ABSTRACT
Although no standards have been set in the United States for limits on airborne microbial levels, many other countries are adopting or already mandating certain limits (see Chapter 18). Even without standards, the measured levels of airborne microbes in hospital air provide a basis for understanding the epidemiology and etiology of airborne nosocomial disease transmission. It has been said that for pathogens no airborne concentration can be considered safe for human occupancy, but completely sterile air may be an almost unachievable ideal whenever human occupants are present. At best we can only hope to reduce airborne concentrations of pathogens to levels that will reduce the risk of infection. In order to know whether disinfection techniques are effective we Ÿrst must know what the normal levels of airborne microbes are for any given hospital environment. The following sections describe the results of airborne sampling in various hospital environments. It should be noted, and will be demonstrated in later chapters, that the normal levels of requisite air Ÿltration should completely eliminate virtually all fungal spores and environmental bacteria, and therefore the presence of these environmental microbes in the indoor air of hospitals indicates either a failure of the Ÿlters to perform or, more likely, the fact that there are alternate pathways by which such microbes may enter the hospital.
