The mold Alternaria is a well recognized allergy causing fungus. Alternaria spores can be detected from spring through late fall in most temperate areas, and can reach levels of thousands of spores per cubic meter of air. Alternaria spores can be at their highest concentrations during dry, windy conditions that are ideal for the spores to become airborne. Alternaria is currently comprised of about 40-50 species. It is commonly isolated from plants, soil, food, and indoor air. One of the species, Alternaria alternata, has been isolated from numerous kinds of organic materials in damp situations, including textiles, stored food, canvas, cardboard and paper, electric cables, polyurethane, jet fuel, sewage and effluents.
Airborne spores of Alternaria alternata and Alternaria tenuissima are found in very high numbers in the outdoor environment during summer. The presence of Alternaria together with other molds such as Stachybotrys spp, Aspergillus spp, in indoor environment is indicative of humid conditions.
Alternata is not commonly isolated from indoor building materials and in most instances spores found in indoor air environment may have originated from outdoor sources. A closely related mold, Ulocladium chartarum, which is very common in indoor environments is frequently misidentified as Alternaria alternata. Ulocladium chartarum is common on wallpaper and drywall, and has been isolated from emulsion paint, polyurethane, plywood and manila fibre. A. alternata shows significant morphological variation and is believed to be a species complex meaning that it is an amalgam of closely related strains rather than a single homogeneous species.
Alternata is recognized as an important allergen with airborne spores and mycelial fragments being responsible for the allergic symptoms in individuals with rhinitis or bronchial asthma. Alternaria sensitivity can also lead to severe and potentially fatal asthma. Studies have shown that up to 70 % of mold-allergic patients have skin test reactivity to Alternaria. It has also been shown that prolonged heavy exposure to Alternata spores and mycelial fragments mimics that of other allergens such as cat dander and dust mites. It has also been recorded as an opportunistic pathogen causing skin diseases particularly in immunocompromised patients such as the bone marrow transplant patients.
The presence of Stachybotrys, Chaetomium, Trichoderma, Aureobasidium and also actinomycetes and other bacteria in an indoor environment is generally indicative of wet conditions, not just high humidity or condensation on indoor surfaces.