I'm not sure how useful it is to search for sexual transmission scenarios within a reference class populated entirely by the chaste.

Well, originally I suggested one scenario that would seemingly fall under this. I'm genuinely curious if someone can think of any others. Your suggestion of the Shiite temporary marriages is a good one, though based on some casual googling I just did, it appears that condoms are permitted by this particular religion.

I don't know whether churches would advise a repentent person who had cheated or had sex before marriage to then be celibate within their marriage. But if they tell them to keep having sex without protection then that specific action can be blamed for the results.

Only if they tell them to keep having sex without protection even if you have an STD. Or, perhaps, forbid testing for STDs.

It wasn't my intention to make or imply any value judgments and blame assignments in this context. I just asked if someone can think of a scenario that meets these conditions, as a mere question of fact and logic.

Only vaguely relatedly: in my callower youth, I enjoyed asking biblically inspired homophobes what grounds they had for sanctioning lesbians, since the go-to verses (Leviticus 18:22 and 20:13... also Romans 1:27, though that's less relevant for Jews) were so clearly targeting behavior among men. The sheer bewilderment in their responses was oddly enjoyable.

I count a lesbian couple with one child among my best friends.

I remain doubtful that there is a large incidence of female HIV positives who would not have been positive had they adhered to religious strictures against homosexuality. The HIV-homosexuality links is (according to this page) specific to the US, not to the rest of the world. There is a base rate fallacy at work.

(You know there are female homosexuals, right?)

Sure, but I'm guessing that Morendil was alluding to the lack of explicit prohibitions on female-female sexual acts in holy texts among the Abrahamic religions. This does not, of course, stop them from being considered a sin and the practitioners punished accordingly.

All three of them had a "sex == penetration with penis" mindset which made even acknowledging lesbians an "outside the box" problem.

The Christian bible, at least, does not have any explicit prohibition against female homosexual acts, just warnings against sexual immorality without female-female acts given as a specific example (Romans 1:26-27 would probably be the closest). I believe the same holds for Judaism and the Torah, with the Talmud and other rabbinical rulings against it (though nowhere near the same degree as male homosexuality -- no death sentences). AIUI, The Quran is in a similar position to the Bible -- 4:15 can readily be read to condemn female homosexual acts, but the words are somewhat generic so it can also be read instead as condemning other female sexual immorality. Hadith is practically silent -- it condemns "effeminate men" and "masculine women", as well as those who wear clothing traditionally used for the other sex, but again no explicit prohibition. There is a large body of Islamic jurisprudence however, and although the mentions of female-female sex are still rare, it is clear that it is forbidden under Sharia as it has been interpreted most places.