SOURCE: Kwong JC, et al. N Engl J Med 2018;378:345-353.

It is obvious that influenza is an important cause of morbidity and mortality. Exploration of the causes of death related to influenza is a bit more complicated. Reporting on influenza epidemics usually includes the single broad category “influenza and pneumonia,” since that category tracks directly with incident cases of influenza each year.

But even with that clarification, the proportion of patients who succumb to influenza pneumonia vs. those who incur bacterial pneumonia (typically Staph) subsequent to pneumonia vs. all other incident pneumonias that occur concomitantly with flu season is not readily discernible. The association between cardiovascular event rates and influenza has been recognized since the 1930s, but few direct studies of rates of myocardial infarction in patients with acute influenza have been performed. To that end, Kwong et al reported that in a study of subjects with laboratory-confirmed influenza (n = 19,045), myocardial infarction rates were six-fold higher in the “risk interval” (i.e., seven days after influenza identification) than in the “control interval” (i.e., one year immediately before and after the risk interval). Although other viral infections, such as respiratory syncytial virus, also were associated with increased risk for myocardial infarction, of the viruses studied, influenza incurred the greatest relative risk increase.