Following a wedding feast, an outbreak investigation finds that 40 of 100 persons who ate chicken salad developed gastroenteritis, compared with 20 of 200 persons who did not eat it. What is the relative risk of illness associated with eating the chicken salad?
- A 0.25
- B 2.0
- C 4.0 ✓
- D 30%
Correct answer: C. 4.0
Explanation
Attack rate among the exposed is 40/100 = 40%. Attack rate among the unexposed is 20/200 = 10%. Relative risk = 40/10 = 4. Option D (30%) is the attributable risk (difference between the two attack rates), not the ratio, and this is the single most common trap in outbreak relative risk questions.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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