A great many common abbreviations behave perfectly well in any fiction or nonfiction context, including dialogue, when the general guidelines in CMOS are observed: Mr., Ms., CEO, p.m., PhD, UFO. Editors should have no quarrel with them, as long as they’re styled consistently.
At paragraph 6.20, the 17th edition of The Chicago Manual of Style notes that the abbreviation etc. (et cetera, literally “and others of the same kind”) and such equivalents as and so forth and and the like are preceded by a comma. In a slight departure from previous editions of CMOS, such expressions are
This month’s workout, “Abbreviation of Names and Titles,” centers on CMOS 17, paragraphs 10.11–27.
Frequently, writers to the “Chicago Style Q&A” express the belief that when an abbreviation is introduced in a document, it must be introduced once and once only (when the term first appears) and that thereafter the spelled-out term must never be used again.
Today’s workout, “Abbreviations Overview,” centers on the information found in sections 10.1–10.10 of CMOS.