Then the priest shall come and look
On the seventh day of the second week; though, according to Maimonides F15, this was at the end of the third seven day, or on the nineteenth day from his first inspection into it; the seventh day being reckoned for the last of the first week, and the first of the second, and so on: and, behold, [if] the plague be spread in the house;
after all the above precaution is taken; it [is] a fretting leprosy in the house;
like that in the garment, (See Gill on Leviticus 13:51): it [is] unclean;
and so not to be inhabited.
F15 Hilchot Tumaat Tzarat, c. 15. sect. 1, 2.