What does the cryptic crossword clue "One studies diseases of poor oldies with impetigo (14)" mean?

The wordplay uses an anagram. anagram of OLDIES + IMPETIGO = EPIDEMIOLOGIST The answer is EPIDEMIOLOGIST.

One studies diseases of poor oldies with impetigo (14)

Daily Mail Cryptic #16723 | 8 Down | 2021-12-07 flower