In this article the authors see that in men who have sex with men, those who douche (enemas) before sex are more likely to be infected with an STI / HIV compared to those who do not. Why did you see this difference? It is not clear if there is more anal sex without a condom in the douching group, or if it is the same douche that damages the rectal mucosa and leaves the man more susceptible. If I find more publications this year on this topic I will let you know.
Li P et al. Association between rectal douching and HIV and other sexually transmitted infections among men who have sex with men: a systematic review and meta-analysis. Sex Transm Infect. 2019 Sep; 95 (6): 428-436. doi: 10.1136 / sextrans-2019-053964. Epub 2019 May 9. PMID: 31073094.