To identify transient triggers of acute myocardial infarction, researchers enrol patients immediately after an MI and ask them about heavy physical exertion in the 2 hours before symptom onset compared with the same 2-hour window on the previous day, serving as their own control. Which design is this?

• A Nested case-control study
• B Case-crossover study ✓
• C Retrospective cohort study
• D Cross-over randomized trial

Explanation

The case-crossover design compares each case's exposure in a hazard period just before the event with exposure in a defined control period for the same individual, making each patient his own control. It suits brief, intermittent exposures with immediate effects such as exertion, anger, or air pollution spikes preceding an MI. A cross-over trial involves deliberate randomization to treatment sequences, and a retrospective cohort starts with exposure status, neither of which applies here.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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