million [ppm], 1 hour, at rest; Molfino et al., 1991). However, ozone did not alter the acute response to nasal challenge with allergen when higher ozone exposure levels were used (0.5 ppm ozone, 4 hours, at rest; Bascom et al., 1990). Epidemiological studies point to a contribution by outdoor air pollution to asthma exacerbations. Bates and Sitzo (1987) related increased hospitalizations for asthma to increases in air pollution in the Toronto region. Other studies are well summarized in a recent chapter (Bresnitz and Rest, 1988). Prevalence rates of bronchial responsiveness were associated with specific indoor pollutant exposures only among groups of people of lower socioeconomic status (Quackenboss et al., 1989b).

In summary, asthma is a prevalent disease whose magnitude includes a significant socioeconomic component. Indoor allergens are important at all phases of the disease process, from sensitization to disease onset and severity and prognosis. There is evidence that environmental control strategies can affect the severity of the disease. Nonallergic factors may modify the role of allergens in the disease process.

ALLERGIC RHINITIS

Rhinitis is inflammation of the mucosa (surface cells) of the nose; it causes such symptoms as sneezing, runny nose (rhinorrhea), postnasal drip, and congestion. Allergic rhinitis ("hay fever") is rhinitis caused by IgE-mediated inflammation. The contribution of allergy to this condition is assessed through the individual's medical and environmental history and by skin testing or blood serology to seek specific IgE against suspected allergens.

Other types of rhinitis that can cause similar symptoms include nonallergic rhinitis, vasomotor rhinitis, and infectious rhinitis. These diagnoses are made by the physician on the basis of clinical presentation and are considered when skin testing fails to show evidence for an allergic cause of the rhinitis or when symptom patterns suggest other diagnoses.

Prevalence and Incidence

The prevalence rate of allergic rhinitis is 15–20 percent, although estimated prevalence rates range from 8 to 43 percent (Hagy and Settipane, 1969). Some evidence suggests that the prevalence of allergic rhinitis is rising (Barbee et al., 1987). Incidence rates are highly variable, and are considered untrustworthy at present. Absenteeism and other impacts have not been adequately assessed.

Risk Factors

Allergy A high degree of skin test reactivity to common allergens correlates well with the rate of allergic rhinitis in population studies (Burrows



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