Microbiologic air contamination plays, among other factors, a role in building associated illnesses i.e., hypersensitivity diseases, bacterial and fungal infections, sick building syndrome. Airborne microorganisms are separated into obligate parasites, such as the viruses and a few bacteria, that must find a suitable host within a brief period, and facultative saprophytes that are usually found in living hosts an/or in the environment (primary and opportunistic pathogens).