et al., 1976). For example, in the study by Burrows et al. (1976), the fraction of the population with the lowest rate of skin test reactivity had a prevalence of allergic rhinitis of 2 percent; those with intermediate reactivity had a prevalence of 53 percent; and those with the highest skin test reactivity had an 89–100 percent prevalence of allergic rhinitis. In a study conducted in Tucson, allergic rhinitis was similar whether skin test reactivity was positive for perennial allergens (such as house dust mites) or seasonal allergens. Nationwide surveys—specifically, the National Health and Nutrition Examination Survey (NHANES)—also relate seasonal rhinitis symptoms to positive skin tests for seasonal allergens (Gergen and Turkeltaub, 1991). A similar relationship was not demonstrated with perennial rhinitis and dust allergy; however, the NHANES was limited because it did not use now-available allergen extracts that allow for improved sensitivity and specificity. Allergic rhinitis was independently associated with allergy to rye grass, ragweed, and house dust. Another nationwide survey is in progress using additional allergens.

A study in six U.S. cities (Brunekreef et al., 1989) found significant relationships between rates of hay fever and "mold" or "dampness" in homes (odds ratios of 1.57 and 1.26, respectively), although neither finding could be correlated with fungal counts (Su et al., 1989; 1990).

Age The prevalence of allergic rhinitis increases with age, up to the middle years, and then decreases. This same age-related pattern has been seen in studies with widely varying prevalence rates. For children, the National Health Interview Survey (NHIS) developed a prevalence rate of allergic rhinitis without asthma of 5.3 percent for those under age 18. A community-based study of non-Hispanic Caucasians in Tucson showed a prevalence of allergic rhinitis of 29.4 percent in children ages 3–14 (Lebowitz et al., 1975). Rates in other studies have been reported as between 3 and 19 percent (Arbeiter, 1967; Broder et al., 1962; Freeman and Johnson, 1964; Smith and Knowles, 1965). For adults, the NHIS study elicited a rate of 11.2 percent for ages 18–44, whereas the Tucson study found a prevalence of 42.6 percent in those over age 15. This rate was thought to be due in part to the migration of allergic subjects to Tucson. The NHIS study showed a prevalence of 9 percent for ages 45–64 and 5.2 percent for ages 65 and older (NCHS, 1986).

ECZEMA

Eczema (eczematous dermatitis) is a characteristic inflammatory response of the skin to multiple stimuli. There is usually a primary elicitor of the response (such as an allergen) after which many factors may contribute. The unifying feature of eczematous dermatitis is the occurrence of vesicular



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