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Outbreak attack rate — USMLE Step 3 MCQ

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ModeratePreventive Medicine, Epidemiology, BiostatisticsOutbreak attack rateUSMLE Step 3

At a wedding, 60 of 120 guests who ate chicken salad develop vomiting and diarrhea within 8 hours. Among 80 guests who did not eat chicken salad, 4 become ill. Investigators want the food-specific attack rate among exposed guests. Which of the following is the most appropriate at this time?

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Correct answer: E — 50%

Food-specific attack rate among exposed guests is ill exposed divided by total exposed: 60/120 = 50%.

Reference: CDC Outbreak Investigation Principles