30 Something Baby Doc

I saw a 19 year old patient today for her first pelvic exam. She said she had sex once and would never do it again soon. Regardless I was still able to talk her into using birth control and counseled her on the value of safe sex. She swore to me that condoms were used during this brief encounter. But when I examined her, a foul smelling greenish yellow purulent (pus like) discharge was oozing from her vagina. Under microscopic inspection, it turns out she had contracted Trichomonas (A very nasty STD where small creature can be seen swimming around under higher magnifications). The latter is less likely if condoms were used.
I asked her if the condom had burst or come off? She then stated that intercourse had commenced with out a condom and her partner put the condom on just before he ejaculated (.....very thoughtful indeed).