Acute Diarrhoea - ICUNOTES

Acute Diarrhoea

1. Definition

Acute diarrhoea = Passage of ≥3 loose/watery stools per day lasting <14 days.

Persistent: 14–28 days
Chronic: >4 weeks

Always clarify duration, volume, blood, travel, antibiotics, immunocompromise, and systemic toxicity.

Acute Diarrhoea vs Dysentery

Feature	Acute Watery	Dysentery
Stool	Watery	Blood + mucus
Fever	Mild	High
Pain	Mild	Severe cramps
Cause	Viral/toxin	Invasive bacteria
Antibiotics	Usually no	Often yes

2. Pathophysiology

Diarrhoea occurs when:

↓ Absorption
↑ Secretion
↑ Osmotic load
↑ Motility
Mucosal inflammation

Types of Acute Diarrhoea

Type	Mechanism	Clinical Clue	Example
Secretory	Active chloride secretion	Large-volume, persists during fasting	Cholera,Post-cholecystectomy,VIPoma
Osmotic	Unabsorbed solute	Improves with fasting	Lactose intolerance,Sorbitol ingestion,Magnesium laxatives
Inflammatory	Mucosal invasion	Blood, fever, tenesmus	Shigella
Motility-related	Rapid transit	IBS-like	Hyperthyroidism

3. Causes of Acute Diarrhoea

A. Infectious (Most Common)

Viral (Most common overall)

Rotavirus – common in children
Norovirus – outbreaks, cruise ships
Adenovirus
Astrovirus

Features:

Watery diarrhoea
Vomiting prominent
Low-grade fever
Self-limiting

Bacterial

Salmonella typhi (Reptiles)
Shigella dysenteriae(Blood/mucus)
Campylobacter jejuni( Poultry)
Vibrio cholerae(Severe dehydration)
Clostridioides difficile(Recent antibiotics)
Enterotoxigenic E. coli (ETEC)(travellers Diarrhea)

Protozoal

Giardia lamblia – greasy stool
Entamoeba histolytica – blood + liver abscess risk
Cryptosporidium – immunocompromised

B. Non-Infectious Causes

Drugs (antibiotics, metformin, magnesium)
Inflammatory bowel disease
Ischaemic colitis
Thyrotoxicosis
Early presentation of coeliac disease

4. Clinical Assessment

1. Watery Diarrhea

Cause	Examples
Viral	Norovirus, Rotavirus
Secretory	Cholera, VIPoma
Osmotic	Lactose intolerance
Endocrine	Hyperthyroidism
Drug-induced	Metformin

2. Bloody Diarrhea

Cause	Examples
Bacterial	Shigella, Campylobacter
IBD	Ulcerative colitis
Ischemic	Mesenteric ischemia
Radiation	Radiation colitis

3. Fatty/Greasy Stool

Cause	Examples
Pancreatic insufficiency	Chronic pancreatitis
Celiac disease	Gluten enteropathy
Giardiasis	Protozoal infection

4. Associated Symptoms

Symptom	Suggestive Diagnosis
Fever	Infection, IBD
Vomiting	Viral gastroenteritis
Tenesmus	Rectal inflammation
Weight loss	Malabsorption, malignancy
Flushing	Carcinoid syndrome
Palpitations	Hyperthyroidism
Arthralgia	IBD
Oral ulcers	Crohn disease
Rash	Celiac disease, IBD

5. Epidemiological History

Travel

Exposure	Organism
Developing countries	ETEC
Hiking/camping	Giardia
Cruise ships	Norovirus

Food History

Food	Organism
Poultry	Campylobacter
Eggs	Salmonella
Seafood	Vibrio
Rice	Bacillus cereus
Cream pastries	Staphylococcus aureus

Water Exposure

Untreated water → Giardia
Flood water → Leptospirosis
Lakes/streams → Cryptosporidium

Sexual History

Consider:

Proctitis
Gonorrhea
Chlamydia
HSV
Syphilis

Immunosuppression

Condition	Pathogens
HIV	Cryptosporidium
Transplant	CMV
Chemotherapy	Opportunistic infections

Abdominal Examination

Finding	Suggests
Diffuse tenderness	Gastroenteritis
RLQ mass	Crohn disease
Rebound tenderness	Perforation
Distension	Toxic megacolon

Extraintestinal Clues

Finding	Diagnosis
Erythema nodosum	IBD
Uveitis	IBD
Dermatitis herpetiformis	Celiac disease
Hyperpigmentation	Addison disease
Thyroid enlargement	Hyperthyroidism

Incubation Period

Incubation	Likely Cause
1–6 hrs	Staph aureus
6–16 hrs	Bacillus cereus
12–48 hrs	Norovirus
2–5 days	Campylobacter
3–4 days	Salmonella
3–8 days	EHEC

History Clue	Likely Cause
Sudden outbreak (school, cruise ship), prominent vomiting, short incubation (12–48 hrs), self-limiting 1–3 days	Norovirus
Infant/child, winter season, daycare exposure, fever + vomiting + watery diarrhoea	Rotavirus
Recent antibiotic use (clindamycin, cephalosporins, fluoroquinolones), hospital stay, foul smell	Clostridioides difficile
Bloody diarrhoea + fever + tenesmus + abdominal cramps	Shigella dysenteriae
Undercooked poultry, severe abdominal pain (may mimic appendicitis), bloody stool	Campylobacter jejuni
Reptile exposure, eggs, poultry, fever prominent, watery ± blood	Salmonella enterica
Typhoid endemic area, step-ladder fever, relative bradycardia,Rose spots, hepatosplenomegaly	Salmonella typhi
Severe dehydration, profuse “rice-water” stools, minimal abdominal pain	Vibrio cholerae
Travel to India/Africa/Latin America, watery diarrhoea, no blood	Enterotoxigenic E. coli (ETEC)
Bloody diarrhoea after undercooked beef, little/no fever,Risk of HUS (esp. children)	Escherichia coli O157:H7
Severe abdominal pain mimicking appendicitis, pork ingestion,Mesenteric lymphadenitis	Yersinia enterocolitica
Rapid onset vomiting (1–6 hrs after cream pastries, buffet food), minimal diarrhoea	Staphylococcus aureus
Fried rice reheated, vomiting predominant (6 hrs) OR diarrhoea predominant (8–16 hrs)	Bacillus cereus
Greasy, Steatorrhoeafoul-smelling stool, bloating, after camping/stream water	Giardia lamblia
Bloody diarrhoea + liver abscess risk, travel to tropics	Entamoeba histolytica
Immunocompromised (HIV), watery diarrhoea, no blood	Cryptosporidium

5. Investigations

No Routine Testing Needed

Healthy adult with:

Mild watery diarrhea
<7 days
No fever
No blood
No dehydration

When required

Bloody diarrhoea
Severe dehydration
Hypotension
Elderly (>65)
Immunocompromised
Persistent >7 days
Recent antibiotics
Recent hospital admission
Suspected outbreak
Severe abdominal pain

1. Full Blood Count (FBC)

Finding	Suggests
Neutrophilia	Bacterial infection
Leukopenia	Severe sepsis / viral
Thrombocytopenia	Sepsis / HUS
Anaemia	Chronic bleeding / HUS

Thrombocytopenia + AKI + haemolysis → Think EHEC → HUS.

2. Urea & Electrolytes (U&E)

Essential in moderate–severe cases

Look for:

↑ Urea → dehydration
Hypokalaemia → diarrhoeal losses
Metabolic acidosis → bicarbonate loss
AKI

3. CRP

High CRP → inflammatory diarrhoea
Normal CRP → viral more likely

4. Blood Cultures

Indicated if:

High fever
Systemic toxicity
Immunocompromised
Suspected typhoid

Important in:

Salmonella typhi
Severe Salmonella enterica

5. STOOL EVALUATION

Stool Examination

Test	Utility
Stool microscopy	Ova, parasites
Fecal leukocytes	Inflammatory diarrhea
Occult blood	Colitis
Fecal calprotectin	IBD marker
Stool culture	Bacterial pathogens
C. difficile assay	CDI
Multiplex PCR panel	Rapid pathogen detection

Stool Microscopy Findings

Finding	Diagnosis
RBCs	Invasive diarrhea
WBCs	Colitis
Giardia cysts	Giardiasis
Entamoeba trophozoites	Amebiasis

STOOL OSMOTIC GAP

Useful in chronic watery diarrhea.

Formula-Stool Osmotic Gap= 290 − 2 × (Stool Na + Stool K)

Gap	Interpretation
<50 mOsm/kg	Secretory
>100 mOsm/kg	Osmotic
50–100	Mixed

When to Send Stool Culture?

According to current infectious diarrhea guidelines:

Send stool culture if:

Indication

Bloody diarrhea

Severe illness

High fever

Sepsis

Immunocompromised

Persistent diarrhea

Outbreak investigation

Stool for Shiga Toxin

Important if:

Bloody diarrhoea
Minimal fever
Children
Suspected EHEC

Organism:

Escherichia coli O157:H7

Avoid antibiotics in suspected EHEC (risk of HUS).

6. CT Abdomen Indicated If:

Severe abdominal pain
Suspected:

Toxic megacolon
Ischaemic colitis
Perforation

Common in:

Severe Clostridioides difficile
Elderly with vascular disease

7. Endoscopy

Colonoscopy Indications

Indication

Chronic diarrhea

Blood in stool

Weight loss

Iron deficiency anemia

Elevated calprotectin

Suspected IBD

Age >50 with alarm symptoms

Management

STEP 1: Assess Severity (Always First)

Finding	Mild	Moderate	Severe
Thirst	+	++	+++
Dry mouth	Mild	Moderate	Severe
Pulse	Normal	Tachycardia	Marked tachycardia
BP	Normal	Normal	Low
Urine	Slightly reduced	Reduced	Minimal/anuria
Mental status	Normal	Irritable	Lethargic

If unstable → Resuscitate first (ABCDE).

Admission Criteria

Severe dehydration
Electrolyte imbalance
AKI
Elderly/frail
Immunocompromised
Suspected surgical abdomen

FLUID MANAGEMENT

A. Mild–Moderate Dehydration

Oral Rehydration Solution (ORS)

First-line in almost all patients
WHO-type balanced glucose-electrolyte solution

Mechanism:

Glucose enhances sodium absorption via SGLT1 → water follows

Encourage:

Small frequent sips
Continue feeding

WHO ORS:

Component	Amount
Sodium	75 mmol/L
Glucose	75 mmol/L
Osmolarity	245 mOsm/L

Rehydration Dose

Degree	ORS Dose
Mild dehydration	50 mL/kg over 4 h
Moderate dehydration	75–100 mL/kg over 4 h

Ongoing Losses

Add:200–250 mL ORS after each loose stool

B. Severe Dehydration

IV Fluids

balanced crystalloid
20–30 mL/kg boluses if hypotensive
Monitor electrolytes

Correct:

Hypokalaemia
Metabolic acidosis

NUTRITION

Continue normal diet
Avoid prolonged fasting
Avoid excessive fruit juice (osmotic diarrhoea)
Avoid High-fat meals

No need for “BRAT diet” routinely in adults.

ANTIDIARRHOEAL DRUGS

Loperamide-4 mg initially then 2 mg after each stool(Maximum-16 mg/day)

Indications:

Mild watery diarrhoea
No blood
No fever

Mechanism:

μ-opioid receptor → ↓ gut motility

Avoid if:

Bloody diarrhoea
Suspected invasive bacterial infection
Suspected C. diff

ANTIBIOTICS – SELECTIVE USE ONLY

Most acute diarrhoea = viral → NO antibiotics.

Case	Clinical Clues / Likely Pathogens	Recommended Empiric Antibiotic Regimen
Severe Dysentery	Bloody diarrhea + Fever ≥38.5°C + Severe abdominal pain + Toxic appearance; likely Shigella, Campylobacter, Salmonella	Azithromycin 1 g PO once OR 500 mg PO daily × 3 days (preferred); Alternative: Ciprofloxacin 500 mg PO BD × 3 days
Severe Traveler’s Diarrhea	≥6 stools/day, fever, bloody stools, severe dehydration; especially travel to South Asia where fluoroquinolone resistance is common	Azithromycin 1 g PO single dose OR 500 mg PO daily × 3 days (preferred guideline regimen)
Suspected Cholera	Massive rice-water stools, severe dehydration, epidemic/outbreak setting; antibiotics given after aggressive rehydration	Azithromycin 1 g PO once (preferred) OR Doxycycline300 mg PO once; reduces stool volume, duration, and bacterial shedding
Immunocompromised Patient with Acute Diarrhea	Neutropenia, transplant recipient, advanced HIV, chemotherapy patient plus fever, systemic toxicity, or bloody diarrhea	Start empiric therapy while investigations are pending: Ciprofloxacin 500 mg PO BD or Ceftriaxone 2 g IV once daily
Suspected Enteric Fever (Typhoid)	Persistent fever, abdominal pain, diarrhea or constipation, relative bradycardia	Ceftriaxone 2 g IV once daily or Azithromycin 1 g loading dose then 500 mg PO daily
Sepsis Due to Enteric Infection	Septic shock, severe sepsis, Salmonella bacteremia, severe enteric fever, neutropenic enterocolitis	Immediate broad-spectrum IV therapy: Ceftriaxone 2 g IV daily; Piperacillin-Tazobactam 4.5 g IV every 6–8 h; Carbapenem (e.g., Meropenem 1 g IV every 8 h) if ESBL risk or severe MDR infection suspected

When NOT to Give Antibiotics

Mild viral gastroenteritis
Suspected EHEC (risk of HUS)

Escherichia coli O157:H7 Reason:Antibiotics increase risk of: Hemolytic Uremic Syndrome

C. difficile Diarrhea

Complications

Dehydration
Electrolyte imbalance
Acute kidney injury
Haemolytic uraemic syndrome (EHEC)
Reactive arthritis (Campylobacter)
Guillain–Barré syndrome

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