Acute Diarrheal Disease

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Introduction

  • Acute diarrheal disease is a significant global health issue that can result from various infectious agents, including bacteria, viruses, and parasites.
  • It is characterized by the sudden onset of diarrhea, which can lead to dehydration and, in severe cases, death, particularly among vulnerable populations such as children and the elderly.
  • Timely and accurate laboratory diagnosis is essential for determining the cause of the diarrhea, guiding appropriate treatment, and implementing effective public health measures.

 

Epidemiology 

1. Global Burden

  1. Acute diarrheal disease is one of the most common infectious diseases worldwide.

  2. It is a leading cause of morbidity and mortality in children under 5 years of age.

  3. Developing countries bear the highest burden.

  4. Millions of episodes occur annually, especially in low-income regions.

  5. Mortality is mainly due to severe dehydration and electrolyte imbalance.

2. Geographic Distribution

  1. Highly prevalent in:

    • South Asia

    • Sub-Saharan Africa

    • Latin America

  2. Rural areas are more affected than urban areas.

  3. Slum populations show higher incidence due to:

    • Overcrowding

    • Poor sanitation

    • Unsafe water

3. Age Distribution

  1. Most affected group: Children below 5 years.

  2. Infants (6 months–2 years) are at highest risk.

  3. Elderly individuals are also vulnerable.

  4. Immunocompromised patients show higher severity.

4. Seasonal Variation

  1. More common during:

    • Summer season

    • Rainy season

  2. Bacterial diarrhea peaks in summer.

  3. Viral diarrhea (especially Rotavirus) is more common in winter in some regions.

  4. Monsoon increases contamination of water sources.

5. Mode of Transmission

  1. Fecal–oral route (most common).

  2. Contaminated drinking water.

  3. Contaminated food.

  4. Poor hand hygiene.

  5. Person-to-person contact (e.g., Norovirus outbreaks).

  6. Flies acting as mechanical vectors.

6. Risk Factors

  1. Lack of safe drinking water.

  2. Poor sanitation facilities.

  3. Open defecation.

  4. Malnutrition.

  5. Bottle feeding (instead of breastfeeding).

  6. Incomplete vaccination (e.g., rotavirus vaccine).

  7. Low socioeconomic status.

  8. Overcrowding.

7. Causative Organisms in Epidemiology

A. Bacterial

  1. Vibrio cholerae – Causes epidemics of cholera.

  2. Escherichia coli – Common in traveler’s diarrhea.

  3. Shigella dysenteriae – Causes bacillary dysentery.

  4. Salmonella enterica – Foodborne outbreaks.

B. Viral

  1. Rotavirus – Major cause in children.

  2. Norovirus – Outbreaks in communities.

C. Parasitic

  1. Entamoeba histolytica

  2. Giardia lamblia

8. Outbreak Epidemiology

  1. Occurs due to:

    • Contaminated water supply

    • Contaminated food

    • Natural disasters (floods)

  2. Rapid spread in:

    • Schools

    • Hostels

    • Military camps

    • Refugee camps

  3. Cholera outbreaks can affect thousands rapidly.

  4. Prompt laboratory confirmation is essential for outbreak control.

9. Socioeconomic Impact

  1. Increased hospital admissions.

  2. Loss of school days in children.

  3. Loss of productivity in adults.

  4. Increased healthcare costs.

  5. Nutritional deterioration in children.

10. Preventive Epidemiological Measures

  1. Safe water supply.

  2. Sanitation improvement programs.

  3. Health education.

  4. Breastfeeding promotion.

  5. Vaccination (Rotavirus vaccine).

 

Etiology

Acute diarrhea may be caused by infectious and non-infectious agents.

A. Infectious Causes

1. Bacterial Causes

  1. Vibrio cholerae

    • Causes cholera

    • Severe watery diarrhea

    • Epidemic outbreaks

  2. Escherichia coli

    • ETEC → Traveler’s diarrhea

    • EHEC → Bloody diarrhea

    • EPEC → Infantile diarrhea

  3. Shigella dysenteriae

    • Bacillary dysentery

    • Blood and mucus in stool

  4. Salmonella enterica

    • Food-borne gastroenteritis

    • Fever with diarrhea

  5. Clostridium perfringens

    • Food poisoning

    • Abdominal cramps

2. Viral Causes

  1. Rotavirus

    • Most common in children

    • Severe watery diarrhea

  2. Norovirus

    • Outbreaks in closed communities

  3. Adenovirus (enteric type)

3. Parasitic Causes

  1. Entamoeba histolytica

    • Amoebic dysentery

  2. Giardia lamblia

    • Malabsorption diarrhea

  3. Cryptosporidium

B. Non-Infectious Causes

  1. Food intolerance

  2. Drug-induced diarrhea (antibiotics)

  3. Toxins

  4. Malabsorption syndromes

 

Pathogenesis

The mechanism of diarrhoea depends on the causative agent.

A. Secretory Diarrhea

  1. Caused by enterotoxin production.

  2. Example: Vibrio cholerae

  3. Mechanism:

    • Cholera toxin activates adenylate cyclase.

    • Increased cAMP in intestinal cells.

    • Increased chloride and water secretion.

    • Massive watery diarrhea.

  4. Stool contains:

    • Large volume

    • No blood

  5. Continues even during fasting.

B. Inflammatory (Invasive) Diarrhea

  1. Caused by mucosal invasion.

  2. Example:

    • Shigella dysenteriae

    • EHEC (E. coli)

  3. Mechanism:

    • Invasion of intestinal epithelium.

    • Ulcer formation.

    • Inflammation.

  4. Stool contains:

    • Blood

    • Mucus

    • Pus cells

  5. Associated with fever.

C. Osmotic Diarrhea

  1. Caused by malabsorption.

  2. Undigested solutes retain water in intestine.

  3. Stops during fasting.

  4. Example:

    • Giardia infection.

D. Motility-Related Diarrhea

  1. Increased intestinal motility.

  2. Reduced contact time for absorption.

  3. Seen in:

    • Irritable bowel syndrome.

 

Clinical Feature

Clinical features vary depending on severity and cause.

A. General Symptoms

  1. Passage of loose or watery stools (≥3 per day).

  2. Abdominal cramps.

  3. Nausea.

  4. Vomiting.

  5. Fever (in invasive diarrhea).

  6. Weakness.

B. Stool Characteristics

Type Features
Watery Secretory diarrhea (e.g., cholera)
Bloody Dysentery (Shigella, EHEC)
Mucoid Inflammatory
Foul-smelling Parasitic

C. Signs of Dehydration

  1. Dry mouth and tongue.

  2. Sunken eyes.

  3. Decreased skin turgor.

  4. Tachycardia.

  5. Hypotension.

  6. Reduced urine output.

  7. Lethargy.

D. Severity Classification

1. Mild

  • No dehydration.

  • Normal pulse and blood pressure.

2. Moderate

  • Thirsty.

  • Dry mucosa.

  • Slight tachycardia.

3. Severe

  • Shock.

  • Very low BP.

  • Cold extremities.

  • Altered consciousness.

E. Complications

  1. Severe dehydration.

  2. Electrolyte imbalance.

  3. Hypokalemia.

  4. Metabolic acidosis.

  5. Renal failure.

  6. Hemolytic uremic syndrome (EHEC).

  7. Septicemia (Salmonella).

 

Laboratory Diagnosis

Specimen Collection

A. Types of Specimens

  1. Fresh stool sample (preferred).

  2. Rectal swab (if stool not available).

  3. Suspected food sample (during outbreaks).

  4. Blood sample (if systemic infection suspected).

B. Collection Guidelines

  1. Collect before starting antibiotics.

  2. Use sterile, wide-mouthed, leak-proof container.

  3. Avoid contamination with urine.

  4. Send to lab immediately.

  5. If delay >2 hours → use Cary-Blair transport medium.

Macroscopic Examination of Stool

  1. Color

    • Yellow/brown → Normal

    • Pale → Malabsorption

    • Red → Blood

    • Greenish → Infection

  2. Consistency

    • Watery → Secretory diarrhea

    • Mucoid → Inflammatory

    • Bloody → Dysentery

  3. Odor

    • Foul smell → Parasitic infection

  4. Presence of:

    • Blood

    • Mucus

    • Worms

Microscopic Examination

A. Wet Mount Preparation

  1. Normal saline mount → Motility detection.

  2. Iodine mount → Cyst identification.

Detects:

  • Ova

  • Cysts

  • Trophozoites

  • RBC

  • WBC

B. Interpretation

  1. RBC present → Suggests invasive diarrhea

    • Example: Shigella dysenteriae

  2. WBC present → Inflammatory diarrhea

  3. No RBC/WBC → Secretory diarrhea

    • Example: Vibrio cholerae

  4. Ova/Cysts present → Parasitic infection

    • Entamoeba histolytica

    • Giardia lamblia

Stool Culture

A. Indications

  1. Severe diarrhea.

  2. Bloody diarrhea.

  3. High fever.

  4. Suspected outbreak.

  5. Immunocompromised patient.

B. Culture Media Used

Organism Media
Escherichia coli MacConkey agar
Salmonella enterica XLD agar
Shigella dysenteriae SS agar
Vibrio cholerae TCBS agar

C. Colony Characteristics

  1. Lactose fermenters → Pink colonies (MacConkey).

  2. Non-lactose fermenters → Colorless colonies.

  3. Yellow colonies on TCBS → Vibrio cholerae.

  4. Black-centered colonies on XLD → Salmonella (H₂S production).

Biochemical Tests

  1. TSI (Triple Sugar Iron test).

  2. Indole test.

  3. Citrate test.

  4. Urease test.

  5. Oxidase test (Vibrio positive).

  6. Coagulase (for Staphylococcus in food poisoning).

Serological Tests

  1. Widal test → Salmonella.

  2. Rapid antigen test → Rotavirus.

  3. ELISA → Viral antigens.

Molecular Diagnosis

  1. PCR → Detect bacterial toxin genes.

  2. Multiplex PCR panels → Detect multiple pathogens.

  3. Real-time PCR → Rapid diagnosis.

Advantages:

  • High sensitivity.

  • Rapid results.

Antibiotic Sensitivity Testing (AST)

  1. Performed after bacterial isolation.

  2. Kirby-Bauer disk diffusion method.

  3. Guides appropriate antibiotic therapy.

  4. Important in resistant infections.

Special Investigations

  1. Electrolyte estimation (Na⁺, K⁺).

  2. Blood urea and creatinine (renal function).

  3. ABG (metabolic acidosis).

  4. Complete blood count (CBC).

Interpretation of Laboratory Findings

Finding Suggests
Watery stool, no WBC Secretory diarrhea
RBC + WBC Invasive diarrhea
Ova/Cyst Parasitic infection
Positive culture Bacterial cause

 

Treatment

Rehydration Therapy 

A. Oral Rehydration Therapy (ORT)

  1. First-line treatment in most cases.

  2. Prevents dehydration-related mortality.

  3. Can be given at home.

Composition of WHO ORS (Low Osmolarity)

  1. Sodium chloride

  2. Glucose

  3. Potassium chloride

  4. Trisodium citrate

Mechanism

  1. Glucose enhances sodium absorption.

  2. Sodium absorption promotes water absorption.

  3. Corrects dehydration and electrolyte imbalance.

B. Indications for ORS

  1. Mild dehydration.

  2. Moderate dehydration.

  3. Continued diarrhea after IV therapy.

Intravenous (IV) Fluid Therapy

Indications

  1. Severe dehydration.

  2. Shock.

  3. Persistent vomiting.

  4. Unable to drink orally.

Fluids Used

  1. Ringer lactate (preferred).

  2. Normal saline.

Monitoring

  1. Pulse rate.

  2. Blood pressure.

  3. Urine output.

  4. Electrolytes.

Zinc Supplementation (Especially in Children)

  1. Recommended in children under 5 years.

  2. Dose:

    • 10 mg/day (<6 months)

    • 20 mg/day (>6 months)

  3. Duration: 14 days.

  4. Benefits:

    • Reduces duration of diarrhea.

    • Reduces recurrence.

Antibiotic Therapy

Indications

  1. Cholera

    • Vibrio cholerae

  2. Bacillary dysentery

    • Shigella dysenteriae

  3. Severe Salmonella infection

    • Salmonella enterica

  4. Immunocompromised patients.

Not Indicated In

  1. Viral diarrhea (e.g., Rotavirus).

  2. Mild watery diarrhea.

Important Note

  • Overuse leads to antibiotic resistance.

  • Antibiotics must be based on culture and sensitivity report.

Anti-diarrheal Drugs

  1. Generally NOT recommended in children.

  2. Avoid in dysentery (bloody diarrhea).

  3. May prolong infection.

Nutritional Management

  1. Continue breastfeeding.

  2. Do not stop feeding.

  3. Give light, easily digestible diet.

  4. Avoid fatty and spicy food.

  5. Prevent malnutrition.

Management of Complications

  1. Severe dehydration → IV fluids.

  2. Hypokalemia → Potassium correction.

  3. Metabolic acidosis → Correct fluids.

  4. Shock → Emergency management.

 

Prevention

1. Primary Prevention

A. Safe Water Supply

  1. Boiled water.

  2. Chlorinated water.

  3. Proper water storage.

B. Sanitation

  1. Proper sewage disposal.

  2. Use of toilets.

  3. Avoid open defecation.

C. Hand Hygiene

  1. Wash hands before eating.

  2. Wash hands after toilet use.

  3. Use soap and clean water.

D. Food Hygiene

  1. Cook food properly.

  2. Avoid stale food.

  3. Cover food to prevent flies.

  4. Wash fruits and vegetables properly.

2. Immunization

  1. Rotavirus vaccine for infants.

  2. Cholera vaccine in endemic areas.

Vaccination reduces:

  • Severity

  • Hospitalization

  • Mortality

3. Breastfeeding Promotion

  1. Exclusive breastfeeding for 6 months.

  2. Protects against infections.

  3. Provides immunity.

4. Health Education

  1. Community awareness programs.

  2. School health programs.

  3. Teaching ORS preparation at home.

5. Surveillance & Outbreak Control

  1. Early reporting of cases.

  2. Laboratory confirmation.

  3. Isolation during outbreaks.

  4. Disinfection of contaminated sources.

 

MCQs

1. Acute diarrhea is defined as diarrhea lasting less than:

A. 7 days
B. 10 days
C. 14 days
D. 30 days
Answer: C

2. The most common cause of acute diarrhea in children is:

A. Rotavirus
B. Salmonella
C. Giardia
D. Shigella
Answer: A

3. The major cause of death in acute diarrhea is:

A. Fever
B. Vomiting
C. Dehydration
D. Abdominal pain
Answer: C

4. Rice-water stool is characteristic of:

A. Shigella
B. Vibrio cholerae
C. Salmonella
D. E. coli
Answer: B

5. Bloody diarrhea is most commonly caused by:

A. Rotavirus
B. Norovirus
C. Shigella dysenteriae
D. Vibrio
Answer: C

6. The most important treatment in ADD is:

A. Antibiotics
B. ORS
C. Steroids
D. Antacids
Answer: B

7. ORS works by enhancing absorption of:

A. Protein
B. Fat
C. Sodium and water
D. Iron
Answer: C

8. Severe dehydration requires:

A. ORS only
B. IV fluids
C. Antibiotics only
D. Zinc only
Answer: B

9. TCBS agar is used to isolate:

A. Salmonella
B. Vibrio cholerae
C. Shigella
D. E. coli
Answer: B

10. RBC in stool suggests:

A. Secretory diarrhea
B. Viral infection
C. Invasive diarrhea
D. Osmotic diarrhea
Answer: C

11. The most common mode of transmission is:

A. Airborne
B. Vector-borne
C. Fecal-oral route
D. Blood transfusion
Answer: C

12. Zinc supplementation is recommended for:

A. Adults
B. Children
C. Elderly only
D. Pregnant women
Answer: B

13. Lactose fermenting colonies on MacConkey agar appear:

A. Colorless
B. Pink
C. Black
D. Green
Answer: B

14. Non-lactose fermenter:

A. Salmonella enterica
B. E. coli
C. Klebsiella
D. Enterobacter
Answer: A

15. Secretory diarrhea continues during:

A. Feeding
B. Fasting
C. Exercise
D. Sleep
Answer: B

16. The toxin of Vibrio cholerae increases:

A. cAMP
B. cGMP
C. ATP
D. DNA
Answer: A

17. Most rapid diagnostic method:

A. Culture
B. Microscopy
C. PCR
D. Wet mount
Answer: C

18. Ova and cyst in stool indicate:

A. Viral infection
B. Bacterial infection
C. Parasitic infection
D. Chemical poisoning
Answer: C

19. Hypokalemia is a complication of:

A. Mild diarrhea
B. Severe diarrhea
C. Constipation
D. IBS
Answer: B

20. Transport medium for stool:

A. Nutrient broth
B. Cary-Blair medium
C. Blood agar
D. TCBS
Answer: B

21. Most common viral outbreak agent:

A. Norovirus
B. Rotavirus
C. Influenza
D. Adenovirus
Answer: A

22. Black-centered colonies on XLD suggest:

A. E. coli
B. Vibrio
C. Salmonella
D. Shigella
Answer: C

23. Decreased skin turgor indicates:

A. Fever
B. Dehydration
C. Hypertension
D. Anemia
Answer: B

24. ORS should be prepared with:

A. Hot milk
B. Juice
C. Clean water
D. Tea
Answer: C

25. Most common age group affected:

A. Adults
B. Elderly
C. Under 5 years
D. Teenagers
Answer: C

26. Fever with diarrhea suggests:

A. Viral infection
B. Invasive bacterial infection
C. Chemical poisoning
D. Osmotic diarrhea
Answer: B

27. Indole positive organism:

A. Escherichia coli
B. Salmonella
C. Shigella
D. Vibrio
Answer: A

28. Severe dehydration may lead to:

A. Hypertension
B. Shock
C. Diabetes
D. Asthma
Answer: B

29. Most important preventive measure:

A. Steroids
B. Vaccination only
C. Hand washing
D. Surgery
Answer: C

30. Rotavirus mainly affects:

A. Adults
B. Children
C. Elderly
D. Pregnant women
Answer: B

31. Blood and mucus in stool is typical of:

A. Cholera
B. Dysentery
C. Viral diarrhea
D. Osmotic diarrhea
Answer: B

32. Cholera outbreaks are common after:

A. Earthquake
B. Flood
C. Winter
D. Drought
Answer: B

33. Hypotension in ADD indicates:

A. Mild disease
B. Severe dehydration
C. Recovery
D. Constipation
Answer: B

34. MacConkey agar differentiates bacteria based on:

A. Hemolysis
B. Lactose fermentation
C. Motility
D. Spore formation
Answer: B

35. Antibiotics are NOT required in:

A. Cholera
B. Dysentery
C. Rotavirus infection
D. Severe Salmonella
Answer: C

36. Most common complication in children:

A. Malnutrition
B. Cancer
C. Hypertension
D. Arthritis
Answer: A

37. WBC in stool indicates:

A. Secretory diarrhea
B. Inflammatory diarrhea
C. Viral infection
D. Osmotic diarrhea
Answer: B

38. Major electrolyte lost in diarrhea:

A. Iron
B. Calcium
C. Sodium
D. Iodine
Answer: C

39. Best initial management in mild ADD:

A. Antibiotics
B. ORS
C. IV fluids
D. Surgery
Answer: B

40. Stool culture is indicated in:

A. Mild watery diarrhea
B. Bloody diarrhea
C. IBS
D. Constipation
Answer: B

41. Hypovolemic shock results from:

A. Fever
B. Dehydration
C. Vomiting only
D. Hypertension
Answer: B

42. Exclusive breastfeeding protects against:

A. Hypertension
B. Diarrhea
C. Diabetes
D. Cancer
Answer: B

43. Motility-related diarrhea occurs due to:

A. Increased intestinal movement
B. Toxin
C. Infection
D. Ulcer
Answer: A

44. EHEC may cause:

A. Cholera
B. Hemolytic uremic syndrome
C. Tuberculosis
D. Hepatitis
Answer: B

45. The gold standard for bacterial identification:

A. Microscopy
B. Culture
C. PCR
D. Serology
Answer: B

46. Shock in ADD requires:

A. ORS only
B. Immediate IV fluids
C. Zinc
D. Antacids
Answer: B

47. Most common transmission in children:

A. Blood
B. Fecal-oral
C. Air
D. Vector
Answer: B

48. Secretory diarrhea is characterized by:

A. Blood in stool
B. Large watery stool
C. Severe pain
D. Ulcer
Answer: B

49. Dysentery is defined by:

A. Watery stool
B. Loose stool only
C. Blood and mucus in stool
D. Constipation
Answer: C

50. The cornerstone of management of ADD is:

A. Steroids
B. ORS
C. Antibiotics
D. Surgery
Answer: B

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