Mildew

[FloorCareMD]

I take my youngest son to an allergists Dr.'s office every week. Carpets look dirty but they have a janitorial company (you know the kind, own a few rags and a sponge mop, and pay all helpers as subs) do all their cleaning.
When we went there yesterday, there was the strongest mildew (or mold?) odor I ever smelled throughout the building. The receptionist said that they just had their carpets cleaned.
I snooped some and only info I know is they used a 175 wallbanger and regular extraction soap.

Now, here is the question..... What would /could one do to remove the odor and the source?
Is it possible for a low moisture cleaner to do so or even the use of a portable extractor?

thanks