In the foodborne outbreak investigation, which food had the highest attack rate?

• A. Chicken sandwich
• B. Spinach
• C. Egg salad
• D. Cantaloupe

Answer: (B)

Attack rate is the proportion of people who became ill among those who were exposed to a particular food. In outbreak investigations, comparing attack rates across foods helps identify the vehicle most strongly associated with illness. The food with the highest attack rate indicates the strongest link between exposure and illness, pointing to it as the likely source.

Spinach having the highest attack rate means that among those who ate spinach, a larger share fell ill compared with all other foods. This strong exposure–illness link makes spinach the most probable vehicle of transmission in this outbreak. The other foods may have been consumed by more people or resulted in fewer illnesses among those exposed, leading to lower attack rates even if some illnesses occurred with those foods.