House is completely covered with black mold

We went on vacation for a week and just returned. When we left we had no problems with out house. We locked the doors and left. When we got home last evening the first thing I noticed was the siding had a black substance covering about half the house. When we walked in the door, we were shocked. The entire interior of the house was black with mold. In some places the mold is a foot thick. Everything is coated with this mold, the walls, floors, ceilings, lights, furniture, everything. Even inside the refrigerator the food is all black. We just woke up, and now our bodies are covered with this mold, and it itches too. What could cause this? There are no plumbing leaks, no roof leaks, nothing like that.