Recent research from the University of Queensland in Australia used 21 vacuum cleaners of various brands and ages in a small enclosed tunnel. Biologist Luke Knibbs's team compared the amount of bacteria, fungi, and dust in the air before and after the "cleaning."
Instead of cleaning, the vacuum only made things worse: after use, the air was full of fungi, bacteria and dust.
It is that the vacuum ends up releasing in the air part of the dirt that aspirates from the ground, like an aerosol. And these fungi and bacteria can arouse or result in a nasty allergy in you. One more excuse for the guests not cleaning the house! Think of another way because dirty house can't!