According to NPR(listen to the audio), the normal processes that keeps mold at bay when residents enter and leave a building, are no longer present when the homes across our nation are sitting vacant due to foreclosures.
In a foreclosed home without electricity, ventilation or occupants to detect moisture issues mold is beginning to grow.

“A full quarter of his work now comes from moldy, foreclosed homes where the electricity has been shut off. No electricity means no sump pump or dehumidifier for months, even years, and that often means mold — slimy black or green patches creeping up drywall and blanketing bathroom fixtures.”

A Manifestation of the recent Foreclosures

Realtor Rebecca Terakedis has been showing a number of vacant, foreclosed, moldy homes to buyers.

“I have a release form that I use, and if the property has got a lot of mold in it, I don’t even let my own husband go in it without signing this disclosure because I don’t want the liability,” she says. “I had one really interesting [one]. It was the middle of winter. There were icicles coming out of the windows above the garage, no heat, but it was 80 degrees inside of the house because it was self-composting.” states Rebecca Terakedis.

The whole process of banks foreclosing on homes, people loosing their homes allows the bills to go unpaid and the process takes a lot longer than anyone wants and this promotes the mold growth problems.  Another Realtor states, ” banks won’t sell a home for less than the mortgage note and so home sit and mold continues to grow.

“I had an offer on a house with Bank of America where they have agreed to do a short sale, and it’s been over two months, and they haven’t even responded to the offer,” she says. “They don’t have enough staff to move it along — too backed up. They don’t have enough qualified people who know what they’re doing, and, you know, it’s in a pile somewhere.”

Charges of faulty paperwork have slowed the pace of foreclosures in recent months, and that may be exacerbating the mold problem as those houses sit and bake through the long, hot summer.
http://www.npr.org/2011/07/13/137629788/as-number-of-foreclosed-homes-grows-so-does-mold?source=patrick.net#recommendationCntHref