7 cases of hepatitis A occurred among 70 children attending a child day care center. Each infected child came from a different family. The total number of persons in the 7 affected families was 32. One incubation period later, 5 family member of the 7 infected children also developed hepatitis.
- Calculate the attack rate.
- Is this primary of secondary attack rate?
1. Secondary attack is used to measure the frequency of new cases of disease among contacts of known cases.
Secondary attack rate = Number of new cases/Population at risk x 100
= 5/(32-7) x 100 = 20%
2. It is secondary attack rate