To get the "infected" title someone wearing it has to knife you.
To get "std"title you have to knife someone wearing the "infected" title.
I've been running around for the last week or so with marathon pro,lightfoot & commando pro trying to spread the "infected" title,have given it to 100+ people(if they didn't allready have it). Still don't see it being used much though so I havn't had the chance to get the "std" title yet.