This article has documented the wide international variation in asthma mortality rates in people aged five to 34 years over the last 15 years. New Zealand is the only country to have experienced a major epidemic in this period, although reported asthma mortality rates have been increasing in recent years in most other countries examined. The data were based on statistical coding of information on death certificates, but only in three countries (New Zealand, United States, and United Kingdom) had the validity of these data been examined. The age group five to 34 was chosen to maximize the validity of the data. In this age group, it has been shown that false positive death certificates are exceedingly rare in both New Zealand and the United Kingdom; false negatives were also found to be rare in one small New Zealand study. more
The change from the eighth to the ninth revision of the ICD in 1979 had little affect on asthma mortality rates in the five- to 34-year old age group. In the eighth revision, asthma with mention of bronchitis was coded as bronchitis, whereas under the ninth revision, it was coded as asthma unspecified. In New Zealanders aged five to 34 years, the maximum possible increase that could be attributed to the change in selection rules in 1979 was calculated as approximately 5 percent. When cases included in the 1981 to 1983 New Zealand National Asthma Mortality Study were coded under both the eighth and ninth revisions of the ICD, the difference in coded deaths in five- to 34-year-old subjects was only 2.4 percent (unpublished data). A bridge coding exercise undertaken on a sample of asthma deaths in the United Kingdom in 1979 indicated that the increase in asthma mortality which could be attributed to the ICD revision in five- to 34-year-olds was only 6 percent The finding that recent increases in asthma mortality in England and Wales and the United States coincided with a decline in deaths from other respiratory diseases raised the possibility that there may have been a shift in the classification of respiratory deaths in these countries.