Solid Hardwood, Engineered and Laminate Flooring - Mildew on Wood Floors...help

Hello, I tried looking up a response to this topic but I did not find one. Anyway, here goes. Sorry if it's redundant.

I decided to refinish the wood floors in two bedrooms in my house. When the carpet was pulled up to expose the wood underneath, there was obvious mildew/mold covering a majority of both floors. (It appears to be mildew due to it's white chalky appearance). Our floor guy didn't seem to think it was much of a problem. However, when the floor was sanded the mildewed areas left dark splotches over the floor that did not come up in the sanding. At this time, the floor is sanded but not yet stained and finished.

So my question is...should something be done to treat the floor (i.e. kill the mildew)? Or can I assume that the mildew is dead and will not continue to spread? Also, does anyone have any recommendations as to how to remove or lighten some of the stains left over?

Any help would be greatly appreciated. I visit this board often but this is my first post.
Thanks in advance!

Please dont assume the mildew/mold is dead just because you sanded or scraped at it. It is a living body and may produce some unpleasant surprises for you. Please inspect it further. If you feel you cannot do it yourself, then call a home inspector or contractor to do it for you. You need to see the other side of the floor and wall it touches and find out the true extent of your problem (unless of course, you intend to cover it up and abandon the property), mainly because of the health concerns. Good luck.

One time I was re-finishing a door at my wife's folk's place in Forida. The door was sanded down to bare wood, lying across a couple of saw horses in the front yard. We made a quick trip to the hardware store, and a short shower blew through the area getting the door wet. By the time we returned the sun was back out. So I figured "hey, just let it dry out" Unfortunately, the next time I looked at it that evening, it was completely peppered with black mildew colonies. I had never seen anything grow that fast before in my life.

My father-in-law was a builder, and knew what to do. We went back to the store and bought a two part wood bleach based on hydrogen peroxide. (The product was by Nutone -don't know if they're still in business) This was some nasty stuff - better get out your PPE. It turned that mahogony door almost the color of sun bleached driftwood, mildew and all. Then I simply restained and finished.
If your floor still shows discoloration after you sanded, then the mildew has penetrated down into the wood, and the wood bleach treatment is probably the only way to completely remove it. I would also add some mildewcide to your stain or finish .....Should be able to get some at a good paint store.