Study Design for Food Poisoning Outbreak Investigation
The correct answer is B - Case-Control Study, which compares infected individuals (cases) to non-infected individuals (controls) from the same exposed population to identify which specific food items are associated with illness. 1
Rationale for Case-Control Design
A case-control study is the standard epidemiologic approach for investigating foodborne outbreaks because it systematically compares exposures between those who became ill and those who remained well after attending the same event. 1 This design allows investigators to:
- Calculate odds ratios for each food item consumed, quantifying the strength of association between specific exposures and illness 1
- Identify the contaminated food vehicle efficiently, with studies showing 74% success rates in identifying responsible foods with epidemiologic or bacteriological confirmation 2
- Generate statistical evidence even with relatively small sample sizes, as demonstrated by outbreak investigations finding odds ratios as high as 84.0 for implicated foods 1
Why Other Options Are Incorrect
Cross-sectional studies (Option A) are inappropriate for outbreak investigations because they assess health status at a single point in time without comparing exposures between cases and controls, making it impossible to identify which specific food caused the outbreak. 3
Cohort studies (Option C) are impractical for acute outbreak investigations because they require following exposed individuals forward in time to observe who develops disease, which is resource-intensive and provides delayed results when rapid identification of the contaminated food is critical. 1
Randomized controlled trials (Option D) are ethically impossible and methodologically inappropriate for investigating outbreaks, as you cannot randomly assign people to eat potentially contaminated food. 1
Implementation Approach
The investigation should proceed as follows:
- Define cases using clinical criteria (e.g., acute gastroenteritis with specific symptom onset timing after the festival) 1
- Select controls from the same population who attended the festival but remained well 1, 4
- Conduct structured interviews about all specific food items consumed at the festival 1
- Calculate odds ratios for each food exposure to identify statistical associations 1, 4
- Collect laboratory specimens from at least 10 ill persons during the first 48 hours when diagnostic yield is highest 1
Evidence Quality
Multiple outbreak investigations demonstrate the effectiveness of case-control methodology, with one study showing that among 62 foodborne outbreak investigations using case-control design, 61% successfully identified the responsible food, and an additional 16% generated strong hypotheses despite small sample sizes. 2 More recent applications have shown odds ratios of 7.67 to 12.0 for implicated foods, providing robust statistical evidence. 4, 5