Background: Experimental and epidemiological studies show a positive association between coronary disease and various infections in different organs, both viral and bacterial and both acute and chronic. Most attention has been paid to dental infections and infections in the respiratory tract. We have studied how chronic respiratory infection predicts coronary disease.
Methods: We defined chronic respiratory infection by the occurrence of symptoms of chronic bronchitis. We also analysed whether any association with coronary disease incidence and mortality is independent of the known major cardiovascular risk factors and whether it is similar among persons in different occupations. Our cohort study was a 13-year follow-up of 19,444 randomly selected eastern Finnish men and women born between 1913 and 1947 and examined in either 1972 or 1977.
Findings: During follow-up, there were 1419 first coronary events, either fatal or non-fatal, and 614 coronary deaths. Among men, the age-adjusted and study-year-adjusted risk ratio of long lasting-symptoms of chronic bronchitis (during as much as 3 months in a year) was 1.52 (95% CI 1.33-1.75) for coronary disease and 1.74 (CI 1.43-2.11) for coronary death. Among women the risk ratios were 1.38 (1.07-1.78) and 1.49 (0.98-2.27), respectively. Inclusion of smoking, serum cholesterol, and systolic blood pressure into the models decreased risk ratios to 1.36 (1.17-1.56) and 1.55 (1.26-1.90) in men and to 1.34 (1.04-1.74) and 1.41 (0.92-2.16) in women, respectively. The risk of coronary disease associated with the symptoms of chronic bronchitis was similar among blue-collar and white-collar workers but the association was not found among farmers.
Interpretation: Symptoms of chronic bronchitis predicted the risk of coronary disease independently from the known major cardiovascular risk factors. If the observed association is causal, prevention and improved management of chronic infections may have played a role in the decrease in coronary disease mortality observed in eastern Finland in the past two decades.