During a cholera outbreak investigation, the attack rate in a community consuming water from Source A is 12% and from Source B is 3%. The relative risk (RR) of cholera associated with Source A versus Source B is:
- A 4.0 ✓
- B 0.25
- C 9.0
- D 1.4
Correct answer: A. 4.0
Explanation
Relative risk = Incidence (attack rate) in exposed / Incidence in unexposed = 12% / 3% = 4.0. This means the risk of cholera is 4 times higher in consumers of Source A compared to Source B. In outbreak investigations, attack rates serve as incidence proxies in cohort (attack rate) studies. RR > 1 indicates positive association; RR = 1 is null; RR = 0.25 (option B) would be the inverse (1/4), which represents RR for Source B vs Source A.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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