Duct cleaning involves loosening and removing dirt in ventilation system ductwork. Whether this practice has any effect on exposure to respiratory allergens (either positive or negative) has not been adequately investigated. Chapter 7 discusses duct cleaning in greater detail.
Aerosol control methods may offer some relief in the presence of continuing sources of specific microbial pollutants. Local exhaust that removes pollutants before they can circulate through room air is one of the best options. Machining fluid and bacterial enzyme aerosols have been controlled in this way. Circulating room air through either a central or console air cleaner can reduce particle levels to a steady state that depends on source strengths, dissemination rates, and the rate at which particles are removed by the cleaner. If a HEPA filter is used, all particles larger than 6 μm in size will be removed from the air that passes through the filter. If active sources (e.g., large dust mite populations, active fungus growth, cats) are present, it is likely that dispersal rates will exceed removal rates to a degree and that a steady state will eventually be achieved.
Other modes of aerosol removal depend on electrostatic precipitation and on devices that charge particles so that they become attached to environmental surfaces. The latter devices are not advisable for use with allergens because disturbance of the collecting surfaces (e.g., carpeting, upholstered furniture, walls) will reaerosolize the particles.
Overall, the fungus-associated allergies have been the least well-studied. Little data is available on the distribution of airborne fungal products, dynamics of human exposure, nature of the allergens, factors influencing the quality of skin test and immunotherapy materials, and the basic nature of fungus-related allergic disease.
Research Agenda Item: Initiate and conduct studies to determine the relative etiologic importance, geographic distribution, and concentrations of airborne fungus material associated with indoor allergy.
Fungi grow indoors in damp environments such as basements, window sills, shower stall surfaces, and in dust. Fungal spores and other effluents become airborne indoors when disturbed by air movement and normal human activities. The composition of aerosols of fungus-derived particles