In recent years, the health effects from exposure to fungal growth within built environments have been a subject of intense public concern. Fungi can cause a number of infectious and noninfectious conditions. Several basic mechanisms are responsible for these health effects including, but not limited to, immunologic (IgE-mediated allergic response), infection, and toxic effects from ingestion, direct skin contact, inhalation of spores, and mycelial fragments.1 It is common for several mechanisms to contribute toward the pathogenesis of a fungal-induced disease.
The type and severity of symptoms are related to the type of fungal spores, genera and speciation, and growth pattern. Susceptible individuals (e.g. people with allergic conditions or immunocompromised) are more susceptible than healthy individuals. Fungi also produce a variety of volatile organic compounds; the most common being ethanol, which is responsible for musty odors associated with fungal growth. Exposure to microbial growth is associated with a variety of upper and lower respiratory tract symptoms.
Microbial growth will always be presented indoors. Exposure to a normal ecology of fungi can occur from outdoor sources and surfaces of skin, clothes, and shoes of people. These exposures are considered the normal mycoflora. When moisture problems occur inside residential, commercial, or institutional dwellings, the resulting fungal population can be quite different. Moisture in combination with nutrients and optimal environmental conditions can cause hyphal fragments to flourish and grow into a mycelial mass. As the mycelial mass grows, conidia are produced from the fungal population. The spores can become dispersed within the indoor environment by wind or air pressure differentials, insects, and sometimes by water droplets.2, 3
Fungal types are divided into distinct categories: common outdoor (CO) fungal species and those indoor species (IS) amplified by water or moisture intrusion in indoor environments. Some of the most common fungi found outdoors include species of Cladosporium, Alternaria, Epicoccum, yeast (Rodotorula), Ascospores, Basidiospores, Paecilomyces, Pithomyces, and Ulocladium. Indoor indicating species of fungi include: Acremonium, Aspergillus, Aureobasidium, Chaetomium, Fusarium, Penicillium, Phoma, Stachybotrys, and Trichoderma. Besides these fungi; gram-negative bacteria, streptomycetes, actinomycetes, and other thermophilic bacterial should be considered when evaluating the microbial growth within the interior envelope.
Under normal conditions, the mycoflora found in indoors is similar to the outdoor environment. Wind can cause the fungal spores, hyphal, and mycelial fragments in the soil, leaf litter, or decaying vegetation to become airborne. Outdoor airborne concentrations, under these conditions, can be somewhat higher than indoor air concentrations. Alternatively, snow and heavy rain can dramatically decrease the outdoor airborne concentration of fungi. Caution should be used whenever comparing the outdoor to indoor air concentrations.