In the "Stargate: Atlantis" episode 'The Seed' (S05E02), Dr. Jennifer Keller becomes infected with an alien pathogen that causes her to grow Wraith-like tendrils out of her body. Dr. Carson Beckett determines that the pathogen was developed by Michael on planet M2S-445, and that all surviving team members who visited the planet (Sheppard, Ronon, McKay) also tested positive for the pathogen. The problem with this is that Keller wasn't on that mission, and yet she was the first one to develop symptoms. They even address the fact that it isn't contagious, so Keller couldn't have gotten it by operating on Sheppard, for example.
WOOLSEY: Right now we're working under the assumption that this alien pathogen was present somewhere in that lab, possibly as part of one of Michael's experiments. When the building was destroyed, it was released.
SHEPPARD: We've been back for a month now! If it was going to spread to the general population, it would've already happened.
WOOLSEY: I know. Dr. Beckett is now fairly certain that it's not contagious.
She DID wake up in the lab with some kind of goo on her hand, but where did that come from? They weren't able to recover anything from Michael's lab, so there weren't any sample jars or anything.
How did Jennifer Keller become infected with the alien pathogen from M2S-445?