Slide 16: Risk Factors for Development
of Asthma
Risk factors are characteristics of people that increase the probability
that they will experience a specific disease or a condition associated
with a disease. Risk factors for asthma include genetic predisposition
and environmental exposures, such as house dust mites and environmental
tobacco smoke. However, just because a person is at risk for a disease
does not mean that he or she will develop that disease. Being aware of
the risk factors may help people take precautions to avoid acquiring
those diseases or conditions. Other risk factors to asthma can cause
someone with the disease to have an exacerbation (worsening) of
symptoms. We will talk about those risk factors later.
Slide 17: Genetic Characteristics
Atopy is a genetic factor characterized by the body's production of
immunoglobulin E after exposure to common environmental allergens. A
person with high levels of IgE in the blood is more likely to have an
allergic response when exposed to certain substances in the environment
- so high levels of IgE may predict the future development of asthma. If
a person has a parent with asthma, he or she is three to six times more
likely to develop asthma than someone who does not have a parent with
asthma.
Slide 18: Environmental Exposures
In 2000, the Institute of Medicine published the report "Clearing the
Air." This report reviews the evidence about indoor air exposures and
asthma as presented in the scientific literature. The report looked at
components that affected both the development of the disease itself and
the exacerbation of symptoms in someone who already has the disease.
Sufficient evidence of a causal relationship.
This means that the evidence is strong enough to document that
exposure to these substances causes the disease’s onset or
exacerbation.
Sufficient evidence of an association. This means that the evidence is strong enough to document an
association between the agent and the outcome has been observed in
studies in which chance, bias, and confounding factors can be
reasonably ruled out.
Limited or suggested evidence of an association. This means that the evidence suggests an association, but chance,
bias, and confounding factors cannot be ruled out with confidence.
Slide 20: Clearing the Air: Indoor Air
Exposures and Asthma Development
The Institute of Medicine committee concluded evidence was sufficient to
suggest a causal relationship between exposure to house dust mite
allergen and development of asthma in susceptible children. It also
found sufficient evidence of an association between exposure to
environmental tobacco smoke - also know as ETS or secondhand smoke - in
younger children and the development of asthma. This includes both
prenatal exposure to active maternal smoking and ETS exposure after
birth. Lastly, they found some evidence to link asthma's development
with exposure to cockroach allergen in preschool-aged children, and with
infections with respiratory syncytial virus (RSV).
Four additional exposures are associated with worsening the disease: dog
allergen, fungi or molds, rhinoviruses, and a high level of exposure to
nitrous oxides.
Evidence suggests an association between asthma exacerbations and
exposure to domestic birds, ETS in older children and adults,
formaldehyde, fragrances, and several respiratory infectious agents.
Let's look closer at some of these agents that the Institute of Medicine
identified and consider ways to reduce the level of exposure to these
agents in the home.
