Supposedly had cured from it, but turns out it wasn't true.
It's hard to say why, but a lot of suspicions point towards mutation with his previous myth Aram.
Or
Could be a whole new reason entirely.

But if he has been infected the entire time it could be possible, he has control over it and strange connection to it. Despite the strand originating from new mexico, Kayda's hive it was kept undetected by everyone (or mostly undetected).

The strand does show signs of mutation or more so adaption, thus why the cure didn't work on it.

The outbreak shows signs of aggression towards others it deems as a threat, and Marius goes through a huge personality switch. He develops extra appendages likes a  spider on his back:

He can makes webs and form out spikes most like other outbreak.

It's believed the outbreak still views as humans and rainbow as threats, thus responding a lot like the first generation that hit new mexico. Thus being protective of other outbreak and aggro to others.
It all makes since how jäger is able to detect changes within different strands, communicate, and immune to other strands.

He sets himself apart from his own kind, because of the changes the outbreak did. Of course he is not good at socializing, but a lot of it was the fact he was infected. He kept this a secret because if people found out about it, he would have to go under the REACT protection protocol. In other words quarantined and locked up for a long time, until cured.

Despite the self control he has this is something Harry can't exactly ignore, because outbreak reacts differently than the dragons do.

If the operators got infected they always show aggression, and savagery thus why it was ordered they are to be clean.
Jäger knows this but keeps it quiet, or more like his outbreak keeps him quiet about it.

(Wip)

-bloodhound-