TABLE 2-1 How Diseases Can Be Measured

Question

Appropriate Measure

How many people have asthma sometime in their life?

Cumulative prevalence

How many people have asthma in the United States today?

Current prevalence

How many people get asthma when they are children?

Age-specific incidence rates

Do children have more asthma than adults?

Comparison of prevalence rates for specific age ranges

Does allergy have a role in asthma?

Comparison of the probability of developing asthma among people with and without skin test reactivity

What proportion of asthma is attributable to allergy?

Attributable fraction

What proportion of asthma in children is attributable to house dust mite exposure?

Attributable fraction

Generally speaking, mild disease causes symptoms but only intermittently requires medication and infrequently alters life activities. Moderately severe disease may require regular physician visits, regular medication, and lost time from work or school. Severe illness may require admission to an intensive care unit, to a regular medical floor, or to a hospital emergency room (in decreasing order of intensity). In the case of allergic disease, death occurs relatively infrequently. Other measures that can be used to indicate the magnitude and dimensions of a particular disease (such as allergy) include quality of life, trends over time, and economic and psychosocial impact.

This chapter uses these and other measures to discuss the magnitude and dimensions of two aspects of allergic disease: sensitization and the specific allergic diseases themselves. Immunologic sensitization is important because it is an indicator of the population at greatest risk of developing allergic disease. The remainder of this chapter discusses the public health significance of immunologic sensitization and allergic disease in these terms.

IMMUNOLOGIC SENSITIZATION

Allergic disease develops through a series of steps that are becoming more clearly understood (Figure 2-1). As described briefly in Chapter 1, allergic disease occurs when a genetically predisposed or susceptible individual is exposed to an allergen and becomes immunologically sensitized. The occurrence of different types of sensitization can be ascertained by skin



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