Outbreak Management for MCCQE1

Introduction

Outbreak management is a critical competency within the Public Health and Population Health domains of the MCCQE1. As a future Canadian physician, you are expected to embody the CanMEDS roles of Medical Expert (diagnosing and treating) and Health Advocate (protecting community health).

Understanding how to investigate and control an outbreak is not just for public health officers; clinicians are often the “first receivers” who identify the signal amidst the noise. This guide provides a structured approach to outbreak management, tailored for MCCQE1 preparation.

Core Definitions

Before diving into the steps of investigation, clarify these epidemiological terms essential for the MCCQE1.

10 Steps of Outbreak Investigation

The MCCQE1 often tests the sequence of these steps. While in practice steps may occur simultaneously, for exam purposes, knowing the logical order is crucial.

Analytical Epidemiology: Cohort vs. Case-Control

For MCCQE1, you must choose the correct study design and calculate the appropriate measure of association.

RR = (Incidence in Exposed) / (Incidence in Unexposed)

OR = (Odds of exposure in cases) / (Odds of exposure in controls)
OR = (ad) / (bc)

Epidemic Curves

Interpreting an “Epi Curve” is a high-yield skill for the MCCQE1.

1. Point Source:

   • Sharp rise and fall.
   • Cases occur within one incubation period.
   • Example: Staphylococcal food poisoning at a picnic.

2. Continuous Common Source:

   • Rise to a plateau and stays elevated.
   • Exposure is ongoing.
   • Example: Contaminated municipal water supply (Walkerton, Ontario).

3. Propagated (Person-to-Person):

   • Progressively taller peaks.
   • Peaks are separated by the incubation period of the disease.
   • Example: Measles or Influenza spread.

Canadian Guidelines and Legal Framework

Public Health Agency of Canada (PHAC)

PHAC is the federal agency responsible for public health, emergency preparedness, and response. However, healthcare delivery and direct outbreak management are primarily provincial/territorial responsibilities.

Reportable Diseases

In Canada, physicians have a legal duty to report specific communicable diseases to the local Medical Officer of Health (MOH).

• Federal: Quarantine Act (for international borders).
• Provincial: Public Health Acts (e.g., Health Protection and Promotion Act in Ontario).

Key Canadian Guidelines (Examples)

• Norovirus in Healthcare Facilities: Strict contact precautions, cohorting of staff/patients, and enhanced environmental cleaning (bleach). Alcohol-based hand rub is less effective against Norovirus; soap and water are preferred.
• Influenza in Long-Term Care: If an outbreak is declared (definition varies, typically 2+ cases within 48h), chemoprophylaxis (Oseltamivir) is often recommended for all non-ill residents regardless of vaccination status.

Key Points to Remember for MCCQE1

• Attack Rate Calculation: $\text{Attack Rate} = \frac{\text{Number of new cases}}{\text{Number of people at risk}} \times 100$
• Food Poisoning Timelines:
  • < 6 hours: Staph aureus or Bacillus cereus (preformed toxin).
  • 12-24 hours: C. perfringens.
  • 24-48 hours: Norovirus.
  • Days: Salmonella, Campylobacter, E. coli.
• Priority: In a suspected outbreak, protecting public health (Step 8: Control Measures) often begins before the investigation is complete, especially if the source is obvious or the risk is high. However, if asked for the first step, it is usually to confirm/verify the outbreak.

Sample Question

Clinical Scenario

A 34-year-old family physician in rural Saskatchewan notices an unusual number of patients presenting with bloody diarrhea and severe abdominal cramps over a 48-hour period. Most patients report attending a local fall fair three days prior. One patient, an 8-year-old boy, has been hospitalized with signs of hemolytic uremic syndrome (HUS). The physician suspects an outbreak of E. coli O157:H7.

Which one of the following is the most appropriate initial step for the physician to take?

• A. Prescribe prophylactic antibiotics to all family members of the affected patients.
• B. Contact the organizers of the fall fair to shut down food vendors immediately.
• C. Report the suspected cases to the local public health authority.
• D. Conduct a case-control study to identify the specific food item responsible.
• E. Collect stool samples from all attendees of the fall fair to identify asymptomatic carriers.

Explanation

The correct answer is:

• C. Report the suspected cases to the local public health authority.

Detailed Explanation:

• C is correct: The physician’s primary legal and ethical responsibility (Health Advocate/Medical Expert) upon suspecting a reportable communicable disease outbreak is to notify the local public health authority (Medical Officer of Health). Public health authorities have the jurisdiction, resources, and legal mandate to investigate and manage outbreaks.
• A is incorrect: Antibiotics are generally contraindicated in E. coli O157:H7 infections because they may increase the release of Shiga toxin and precipitate Hemolytic Uremic Syndrome (HUS). Furthermore, prophylaxis is not the initial step.
• B is incorrect: While closing the source is a control measure, the physician does not have the legal authority to shut down vendors unilaterally. This is a function of public health inspectors/officials after an initial assessment.
• D is incorrect: Conducting a case-control study is part of the analytical epidemiology phase (Step 6) performed by public health epidemiologists, not the reporting clinician.
• E is incorrect: Testing all attendees is logistically impossible and unnecessary. Case finding focuses on symptomatic individuals first.

References

1. Public Health Agency of Canada. (n.d.). Outbreak Investigation and Management. Retrieved from Canada.ca .
2. Association of Faculties of Medicine of Canada (AFMC). (n.d.). AFMC Primer on Population Health. Chapter 11: Infectious Disease Control.
3. Medical Council of Canada. (n.d.). MCCQE Part I Objectives: Population Health.
4. Heymann, D. L. (Ed.). (2015). Control of Communicable Diseases Manual. American Public Health Association.