Acute Diarrhea: MCCQE1 Preparation Guide

Introduction

Acute diarrhea is a common presentation in Canadian primary care and emergency departments. For MCCQE1 preparation, it is crucial to distinguish between self-limiting viral gastroenteritis and serious pathologies requiring intervention.

Definition: Acute diarrhea is defined as the passage of loose or watery stools (typically $\ge$3 times in a 24-hour period) lasting less than 14 days.

Symptoms lasting 14–30 days are termed persistent diarrhea, and those lasting >30 days are chronic diarrhea.

Etiology and Pathophysiology

Understanding the underlying cause is essential for the Medical Expert role. In Canada, viral etiology is the most common cause of acute diarrhea in both adults and children.

Pathophysiological Mechanisms

1. Secretory: Active secretion of ions (e.g., Cholera, ETEC). Large volume, watery, persists with fasting.
2. Osmotic: Malabsorption of solutes (e.g., Lactose intolerance, osmotic laxatives). Stops with fasting.
3. Inflammatory (Exudative): Mucosal damage (e.g., Shigella, IBD). Blood/pus in stool, fever.
4. Motility-related: Hyperthyroidism, IBS.

Clinical Evaluation

History Taking

For the MCCQE1, focus on risk stratification and identifying red flags.

Physical Examination

The priority is assessing volume status.

Dehydration Assessment Table

Crucial for MCCQE1 Pediatrics and Internal Medicine

Investigations

When to Investigate?

Perform investigations only if “Red Flags” are present or if the results will change management/public health response.

1. Stool Culture & Sensitivity:

   • Bloody diarrhea (dysentery).
   • Severe dehydration or sepsis.
   • Symptoms >7 days.
   • Immunocompromised host.
   • Public health concern (food handler, healthcare worker, daycare).

2. Ova & Parasites (O&P):

   • Persistent diarrhea (>14 days).
   • History of travel to endemic areas.
   • Exposure to untreated water (Canadian wilderness - Giardia).

3. Clostridioides difficile Toxin:

   • Recent hospitalization or antibiotic use (within 3 months).
   • Unexplained leukocytosis in hospitalized patients.

4. Blood Work (CBC, Electrolytes, Creatinine):

   • Indicated only in severe dehydration, sepsis, or need for IV fluids.

Management

Management focuses on supportive care. The MCCQE1 tests your ability to prioritize rehydration over pharmacological interventions.

Canadian Guidelines & Public Health

Reportable Diseases

In Canada, certain pathogens are nationally reportable to the Public Health Agency of Canada (PHAC). Physicians must report confirmed cases to local public health units.

• Salmonella
• Shigella
• Campylobacter
• Verotoxigenic E. coli (e.g., O157:H7)
• Giardiasis

E. coli O157:H7 and HUS

C. difficile Management (Canadian Context)

Recent guidelines have shifted.

• First Episode (Non-severe & Severe): Oral Vancomycin 125 mg QID x 10 days OR Fidaxomicin 200 mg BID x 10 days.
• Fulminant (Hypotension/Ileus): Oral Vancomycin (high dose) + IV Metronidazole + Vancomycin PR (rectal).

Key Points to Remember for MCCQE1

Use this checklist for your final review:

• Most common cause: Viral (Norovirus/Rotavirus).
• Most common bacterial cause in Canada: Campylobacter jejuni.
• “Beaver Fever”: Giardia lamblia (Hikers/Campers/Untreated water).
• Pediatric Rehydration: ORT is superior to IV for mild/moderate dehydration.
• Contraindication: Do not give anti-motility drugs (Loperamide) in bloody diarrhea or fever.
• Hemolytic Uremic Syndrome: Triad of Microangiopathic Hemolytic Anemia + Thrombocytopenia + Acute Kidney Injury. Associated with E. coli O157:H7.
• Choosing Wisely: Don’t culture everyone.

Sample Question

Clinical Scenario

A 28-year-old male presents to his family physician with a 2-day history of loose, watery stools occurring 4–5 times per day. He reports mild abdominal cramping but denies fever, blood in the stool, or vomiting. He returned 3 days ago from an all-inclusive resort in Mexico. His vital signs are: BP 120/75 mmHg, HR 78 bpm, Temp 37.1°C. The physical examination reveals a soft, non-tender abdomen and moist mucous membranes.

Question

Which one of the following is the most appropriate initial management for this patient?

Options

• A. Prescribe ciprofloxacin 500 mg orally twice daily for 3 days
• B. Order stool culture and sensitivity and ova and parasite testing
• C. Prescribe loperamide 4 mg initially, then 2 mg after each loose stool
• D. Prescribe azithromycin 1000 mg orally as a single dose
• E. Refer to the emergency department for intravenous fluid hydration

Explanation

The correct answer is:

• C. Prescribe loperamide 4 mg initially, then 2 mg after each loose stool

• Diagnosis: The patient has acute traveler’s diarrhea, likely non-dysenteric (no blood, no fever). The most common etiology is Enterotoxigenic E. coli (ETEC).
• Option C (Correct): For mild-to-moderate traveler’s diarrhea without dysentery (fever or blood), symptomatic management with anti-motility agents like loperamide is safe and effective. It reduces the duration of diarrhea and allows the patient to resume normal activities. Hydration should also be encouraged, but loperamide is the specific management intervention listed that is appropriate.
• Option A & D (Incorrect): Antibiotics (Ciprofloxacin or Azithromycin) are generally reserved for moderate-to-severe cases or those with dysentery (bloody stools, fever). While they can shorten the duration of illness, stewardship principles discourage their use in mild, non-dysenteric cases to prevent resistance and side effects.
• Option B (Incorrect): Stool investigations are not indicated for acute, non-severe diarrhea lasting less than 7 days unless there are red flags (fever, blood, immunocompromised state).
• Option E (Incorrect): This patient has stable vitals and moist mucous membranes, indicating no significant dehydration. Oral hydration is sufficient; IV fluids are unnecessary and a misuse of resources.

References

1. Public Health Agency of Canada. (2023). Notifiable Diseases Online.
2. Canadian Paediatric Society. (2021). Oral rehydration therapy and early refeeding in the management of childhood gastroenteritis.
3. Choosing Wisely Canada. (2023). Gastroenterology: Five Things Physicians and Patients Should Question.
4. Medical Council of Canada. (2023). MCCQE Part I Clinical Decision Making Objectives: Diarrhea.
5. Association of Medical Microbiology and Infectious Disease Canada (AMMI). (2022). Clostridioides difficile Infection Guidelines.