Environmental Engineering Reference
In-Depth Information
were reported for black children. Since this survey was conducted, signifi-
cant increases in prevalence rates have been reported, with most of the
increase occurring in inner-city black and Hispanic populations. Unlike
adults, where asthma is more prevalent among females, male children have
higher prevalence rates than female children, with the difference being
twofold at certain ages.
Asthma is the major medical cause of absenteeism in school-age children.
It is also the leading cause of childhood hospital admission and long-term
medication use. Health-care costs for treatment of asthmatic symptoms
among all age groups in 1990 were estimated to be 6.2 billion dollars or 1%
of all health-care costs.
There is strong evidence that asthma is associated with sensitization to
common inhalant allergens. The primary allergens that appear to cause
sensitization are produced by dust mites in humid/wet regions; by the
German cockroach in many U.S. cities; and pet danders in northern and dry
regions. Sensitization appears to be the major risk factor for nonspecific
bronchial hyperreactivity and symptomatic asthma.
Though sensitization has been shown to be an important risk factor, no
definitive link has been established between allergen exposure and symp-
toms or severity of asthma. The absence of an apparent dose-response
relationship between symptom severity and current exposure may be due
to a variety of factors. These include individual differences in response,
inadequate exposure measurements, and concurrent exposures to a variety
of allergens.
The link between allergen exposure and asthmatic symptoms is an indi-
rect one. Significant decreases in prevalence and severity of asthmatic symp-
toms have been observed in hospital patients where allergen exposure is
low, and in a variety of intervention studies.
Asthma appears to be rare among aboriginal rural populations. Its prev-
alence increases dramatically with urbanization and life in more modern
housing. Increases in the prevalence of asthma may be due to changes in
lifestyle and housing, with associated increases in allergen exposures.
C. Hypersensitivity pneumonitis
Hypersensitivity pneumonitis, or extrinsic allergic alveolitis, is a group of
immunologically mediated lung diseases associated with repeated expo-
sures to a variety of biogenic aerosols that affect tissues in the periphery of
the lung.
Once sensitization has occurred, acute symptoms develop in response
to high concentration exposures. Respiratory and systemic symptoms occur
within 4 to 6 hours after exposure. These include fever, chills, a nonproduc-
tive cough, shortness of breath, myalgia (i.e., ache all over), and malaise.
Symptoms may persist for 18 to 24 hours with spontaneous recovery. In
office and industrial environments, symptoms diminish during the work
week and begin anew on reexposure after weekends and vacations.
