Denominator while calculating the secondary attack rate includes-
The denominator consists of all persons who are exposed to the case. More specifically the denominator may be restricted only to susceptible contacts if means are available to distinguish the susceptible persons from the immune. (refer pg no 100 park 23rd edition)
All the people living in next fifty houses
All the close contacts
All susceptible among close contacts
All susceptible in the whole village
Epidemiology