Don't they test you for STDs when you donate Plasma?

The reason I ask this is a person I know is pregnant and got a call from her doc yest that she has a treatable STD and the HPV virus on top of it. She'd never had a STD so she was upset of course. Well,we was trying to determine from her last check and his last check(without letting him know what we were really doing) how long they've had it....She's been with this guy 9 months. We find it odd that they had a girl who stayed with them for a couple weeks and she had this same STD. Yes, we think he might of cheated. Anyways, he told his pregnant girlfriend that he thought he was good because recently he donated plasma. I did think they tested you when you donated so they didn't get containmated plasma or whatever. If this is the case then he'd been clean since he'd donated back then (since dating the pregnant girlfriend) which means he'd cheated the way I see it.....Just trying to figure out where this STD came from. What you think? Don't they test for STDS?