Because of the ubiquity of the aspergilli within the environment, man is constantly exposed to these fungi. The diseases caused by species of Aspergillus are relatively uncommon and are rarely found in individuals with normally functioning immune systems. However, due to the substantial increase in populations of individuals with active immune suppression, such as individuals with HIV, chemotherapy patients and those on corticosteroid treatment, contamination of building substrates with fungi, particularly Aspergillus species have become an increasing concern. Aspergillosis is now the second most common fungal infection requiring hospitalization in the United States.
The most frequently encountered opportunistic Aspergillus pathogen, Aspergillus fumigatus, is seen most abundantly in decomposing organic materials. Because it grows well at temperatures up to 55*C, self – heating compost piles provide an excellent environment for the fungi. compost made up of chipped branches and leaves will often yield a massive and virtually pure culture of A. fumigatus. A. fumigatus has been reported to be the major organism isolated from air samples obtained near compost sites. People who handle compost or decomposing haystacks often develop hypersensitivity to spores of Aspergillus and after exposure may suffer a severe allergic response.
Aspergillus flavus is the second most frequently encountered fungi in cases of infection with Aspergillus species. In addition to causing infections, Aspergillus flavus is also renowned for its production of aflatoxin, one of the most potent carcinogens known to man. Concern about aflatoxin began in the 1960s after some 100,000 turkey poults in Great Britain died as a result of ingesting feed tainted with aflatoxin. When it became evident that aflatoxin was highly carcinogenic most industrialized countries established tolerances for aflatoxin levels in food and feeds. The risks associated with airborne exposure to aflatoxin in contaminated buildings, as with other mycotoxins, has not been adequately studied.
Aspergillus niger is the third most common aspergilli associated with disease and is more common than any other Aspergillus species within the genus and is found in and upon the greatest variety of substrates. It is commonly associated with “fungus ball”, a condition wherein fungus actively grows in the human lung, forming a ball, without invading lung tissue.
Because invasive aspergillosis occurs most frequently among highly immunosuppressed patients, the presence of Aspergillus spores in hospital air has important implications. Aspergillus spores frequently occur in hospitals throughout the world and a number of severe outbreaks resulting in deaths due to disseminated invasive aspergillosis have been reported following renovation activities in hospitals. a study of 39 bone marrow transplant patients who resided in rooms equipped with whole wall laminar flow HEPA filtration units reported no cases of nosocomial aspergillosis. In sharp contrast, 14 cases of nosocomial aspergillosis in 74 bone marrow transplant recipients occurred in patients housed elsewhere. It is critical that aequate engineering controls are implemented during renovations at hospitals or at any facility the immunosuppressed frequently occupy.
Stachybotrys thrives on water damaged cellulose rich materials in buildings such as sheet rock paper, ceiling tiles, cellulose containing insulation backing and wall paper. Almost without exception an extended saturation time and/or consistently high levels of humidity are required for this fungi to proliferate. Thus in a majority of cased where Satchybotrys is found in buildings the water damage event(s) that has occurred often goes unnoticed, or often as not, ignored by maintenance personnel that are unaware of the implications of such contamination. In sharp contrast, single or sudden water damage events that occur where drying of water damaged material takes place more quickly tend to support the growth of more xerophilic fungi such as Penicllium and Aspergillus species.
The presence of Stachybotrys fungi in buildings is significant because of the mold’s ability to produce mycotoxins, metabolites of fungi that can cause adverse health effects in humans and animals. Although most molds produce mycotoxins, those produced by Stachybotrys are extremely toxic, are suspected carcinogens and are immunosuppressive. Exposure to these toxins can occur through inhalation, ingestion of dermal exposure. Symptoms of exposure to Stachybotrys toxins include dermatitis, cough, rhinitis, nose bleeds, cold and flu symptoms, headache, general malaise and fever. Much of what is known about stachybotrystoxicosis has been gleaned from observation of exposed livestock. Animals exposed to high levels through ingestion of contaminated forage die rapidly due to massive hemorrhaging, both internal and external. Exposure to lower levels over time leads to severe immune system suppression since afflicted animals often suffer from septicemia and succumb to a number of opportunistic infections As a general rule, air sampling for Stachybotrys yields unpredictable results because of a number of factors. First, when significant Stachybotrys contamination is present, other fungal contaminants are usually present as well. When conducting sampling using Andersen N-6 generally other fungal contaminants will tend to overwhelm the Stachybotrys spores in culture, due to their more rapid growth rate, even when using selective media such as cellulose agar. In addition, most commonly encountered fungal spores such as those of Aspergillus and Penicillium tend to be much more easily aerosolized than Stachybotrys thus further amplifying the recovery of the less significant contaminants. typically under active growth conditions, the spores of Stachybotrys adhere to one another in a sticky sack, making passive aerosolization even more difficult. However, once a Stachybotrys contaminated surface has dried for an extended period of time the sticky sack desiccates and the spores are released much more readily.
Because of these factors, a visual inspection of the subject building is the best method of identifying a potential Stachybotrys contamination problem and requires a trained eye. Recognizing that Stachybotrys constant moisture and cellulose for growth helps the inspector narrow down potential sources. Stacybotrys typically appears as a sooty black fungus occasionally accompanied by a thick mass of white mycelia. Bulk or surface sampling of suspect materials should be conducted using caution and removed to the laboratory for identification by light microscopy. New inexpensive techniques are also currently available to measure specific mycotoxins produced by Stachybotrys and can assist the inspector in determining the toxicity of the strain isolated. Site specific analyses should be discussed with the inspector’s laboratory.