Although the “infectious” hypothesis for acute coronary syndrome has not been borne out in clinical trials (antimicrobial therapies have failed) there is abundant epidemiological evidence that influenza infection may contribute to increases in cardiovascular hospitalizations and rates of acute myocardial infarction (MI).
For this reason, authors of a recent case-control study published in the British Medical Journal investigated whether influenza was a significant and unrecognized precipitant of acute MI. In this study, patients were 40 years or older with acute MI (AMI), evolving, or recent AMI who were admitted to a tertiary referral center during influenza season in Sydney, Australia, from 2008 to 2010; controls were outpatients without a diagnosis of AMI during the same period. There were 559 participants in the study and half had received vaccination against flu. There was a 2-fold increase in the OR for influenza infection for AMI patients vs those without MI; however, this association was rendered non-significant after adjustment and influenza infection was no longer a predictor of MI. Interestingly, however, although vaccination was underutilized, being vaccinated was nevertheless associated with a significantly lower rate of AMI compared with non-vaccination (OR = 0.55; 95% CI, 0.35-0.85).
The authors point out that the potential public health impact of influenza vaccination, particularly among adults aged 50 to 64 years—a group at risk for AMI but not targeted for vaccination—should be explored further. For the primary care practitioner, the study results provide yet another reason to encourage patients to receieve influenza vaccination—AMI prevention.
MacIntyre CR, Heywood AE, Kovoor P, et al. Ischaemic heart disease, influenza and influenza vaccination: a prospective case control study. Heart Online First, August 21, 2013. doi:10.1136/heartjnl-2013-304320 (Full text)