Higher Rates of MI Following Influenza Infection

Published - Written by Rachel Wolfson, M.D., Ph.D.

Mr. Williams is a 71-year-old patient with a history of coronary artery disease, hypertension, and hyperlipidemia. He presents to your office in the fall for his annual physical exam and says that he would prefer not to get the flu vaccine this year because he doesn’t think he is at high risk of getting the flu. After counseling him about the importance of vaccination for reducing the spread of infection, he asks if there are any other benefits of the vaccine. A retrospective study by Kwong et al. in this week’s NEJM sheds some light on this question. 

The authors analyzed the number of hospitalizations for acute myocardial infarctions (MI) that occurred during the week after a positive influenza test (risk interval) and 1 year before and after the risk interval (control interval). Of 364 MIs that occurred during the year before and after positive influenza testing, 20 admissions occurred during the 1-week risk interval and 344 occurred during the control interval (20 vs. 3.3 admissions per week). This translates to an incidence ratio of 6.06, indicating that the likelihood of an admission for MI during the week after a positive influenza test was six times higher than during the control interval. The incidence ratio of acute MI was also higher after infection with respiratory syncytial virus (RSV; incidence ratio, 3.51), respiratory virus other than RSV and influenza (2.77), and respiratory illnesses in which no respiratory virus was identified (incidence ratio, 3.30). The authors hypothesize that the viral illness increases acute inflammation, biochemical stress, and vasoconstriction that, in the setting of atherosclerotic vascular disease, can lead to an increased risk of MI.

These results have many interesting implications. First, the association between respiratory virus infection and MI further emphasizes the importance of vaccinating patients for the flu virus each year, especially those at high risk for adverse cardiovascular events, such as Mr. Williams. In addition, these data imply that we should have a higher suspicion for myocardial events during the week after a respiratory infection and that the diagnosis of MI should be sought and ruled out in the appropriate clinical scenario. Finally, future work is needed to examine whether any early interventions for respiratory infections can mitigate the risk of subsequent MI.

Knowing the association between influenza and increased risk for MI during the week after infection could be the last push that Mr. Williams needs to get the flu vaccine this year.

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Rachel is a fifth-year MD/PhD student at Harvard Medical School. She is originally from Okemos, MI, and graduated from Stanford University in 2011. For her PhD research, she is studying the regulation of cell growth in response to nutrients.