Alternaria (all-tur-nair’-ee-uh) – common allergen/contaminant/opportunistic pathogen, one of the most common molds found worldwide in soil and on plants and can commonly be found indoors (frequently appearing black on window frames). It is an important airborne allergen and a common agent for hay fever, asthma, and other allergy-related symptoms.

Aspergillus (as-per-jill-us) – allergen/contaminant/opportunistic pathogen, commonly found in the environment around the world. It comprises approximately 200 species and can appear in almost any color. Though commonly found on cultures, tape-lifts, and air samples, its spores are indistinguishable from Penicillium on non-cultured samples (like tape-lifts and air-o-cells) unless the conidiophore is present. Health effects vary by species, but many species are reported to be allergenic. Some species produce toxins that might have significant health effects on humans. Aspergillus is one of the most infectious of molds, but infections are not common in normal immune systems. Aspergillus spp. are well-known to play a role in three different clinical settings in humans: (1) opportunistic infections; (2) allergic states; and (3) toxicoses. Immunosuppression is the major factor predisposing to the development of opportunistic infections. These infections may present in a wide spectrum, varying from local involvement to dissemination and as a whole called aspergillosis. Among all filamentous fungi, Aspergillus is in general the most commonly isolated one in invasive infections. It is the second most commonly recovered fungus in opportunistic mycoses following Candida. Construction in hospital environments constitutes a major risk for the development of aspergillosis particularly in neutropenic patients. Aspergillus versicolor can be found mostly in temperate areas in air, house dust, foods, soils, hay, cotton, and dairy products. Its presence in indoor air often indicates signs of moisture problems in buildings, as it is readily found in water-damaged building materials. This species produces the mycotoxin sterigmatocystin, which is reported to be carcinogenic to the liver and kidney, and it can cause such symptoms as diarrhea and upset stomach. It also produces the volatile organic compound (VOC) geosmin, this compound causes irritation of the mucus membranes of humans and pets; also causing the characteristic musty, earthy odor often connected with moldy houses.

Chaetomium (kee—toe-me-um) – contaminant, rarely involved in systemic and cutaneous disease and sometimes reported to be allergenic. Some species can produce toxins, and there is some research interest on whether these toxins can cause cancer. Primary IAQ importance is currently related to that it will grow in the same conditions as Stachybotrys (wet cellulose) and amplified amounts in indoor air could be a warning that conditions do exist for Stachybotrys growth. Many times on damp sheetrock paper, colonies of Chaetomium and Stachybotrys will be growing on top of one another or side by side (this can also be an important consideration when doing tape lifts of sheet rock because most of the time the colonies are not distinguishable by the naked eye – the small area that is sampled might be a pure colony of just Chaetomium even though numerous colonies of Stachybotrys might exist.)

Fusarium (few-sarh-ee-um) – contaminant / opportunistic pathogen, found on fruit, and grains and is common in soil. Indoors, it sometimes contaminates humidifiers. Associated with eye and various other infections in immunocompromised individuals and particularly burn patients. Produces a variety of toxins mainly important when ingested, particularly through contaminated grain products.

Stachybotrys (stack-ee-bought-ris) – contaminant, found indoors, primarily on wet cellulose-containing materials. It is the “toxic black mold” that has garnered much media attention. Some species produce a potent toxin that is lethal to animals, though the dose effect on humans is not clear. One species produces a toxin linked to the bleeding lung deaths of several infants. A host of other toxic reactions in humans are also linked to it, but many of these require further study. Stachybotrys is sometimes difficult to detect indoors because many times it will grow unseen on the back of walls or in the wall cavity with little disturbance that would cause it to be detected by routine air sampling. This is potentially also when it is of most health concern: when it covers entire wall areas and constantly produces toxins undetected. Non-cultured lab analyses (air-o-cells and tape-lifts) usually are the proper method of identification because Stachybotrys does not grow or compete well on most culture plate media, and it is reported that even non-viable spores can be toxigenic.