FIGURE 2-6 Effect of case definition on estimates of the prevalence of asthma. Shaded area indicates the range of data. Sources: Barbee et al., 1985; Britton et al., 1986; Peat et al., 1987.

rate of about 0.5 percent (Barbee et al., 1985). Over the past 20 years, much higher current and cumulative prevalence rates have been reported from surveys of both children and adults; Figure 2-7 shows the rise in rates for 1980–1987 alone. Mortality epidemics occurred in Britain and Australasia around 1960 and in Britain and New Zealand in the 1970s. U.S. surveys in the 1970s showed prevalence rates of between 4 and 6.7 percent (Barbee et al., 1985; NCHS, 1986). In 1983 Sharma and Balchum stated that 9 million Americans had asthma, 3 million of whom were children.

Recent data also suggest a possible increase in the severity of asthma, using mortality and hospitalization rates as indices of severity (Figures 2-8 and 2-9, respectively; Barbee et al., 1985; Gergen and Weiss, 1992; Gregg, 1983, 1989). Hospital admissions appear to have increased remarkably in Great Britain and the United States, paralleling the increase in prevalence. The hospital discharge rate with asthma as the first-listed diagnosis rose 43 percent among children less than age 15 from 19.8 to 28.4 discharges per 10,000 population (NHLBI, 1991). A 5 percent increase in total hospitalizations for asthma occurred between 1987 and 1990 (NCHS, 1992). These data could reflect changes in the course of the disease or changes in medical



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