And you are right not to believe that, because that's not what it said. It didn't say 110M plus people have (one or more) STDs, it gave a count of instance of infections. If Sally Slut gets the clap, takes her antibiotics until its gone, then gets the clap again, that's two infections. If Bathhouse Billy, whose immune system is compromised by AIDS gets secondary infections of syphilis, gonorrhea, chlamydia, herpes and genital warts, that's six infections.
Remembering that they are probably counting all the HPV infections that show up as abnormal Pap smears (and maybe even presumptively counting another infection for each sex partner she reports) and chlamydia (neither of which were in the list of venereal diseases we were taught in school back in the day before STD became the politically correct term), and that a very promiscuous person can account for multiple infections, the estimate sounds reasonable
I STILL DON’T BELIEVE IT!