In the epidemiological investigation of a foodborne outbreak in a school, the attack rate for those who ate the salad was 75% (60/80) and for those who did NOT eat the salad was 15% (6/40). The Relative Risk of illness from eating salad is:
- A 3.0
- B 5.0 ✓
- C 4.0
- D 6.0
Correct answer: B. 5.0
Explanation
RR = Attack rate in exposed / Attack rate in unexposed = 0.75 / 0.15 = 5.0. Those who ate the salad had 5 times the risk of illness compared to those who did not. This high RR strongly implicates the salad as the vehicle of transmission. In outbreak investigations, RR (or OR in case-control outbreak investigations) is calculated for each food item in a food-specific attack rate table. The food with the highest RR and statistical significance is the implicated vehicle. Chi-square or Fisher's test confirms statistical significance.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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