Race and Ethnic Group Several studies have reported racial differences in the prevalence and severity of asthma in the United States, but such results are inconsistent. Schwartz and colleagues (1990) reported an asthma prevalence rate of 7.2 percent among African American children compared with 3 percent among Caucasian children. For adolescents, prevalence is higher among Caucasians (5–6 percent) than among African Americans (3–4 percent); rates for Native Americans are close to zero, and rates among Asians are unknown (Barbee et al., 1985). A study of adults by Di Pede and coworkers (1991) found a prevalence of diagnosed asthma of 4.9 percent among Caucasians (non-Mexican Americans) and a prevalence of 0.9 percent among Mexican Americans. In the same study, Caucasians reported more respiratory symptoms (even within smoking groups) than Mexican Americans. The apparent difference in Caucasian/Mexican American rates may reflect cultural differences in reporting, since the lung function of the two groups is similar for comparable ages, heights, and genders.

Asthma mortality rates are significantly higher among African Americans than among Caucasians (NHLBI, 1991; Sly, 1988). Overall, the death rate from asthma rose from 1.2 per 100,000 population in 1979 to 1.5 in 1983 and 1984. Overall mortality rates among African Americans are two- to threefold higher than among Caucasians and fivefold higher among children. Between 1979 and 1984, the mortality rate rose from 1.8 to 2.5 per 100,000 population among African Americans and from 1.1 to 1.4 per 100,000 among Caucasians.

Socioeconomic Status Socioeconomic status seems to contribute significantly to asthma prevalence rates and to indices of disease severity. Studies have shown that asthma prevalence rates among children are inversely related to socioeconomic status and residential mobility and are directly related to crowding (Lebowitz, 1977, 1989). Schwartz and colleagues (1990) found that both residence in central cities and low income significantly contributed to asthma prevalence rates. Poverty has also been associated with increased hospitalizations for asthma (NHLBI, 1991). A study of inner-city children in the United States demonstrated a cumulative prevalence rate of asthma of 10.6 percent (Mak et al., 1982). (Inner-city asthma death rates in Chicago were two times greater than those for the United States; in New York City they were three times greater than those for the United States [Evans, 1992; K. B. Weiss et al., 1992a].) The criterion for diagnosis in that study was a positive response to the following question: Have you ever had a condition that causes difficulty in breathing, with wheezing noises in the chest?

Air Pollution Recent human challenge studies showed a twofold increased sensitivity to allergen in allergic asthmatics following a 1-hour exposure to ozone under conditions typical of summer smog (0.12 parts per

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