ACUTE RESPIRATORY-TRACT INFECTIONS AND RISK OF FIRST-TIME ACUTE MYOCARDIAL-INFARCTION

Background. There is growing interest in the role of infections in the aetiology of acute myocardial infarction (AMI). We undertook a large, population-based study to explore the association between risk of AMI and recent acute respiratory-tract infection. Methods We used data fr om general practices in the UK (General Practice Research Database). P otential cases were people aged 75 years or younger, with no history o f clinical risk factors, who had a first-time diagnosis of AMI between Jan 1, 1994, and Oct 31, 1996. Four controls were matched to each cas e on age, sex, and the practice attended. The date of the AMI in the c ase was defined as the index date. For both cases and controls the dat e of the last respiratory-tract infection before the index date was id entified. We also did a case-crossover analysis of cases who had an ac ute respiratory-tract infection either before the index date or before an arbitrarily chosen date (1 year before AMI). Findings. In the case -control analysis of 1922 cases and 7649 matched controls, significant ly more cases than controls had an acute respiratory-tract infection i n the 10 days before the index date (54 [2.8%] vs 72 [0.9%]). The odds ratios, adjusted for smoking and body-mass index, for first-time AMI in association with an acute respiratory-tract infection 1-5, 6-10, 11 -15, or 16-30 days before the index date (compared with participants w ho had no such infection during the preceding year) were 3.6 (95% CI 2 .2-5.7), 2.3 (1.3-4.2), 1.8 (1.0-3.3), and 1.0 (0.7-1.6); (test for tr end p < 0.01). The case-crossover analysis showed a relative risk of 2 .7 (1.6-4.7) for AMI in relation to an acute respiratory-tract infecti on in the 10 days before the index date. Interpretation. Our findings suggest that in people without a history of clinical risk factors for AMI, acute respiratory-tract infections are associated with an increas ed risk of AMI for a period of about 2 weeks. We cannot, however, comp letely exclude the possibility of misdiagnosis bias, if prodromal symp toms oi AMI were mistaken for respiratory-tract infection.