Question: A flu outbreak occurred in a small college dormitory that housed 20 students. Case A began on October 1 and case B was diagnosed on October 2. After approximately 10 days, 12 additional cases occurred during approximately a one-week time span. University epidemiologists believed that this second group of cases represented the same generation of cases, and was in the second incubation period after the occurrences of cases A and B; none of the 20 students was known to be immune. Calculate and interpret the secondary attack rate.