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Difficulty: EasyStudy Design

A public health department is investigating an outbreak of a novel respiratory pathogen among workers at a large agricultural facility. To identify potential risk factors, health officials select 45 workers who have confirmed infections and 135 workers from the same facility who have tested negative. Detailed occupational histories are then obtained from all participants to determine their specific duties, locations within the facility, and use of personal protective equipment over the preceding three weeks. Which of the following best describes this epidemiological study design?

  1. Case-control studyAnswer
  2. B
    Retrospective cohort study
  3. C
    Cross-sectional study
  4. D
    Prospective cohort study
  5. E
    Randomized controlled trial

Answer

Case-control study
The correct answer is a case-control study because the participants were initially identified and grouped based on their outcome or disease status (infected versus uninfected). After these groups were formed, the investigators looked backward in time to assess their prior exposures, such as specific occupational duties and protective equipment use. This retrospective assessment of exposure based on a known disease status is the defining characteristic of a case-control design, making it highly efficient for investigating outbreaks or rare diseases.

Step-by-Step Solution

1
Determine how the study groups were initially selected.
Participants were selected based on whether they had the respiratory infection (cases) or did not have the infection (controls).
The defining feature of a study design is often how the initial population is stratified.
2
Identify the temporal direction of the data collection regarding exposure.
The investigators gathered detailed occupational histories from the preceding three weeks, meaning they looked backward in time to assess past exposures.
Understanding the timeline (prospective vs. retrospective) distinguishes between different observational designs.
3
Synthesize the group selection method and the temporal direction to classify the study.
A study that selects participants based on outcome status (disease vs. no disease) and investigates past exposure status is a case-control study.
This directly matches the definition of a case-control design.

Key Concept

Observational study designs are primarily categorized by how participants are selected (by exposure or by outcome) and the temporal direction of the investigation.
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Topics

Study Design

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