Indoor Air Quality Issues by David L. Hansen

Author:David L. Hansen
Language: eng
Format: epub
ISBN: 9781351438919
Publisher: CRC Press

Allergic Diseases

The function of the immune system is to recognize “foreign” proteins (called antigens) and to form antibodies (also called immunoglobulin), as part of the body’s defense against infection and disease (Clayman 1989). Microorganisms and/or their by-products can act as antigens and cause various allergic reactions. Allergies are inappropriate or exaggerated reactions of the immune system to foreign proteins, which may not actually be harmful; these reactions are termed hypersensitivity reactions.

Allergic reactions do not occur during the first exposure to an antigen. Rather, they occur only on the second or subsequent exposures to the biomatter, after the first contact has sensitized the body (Clayman 1989). During the first exposure, the antigens (in this case microbial material) provoke the immune system to produce specific antibodies, namely, immunoglobulin E or G. These antibodies coat the mast cells present in the stomach, lungs, and upper respiratory airways. At this first exposure, the person may not experience any ill effects, but when the antigen is encountered again, it binds to the antibodies and causes the mast cells to release chemicals that produce the allergic response (Clayman 1989). Allergic responses to aerosolized microbial matter include hypersensitivity pneumonitis, asthma, and rhinitis (hay fever) as well as mucous membrane irritation and chronic bronchitis.

Hypersensitivity pneumonitis (HP) causes fever, chills, and cough 8 to 12 hours after exposure. These symptoms disappear after one or two days but reappear after another exposure. Once an individual develops a sensitization of the respiratory tract, continued exposure to the antigen can lead to permanent disease. However, it is unclear how long the latency period is between exposure and onset of symptoms. Both atopic (a predisposition to various allergic reactions) and nonatopic occupants can get HP from exposure to specific organisms. There are numerous case studies of building-related HP outbreaks due to exposure and subsequent sensitization to microbial aerosols (Rose 1996).

In the United States alone it is estimated that more than 10 million people suffer from asthma. There are two main types of asthma: extrinsic, in which an allergy to an external factor triggers an attack, and intrinsic, in which there is no apparent external cause (Clayman 1989). The main symptoms are breathlessness, wheezing, a dry cough, and a feeling of tightness in the chest.

Allergic asthma and rhinitis (hay fever) can be caused by airborne fungus spores (ASHRAE 1989). But it is difficult to ascertain if a building-related source of microbial matter is in fact causing the asthma, because numerous other factors such as chemical irritants and cold air can induce asthma.

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