Environmental Engineering Reference
In-Depth Information
caused by gas-phase irritants. Likewise, asthma is a major public health
concern because of its relatively high and increasing prevalence rate and
the seriousness of the disease. The nature of these ailments is described
below. In addition, special attention is given in this chapter to illness and
exposure concerns associated with bacteria and bacterial products, viruses,
and allergen-producing arachnids, insects, and mammals. Mold is discussed
in Chapter 6.
I. Illness syndromes
A. Chronic allergic rhinitis
Chronic allergic rhinitis or common allergy is a relatively nonserious illness
caused by exposures to substances that have antigenic/allergenic properties.
In sensitized individuals, inhalation exposures to specific allergens result in
inflammatory symptoms of the nose, throat, sinuses, eyes, and upper airways
characterized by congestion, runny nose, phlegm production, sneezing, and
in many cases, coughing.
Inhalant allergies are commonly caused by immunologic sensitization
to dust mite antigens, mold spores and hyphal fragments, pet danders, and
pollen. They may also be caused by exposure to antigens produced by insects
(e.g., cockroaches), birds, rats, and mice.
Symptoms are produced as a result of immunological sensitization and
subsequent exposures that produce inflammatory responses by one of four
different mechanisms. The most important of these is the production of IgE
antibodies in response to exposures to an antigenic substance, which can
cause a detectable immune response. Antigens that evoke an IgE response
are described as allergens.
Antigens/allergens are relatively large molecules (typically proteins).
However, some highly reactive compounds, such as formaldehyde (HCHO),
toluene diisocyanate (TDI), and trimellitic anhydride (TMA) can complex
with proteins to produce hapten antigens that induce allergenic responses.
Allergy mediated by IgE antibodies is very common. Approximately
40% of the population of the U.S. has been estimated to have IgE antibodies
specific for one or more allergens, with 50 to 65% of these experiencing
clinical symptoms. Approximately 10% of the U.S. population has experi-
enced severe chronic allergic rhinitis; that is, symptoms severe enough to be
diagnosed and treated by a physician. Accordingly, tens of millions of indi-
viduals in the U.S. experience seasonal or persistent allergy symptoms each
year. The prevalence rate for chronic allergic rhinitis appears to have
increased significantly over the past two decades.
Sensitivity to allergens varies with age. In children under the age of 5,
sensitivity to inhalant allergens has been reported to be about 22%, rising to
45% between the ages of 5 and 13. However, peak sensitivity reportedly
occurs among individuals in the age range of 20 to 45 years.
