Background: Reports of an increase in asthma-related mortality have been based on studies of death certificates from the general U.S. population on which asthma was listed as an underlying cause of death. We addressed the issue in a different way by analyzing long-term survival in a defined, population-based cohort of patients with asthma.
Methods: We identified all residents of Rochester, Minnesota, in whom asthma was diagnosed from January 1, 1964, through December 31, 1983, by reviewing the medical records of all patients with asthma and associated diagnoses, using explicit predefined criteria. The patients' vital status at last follow-up was ascertained. Medical records, death certificates, and autopsy reports were reviewed to classify deaths as due either to asthma or to other conditions.
Results: We identified 2499 patients with definite or probable asthma. The mean duration of follow-up was 14 years (range, 0 to 29). There were 140 deaths during 32,605 person-years of follow-up. Overall survival was not significantly different from the survival that was expected for residents of Rochester. Survival was less than expected in patients who were 35 years of age or older when their asthma was diagnosed and who also had another lung disease (predominantly chronic obstructive pulmonary disease). Four percent of all deaths in the study cohort were due to asthma, and all were among adults. Survival was not related to the year of onset of asthma.
Conclusions: Survival among patients with asthma but no other lung disease was not significantly different from expected survival. However, patients 35 or older who had asthma associated with chronic obstructive pulmonary disease did have worse than expected survival. Asthma was classified as the cause of death in only 4 percent of the patients, and there was no evidence of an increased risk of death among patients with a more recent diagnosis of asthma. These results provide assurance that community-based patients with asthma usually have a good prognosis.