Work out secondary attack rate instantly with clear inputs, formula shown and shareable results.
Divides secondary cases by the susceptible contacts, excluding the primary cases themselves from the denominator.
Secondary attack rate
SAR (%) = secondary cases / (total contacts - primary cases) x 100
They were the source of exposure, so they were never susceptible contacts within the household.
Household SAR measures transmission in a closed high-contact setting and usually exceeds the community average.