoscopy/histopathology.
  • Sequential testing algorithm: High-sensitivity screening (e.g., PCR) followed by increased specificity test (e.g., EIA).
  • Correlate clinical symptoms with test results to decide on treatment.
  • Colonisation common in children up to 2 years—review positive results carefully.
• Treatment for the First Episode:
  • Mild to Moderate Disease:
    • Metronidazole:
      • 400 mg (child: 10 mg/kg up to 400 mg) orally or enterally, 8-hourly for 10 days.
    • Vancomycin:
      • 125 mg (child: 10 mg/kg up to 125 mg) orally or enterally, 6-hourly for 10 days.
      • Note: Oral vancomycin can be made from injectable form by dissolving in water and measuring the appropriate dose.
• Treatment for First Recurrence or Refractory Disease:
  • Vancomycin:
    • 125 mg (child: 10 mg/kg up to 125 mg) orally or enterally, 6-hourly for 10 days.
  • Fidaxomicin:
    • 200 mg orally, 12-hourly for 10 days.
• Treatment for Second and Subsequent Recurrences or Ongoing Refractory Disease:
  • Faecal Microbiota Transplantation (FMT):
    • Preferred treatment for adults.
  • If FMT not available:
    • Vancomycin:
      • 125 mg orally or enterally, 6-hourly for 14 days.
    • Fidaxomicin:
      • 200 mg orally, 12-hourly for 10 days.
  • Children:
    • Vancomycin:
      • 10 mg/kg up to 125 mg orally or enterally, 6-hourly for 14 days.
    • Nitazoxanide:
      • 1-3 years: 100 mg orally, 12-hourly for 10 days.
      • 4-11 years: 200 mg orally, 12-hourly for 10 days.
      • 12+ years: 500 mg orally, 12-hourly for 10 days.
• Severe Clostridioides difficile Infection:
  • Seek expert advice.
  • Vancomycin:
    • 125 mg (child: 10 mg/kg up to 125 mg) orally or enterally, 6-hourly for 10 days.
  • In complicated cases (e.g., hypotension, shock, ileus, megacolon):
    • Add Metronidazole:
      • 500 mg (child: 12.5 mg/kg up to 500 mg) intravenously, 8-hourly for 10 days.
    • Consider adding intracolonic vancomycin as a retention enema.
• Follow-Up Testing:
  • Only indicated for symptomatic patients.
  • Repeat testing not generally indicated within a month after effective therapy due to prolonged positive results.

Enterohaemorrhagic Escherichia coli (EHEC) Enteritis

• Cause:
  • Shiga toxin-producing strains (e.g., O157, O111).
  • Can lead to haemolytic uraemic syndrome (HUS) or thrombotic thrombocytopenic purpura, particularly in children.
• Treatment:
  • Rehydration is the mainstay of therapy.
  • Antibiotic therapy should not be given to children without fever or sepsis to avoid increasing toxin release and risk of HUS.

Salmonella Enteritis

• Nature:
  • Usually self-limited in otherwise healthy patients without risk factors for complications.
  • Rehydration is the mainstay of therapy.
• Antibiotic Therapy:
  • Not indicated for otherwise healthy patients without risk factors.
  • Indicated for patients with severe disease or at risk of invasive disease/complications:
    • Neonates and children younger than 3 months.
    • Patients with severe diarrhoea, invasive disease, sepsis, or bacteraemia.
    • Patients with prosthetic vascular grafts or haemoglobinopathies.
    • Immunocompromised patients.
• Antibiotic Choices:
  • Azithromycin:
    • 1 g (child: 20 mg/kg up to 1 g) orally on the first day, then 500 mg (child: 10 mg/kg up to 500 mg) orally, daily for a further 4 days.
  • Ciprofloxacin:
    • 500 mg (child: 12.5 mg/kg up to 500 mg) orally, 12-hourly for 5 days.
    • Note: Not licensed for children but can be used if it is the drug of choice. No oral liquid formulation available.
  • Amoxicillin (if pathogen is susceptible):
    • 1 g (child: 30 mg/kg up to 1 g) orally, 8-hourly for 5 days.
• Initial Intravenous Therapy:
  • Ceftriaxone:
    • 2 g (child 1 month or older: 100 mg/kg up to 2 g) intravenously, daily.
    • For septic shock or intensive care: 1 g (child 1 month or older: 50 mg/kg up to 1 g) intravenously, 12-hourly.
  • Ciprofloxacin:
    • 400 mg (child: 10 mg/kg up to 400 mg) intravenously, 12-hourly.

Shigella Enteritis (Shigellosis)

• Nature:
  • Easily transmitted person-to-person.
  • Rehydration is the mainstay of therapy.
• Antibiotic Therapy:
  • Reduces disease transmission and symptom duration by 2 days.
  • Indicated for patients with severe disease and in immunocompromised patients.
  • Also used to reduce transmission in high-risk groups (e.g., children under 6, food handlers, healthcare workers).
• Empirical Therapy:
  • Wait for susceptibility results before starting treatment due to high resistance rates.
  • For severe disease and in immunocompromised patients, use ceftriaxone:
    • 2 g (child 1 month or older: 50 mg/kg up to 2 g) intravenously, daily.

Vibrio cholerae (Cholera)

• Nature:
  • Caused by serotypes O1 and O139.
  • Rare in Australia, mostly acquired overseas or from contaminated water in northern Australia.
  • Rehydration is the mainstay of treatment.
• Antibiotic Therapy:
  • Reduces the volume and duration of diarrhoea.
  • Azithromycin:
    • 1 g (child: 20 mg/kg up to 1 g) orally, as a single dose.
  • Ciprofloxacin:
    • 1 g (child: 20 mg/kg up to 1 g) orally, as a single dose.

Noncholera Vibrio Species Enteritis

• Nature:
  • Caused by Vibrio parahaemolyticus and others, usually from contaminated shellfish.
  • Usually self-limiting.
  • Rehydration is the mainstay of therapy.
• Antibiotic Therapy for Severe/Persistent Disease:
  • Doxycycline:
    • Adults: 100 mg orally, 12-hourly for 10 days.
    • Children 8 years or older: Dosage varies by weight.

Yersinia Enterocolitis

• Nature:
  • Causes acute enterocolitis and other conditions.
  • Postinfectious complications include reactive arthritis and erythema nodosum.
  • Usually foodborne.
• Treatment:
  • Rehydration is the mainstay.
  • Antibiotics not typically indicated for immunocompetent patients.
  • For immunocompromised or persistent/extraintestinal disease:
    • Ciprofloxacin: 500 mg (child: 12.5 mg/kg up to 500 mg) orally, 12-hourly for 5 days.
    • Norfloxacin: 400 mg (child: 10 mg/kg up to 400 mg) orally, 12-hourly for 5 days.
    • Trimethoprim + Sulfamethoxazole: 160+800 mg (child 1 month or older: 4+20 mg/kg up to 160+800 mg) orally, 12-hourly for 5 days.

Antibiotic-Associated Diarrhoea

• Pathogen Identification:
  • Often no pathogen identified.
  • Clostridioides difficile is significant in a minority of cases.
• Management:
  • Stop antibiotics likely causing symptoms if possible.
  • Prophylactic probiotics are widely used, but large trials did not show significant benefit.
  • Immunocompromised patients may rarely develop probiotic-associated bacteraemia.
• Reference:
  • For more details on C. difficile diarrhoea, see Clostridioides difficile infection.

Travellers’ Diarrhoea

• Introduction:
  • Most common illness acquired overseas.
  • Affects 20-50% of short-term travelers from developed to developing areas.
  • Caused by a wide range of pathogens.
  • Common pathogens: Enterotoxigenic Escherichia coli (ETEC), Salmonella, Campylobacter, norovirus.
• Prevention:
  • Precautions in areas with poor water and food hygiene:
    • Select freshly cooked foods served hot.
    • Peelable fruits.
    • Bottled, canned, or recently boiled beverages.
    • Avoid raw/undercooked food, fresh salads, unpasteurised milk, unboiled water, and ice.
    • Avoid roadside vendor foods.
  • Antimicrobial prophylaxis:
    • Early treatment preferred over prophylaxis to avoid resistance.
    • Consider for high-risk travelers (e.g., immunocompromised).
    • Prophylaxis should not exceed 3 weeks.
    • Consider local antibiotic resistance patterns.
• Treatment:
  • Mild Disease:
    • Usually self-limiting.
    • Rehydration is key.
    • Antidiarrhoeal drugs can be used but not recommended for children.
  • Moderate to Severe Disease:
    • Rehydration is essential, especially in young children.
    • Antibiotics are effective and self-treatment is acceptable.
    • Single large dose options:
      • Azithromycin: 1 g (child: 20 mg/kg up to 1 g) orally, as a single dose.
      • Norfloxacin: 800 mg (child: 20 mg/kg up to 800 mg) orally, as a single dose.
      • Ciprofloxacin: 750 mg (child: 20 mg/kg up to 750 mg) orally, as a single dose.
    • Continue antibiotics if fever/bloody stools present or no improvement after single dose:
      • Azithromycin: 500 mg (child: 10 mg/kg up to 500 mg) orally, daily for 2 more days.
      • Norfloxacin: 400 mg (child: 10 mg/kg up to 400 mg) orally, 12-hourly for 2 more days.
      • Ciprofloxacin: 500 mg (child: 12.5 mg/kg up to 500 mg) orally, 12-hourly for 2 more days.
    • Quinolone resistance consideration, especially in South Asia.

Persistent Diarrhoea in Returned Travellers

• Considerations:
  • Both infective and noninfective causes (e.g., postinfectious IBS, lactose intolerance, coeliac disease).
  • Detailed travel and exposure history.
• Investigations:
  • Stool microscopy and culture.
  • Multiple samples for parasitic infections.
  • Serology for certain conditions (e.g., amoebiasis, schistosomiasis).
• Management:
  • Empirical therapy for giardiasis if cause not identified.
  • Seek expert advice if symptoms persist.

Outbreaks of Diarrhoea in Residential Aged-Care Facilities

• Recognition and Control:
  • Early recognition and rapid infection control.
  • Surveillance criteria:
    • Three or more loose bowel motions above baseline over 24 hours.
    • Two or more vomiting episodes over 24 hours.
    • Symptoms in a patient with a detected pathogen.
• Actions:
  • Notify local public health authority if outbreak suspected (more than two cases within 72 hours).
  • Stool samples from symptomatic residents.
  • Consult public health authority for further management.
  • Consider separating unwell residents to prevent spread.
• Management:
  • Same as for other patients with acute infectious diarrhoea.

Pathogen	Source	Incubation	Symptoms	Duration	Treatment	Miscellaneous
BACTERIA (invasive)Dx: stool WBC+, RBC+, C&S
Campylobacter jejuni	Uncooked meat especially poultry	2-10 days	Prodrome of fever, headache, myalgia, and/or malaise precedes diarrhea, abdominal pain & fever.	<1 week	Supportive (macrolide if >1 week or bloody diarrhea)	Most common bacterial cause of diarrhea in Canada
Enteroinvasive E. coli (EIEC)	Contaminated food/water	1-3 days	fever, abdominal pain, tenesmus, scant stool containing mucus & blood	7-10 days	Supportive only, treatment hastens the resolution of symptoms, particularly in severe cases.	Relatively uncommon
Salmonella typhiS. paratyphi(aka. Enteric Fever, Typhoid)	Fecal-oral.Contaminated food/water	10-14 days	Sudden onset crampy abdo pain and diarrhea, prolonged fever (up to 4wks if untreated), headache, rash (“rose spots”)	<5-7 days diarrhea	Empiric treatment with ceftriaxone or azithromycin. fluorquinolone 1st-line if susceptible	Extremes of age, gallstones predispose to chronic carriage increasing quinolone resistance
Non-typhoidal Salmonellosis:S. typhimurium, S. enteritidis	Contaminated animal food products, especially eggs, poultry, meat, milk.	12-72 hrs	Nausea, vomiting, diarrhea, abdo cramping, fever >38oC	3-7 days diarrhea, <72 hrs fever	Supportive.ciprofloxacin – not recommended except in extremes of age, immunosuppression, aneurysms, prosthetic valve grafts/joints.
Shigella dysenteriae	Fecal-oral Contaminated food/water	1-4 days	fever, malaise, anorexia, limited watery diarrhea, progressing to frequent passage of small, bloody, mucopurulent stools	<1 week	ciprofloxacin Antidiarrheals may increase risk of toxic megacolon	Very small inoculum needed for infectionComplications include toxic megacolon, HUS.
Yersinia enterocolitica, Y. pseudotuberculosis	Contaminated food, unpasteurized milk	5 days	Acute diarrhea, low-grade fever, cramping, nausea, vomiting, hematochezia	2 weeks to months	Supportive.Fluoroquinolones only for septicemia, metastatic focal infections, or immunosuppression and enterocolitis.	Majority cases in children 1-4 yrs. Mesenteric adenitis and terminal ileitis forms without diarrhea mimicking appendicitis.
BACTERIA (non-invasive/toxin-mediated)Dx: clinical
B. cereus –    Type A (emetic), (preformed exotoxin)	Rice dishes	1-6 hrs	Nausea, vomiting, cramps	<12 hrs	Symptomatic
B. cereus – Type B (diarrheal)(secondary endotoxin)	Meats, vegetables, dried beans, cereals	8-16 hrs	Large volume watery diarrhea	<24 hrs	Symptomatic
Enterohemorrhagic E. coli (EHEC/STEC)ie: O157:H7	Verotoxin (aka Shiga-like toxin).  Feco-oral,  contamination of hamburger, raw milk, drinking & recreational water.	3-8 days	Grossly bloody diarrhea, fever often absent	5-10 days	SupportiveMonitor renal function. Antibiotics & antidiarrheals may increase risk HUS.	10% develop hemolytic uremic syndrome  (HUS), which, caries 3-5% mortality (especially in children & elderly)
Enterotoxigenic E. coli (ETEC)(colonization of colon + enterotoxin production)	LT and/or ST toxinsContaminated food/water	1-3 days	Watery diarrhea, cramps	3 days	Supportive.loperamide (Immodium®)quinolone or azithromycin.	Number 1 cause of traveller’s diarrhea
Clostridium difficile	Normally present in colon in small numbers		unformed to watery or mucoid stools with characteristic odour.		1st line – Metronidazole (PO/IV), 2nd line – Vancomycin PO	Usually follows antibiotic treatment (especially clindamycin), can develop pseudomembranous colitis
Clostridium perfringens(secondary enterotoxin)	Contaminated food, especially meat and poultry	8-12 hrs	Sudden onset watery diarrhea, cramps, rarely vomiting	<24 hrs	SupportiveAntibiotics not effective as disease is toxin mediated.	Clostridium spores are heat resistant
Staphylococcus aureus(heat-stable preformed exotoxin)	Unrefrigerated meat and dairy products (custard, pudding, potato salad, mayo)	2-4 hrs	Sudden onset severe nausea, cramps, vomiting, prostration	1-2 days	Supportive ± antiemetics
Vibrio cholerae	Contaminated food/water, especially shellfish	1-3 days	painless voluminous diarrhea without abdominal cramps or fever	3-7 days	Aggressive fluid and electrolytes resuscitation. tetracycline or ciprofloxacin	Massive watery diarrhea (1-3 L/d) Mortality <1% with  treatment
PARASITESDx: stool ova and parasites (O&P)
Cryptosporidium	Fecal-oral.	7 days	Non-bloody, watery diarrhea, fever	1-20 days	nitazoxanideparamomycin
Entamoeba histolytica	Worldwide endemic areas Fecal/oral	2-4 weeks	Ranges from asymptomatic to severe grossly bloody diarrhea. Fever, weight loss.	variable	metronidazole + iodoquinol if invasive Only iodoquinol for non-invasive	May resemble IBD. If untreated, potential for liver abscess Sigmoidoscopy shows flat ulcers with yellow exudates.
Giardia lamblia	Fecal-oral (daycare #1).Contaminated food/water (travel related “beaver fever”).	1-4 weeks	Ranges from asymptomatic to acute watery diarrhea with abdo pain to protracted course of flatulence, abdominal distention, fatigue and anorexia	variable	metronidazole. Treatment of asymptomatic carriers not generally recommended	May need duodenal biopsy Higher risk in men who have sex with men (MSM), (MSM), Immunodeficiency (IgA decreased), and  daycares/nurseries
VIRUSES
Rotavirus	Fecal-oral	2-4 days	Watery diarrhea, vomiting, fever	3-8 days	Supportive.Vaccine available, given at 2, 4 & 6 months of age.	Can cause severe dehydration.  Virtually all children are infected by 3 years of age
Norovirus (includes Norwalk virus)	Fecal-oral	24 hrs	nausea, vomiting, abdo cramps, loose watery diarrhea	12-60 hrs	Supportive	Often causes epidemics