Answer (a) — incorrect: Incubation period is not a particular number of days but rather a range of days, reflecting differences in the intensity of exposures and/or differing immune responses among the exposed.

Answer (b) — incorrect: This is not the correct time interval between exposure to an infectious agent and onset of disease in our outbreak.

Answer (c) — correct: Persons were first exposed to SARS on August 1 at the Amoy Apartment Complex luau party. The first cases appeared 3 days later. Thus, the incubation period for the outbreak in the Amoy Apartment Complex is from 2 to 12 days. As we know from the data collected during the outbreak investigation, the first exposure at Star Hospital occurred on August 3, with the admission of an elderly patient from the Amoy Apartment Complex who then infected attending staff members. Based on the data plots presented above, the incubation period of SARS in Star Hospital ranged from 7 to 20 days. Therefore, the correct incubation period for the entire outbreak in Epiville is from 2 to 20 days.