Study Design for Food Poisoning Outbreak Investigation
The correct answer is A - case-control study. When investigating a food poisoning outbreak after a festival by interviewing infected cases to identify the causative food, researchers are conducting a case-control study 1.
Why This is a Case-Control Study
Case-control studies compare patients ('cases') with unaffected individuals ('controls') to identify exposures that may have caused the disease. 1 This design is specifically suited for outbreak investigations because:
- Cases are identified first (people who became ill after the festival), then compared to controls (attendees who did not become ill) 1
- The study looks backward from disease to exposure, examining what foods were consumed by cases versus controls 1
- It is quick, efficient, and resource-effective for investigating acute outbreaks where rapid identification of the source is critical 1
Real-World Application in Outbreak Investigations
The Connecticut Salmonella outbreak investigation exemplifies this approach perfectly: investigators identified 9 case-patients and 14 control subjects among reception attendees, then compared food exposures between groups, finding that potato salad consumption was strongly associated with illness (OR = 84.0) 1.
Case-control studies are the standard epidemiological method for foodborne outbreak investigations because they allow rapid hypothesis testing when time is critical 1, 2, 3. In the Philippine village festival outbreak, investigators used a case-control study with 64 cases and 123 controls to identify Filipino-style beef stew (OR: 6.62) and stir-fried noodles (OR: 3.15) as risk factors 2.
Why Not the Other Options
Cohort studies (Option B) follow a population forward in time from exposure to outcome, requiring substantial effort, resources, and time 1. This design is impractical for acute outbreak investigations where the exposure has already occurred 1
Randomized controlled trials (Option C) involve random allocation of participants to intervention or control groups 1. This is neither ethical nor feasible for investigating disease outbreaks, as you cannot randomly assign people to consume potentially contaminated food 1
Key Methodological Points
The case-control design is particularly valuable when evaluating populations with rare events or when rapid investigation is needed 1. Among 251 foodborne outbreaks investigated in France, 62 (25%) used case-control studies, with 74% successfully identifying the responsible food with confirmation, compared to only 17% success in surveys without case-control methodology 3.
Common pitfalls to avoid in outbreak case-control studies include: