Rashi on Leviticus 22:5/רש"י על ויקרא כ״ב:ה׳

1בכל שרץ אשר יטמא לו [OR WHOSOEVER TOUCHETH] ANY PROLIFIC CREATURE BECAUSE OF WHICH (לו) HE MAY BE MADE UNCLEAN — This means: who touches any שרץ of the minimum size that is capable of communicating uncleanness, viz., a particle of the size of a lentil (cf. Sifra, Emor, Chapter 4 4; Chagigah 11a).

2או באדם OR A HUMAN BEING — a dead person (Sifra, Emor, Chapter 4 4).

3אשר יטמא לו BY WHOM HE MAY BE MADE UNCLEAN - i. e. by touching the minimum size of a portion of the dead person which is capable of transmitting uncleanness, and this is, a portion as large as an olive (Mishnah Oholot 2:1).

4לכל טמאתו WHATSOEVER UNCLEANNESS HE HATH — This is intended to include in the prohibition of eating holy things one who has touched a man or a woman who has an issue, or who has touched a נדה or a woman in childbirth (Sifra, Emor, Chapter 4 4).