Question

An influenza outbreak occurred in a private high school dormitory that housed 83 students. Case A began on October 1 and cases B and C were diagnosed on October 2. After approximately 10 days, 44 additional cases occurred in a one week time span. The county epidemiologist believed this second group of cases represented the same generation of cases, and was in the second incubation period after the occurrence of cases A, B, and C; none of the 83 students was known to be immune. What is the secondary attack rate?

Answer 1

The secondary attack rate is 55%

Explanation:

Total number of students = 83

Primary cases: cases A+B+C = 3 primary cases.

Secondary cases = 44

Total cases = 44 + 3 = 47

To find the secondary attack rate, we are to assume that the primary cases are now immune because they had the illness.

We have:

Secondary attack rate =
`(total cases - primary cases)/(number of susceptible - primary cases) * 100`

`= (47-3)/(83-3) * 100`

`= (44)/(80) * 100 = 55`

The secondary attack rate is 55%