A leprous plague could infect a house during the days of ancient Israel in the Land of Canaan.
The owner had to go to the priest to report what the owner suspected might be leprosy, and then he would have to empty the house before the priest could examine the structure. This way nothing else in the house would become unclean.
If the priest discovered ingrained streaks, greenish or reddish, in the suspected plague (Leviticus 14.37), he was to do the following,
“then the priest shall go out of the house, to the door of the house, and shut up the house seven days. And the priest shall come again on the seventh day and look; and indeed if the plague has spread on the walls of the house” (Leviticus 14.38, 39),
the priest had to remove those infected stones and take them to an unclean place.
Just as humans were isolated seven days, so was a home.
This was sufficient to decide whether the plague was leprosy.