In house with 9 susceptible individuals 1 gets infected and other two get infected after two days what is the secondary attack rate -

Ans. is 'a' i.e., 25% SAR=No of exposed persons developing disease withinthe range of the incubation period----------------------Total number of exposed/susceptible contactx 100o The important features of SAR : -The primary case is excluded from both the numerator and denominator.Denominator is restricted to susceptible contacts of primary case.In denominator, person should be suscetible - Immune person (to disease) are not susceptible to develop the disease, So they are excluded.Disease should develop within the range of incubation period.o In this questionPrimary case -1Susceptible contacts - 8 (9-1)Number of susceptible developing disease (secondary cases) - 2# Thus SAR =28x 100 = 25%