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Fungi are ubiquitous in all environments and play a critical ecologic role by decomposing organic matter. “Mold” is the common term for multicellular fungi that grow as a mat of intertwined microscopic filaments (hyphae). Molds are pervasive in the outdoor environment but may also be present indoors under certain conditions, primarily in the presence of excessive moisture from leaks in roofs or walls, plant pots, or pet urine. The most common indoor molds are Cladosporium, Penicillium, Aspergillus, and Alternaria. Other molds that can grow indoors include Fusarium, Trichoderma, and Stachybotrys; the presence of these molds often indicates a long-standing problem with water leakage or damage.

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  1. Mechanism of toxicity. Molds and other fungi may affect human health adversely through three processes: allergy, infection, and toxicity.

    1. Allergy. Outdoor molds are generally more abundant and important in allergic disease than indoor molds. The most important indoor allergenic molds are Penicillium and Aspergillus species. Outdoor molds, such as Cladosporium and Alternaria, often can be found at high levels indoors if there is abundant access for outdoor air (eg, open windows). Excessive moisture or water damage in homes and buildings can lead to enhanced growth of allergenic fungi.

    2. Infection. Several fungi cause superficial infections involving the skin or nails. A very limited number of pathogenic fungi (eg, Blastomyces, Coccidioides, Cryptococcus, and Histoplasma) can infect nonimmunocompromised individuals. Persons with severe immune dysfunction (eg, cancer patients on chemotherapy, organ transplant patients on immunosuppressive drugs, patients with HIV infection) are at increased risk for both the pathogenic fungal infections listed above and more severe opportunistic fungal infections (eg, with Candida and Aspergillus).

    3. Mycotoxins and glucans. Some species of fungi are capable of producing mycotoxins, whereas most molds have one of a group of substances known as glucans in their cell walls. Serious veterinary and human mycotoxicoses have been documented after ingestion of foods heavily overgrown with toxigenic mold species. Inhalational exposure to high concentrations of mixed organic dusts (often in occupational settings) is associated with organic dust toxic syndrome (ODTS), an acute febrile illness. This self-limited condition generally is attributed to bacterial endotoxins and potentially to mold glucans rather than to mycotoxins. Exposure to mycotoxins has been documented in indoor environments, but currently there is insufficient evidence to confirm that such exposures result in human disease. Cases of acute idiopathic pulmonary hemorrhage (AIPH) in infants have been attributed to home contamination by Stachybotrys chartarum, but this apparent association has not been definitively confirmed.

    4. Volatile organic compounds (VOCs), including low-molecular-weight alcohols, aldehydes, and ketones, are generated by molds and are often responsible for the musty, disagreeable odor associated with indoor molds. A role for these VOCs in some building-related symptoms is possible.

  2. Toxic dose. Because mycotoxins are not volatile, exposure would require inhalation of aerosolized spores, mycelial fragments, or contaminated substrates. The toxic inhaled dose of mycotoxin for humans is not known. Based on experimental data from single-dose in vivo studies, Stachybotrys chartarum spores (intranasally in mice or intratracheally in ...

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