In the latest study to link influenza and cardiovascular disease, researchers found that the most severe flu seasons coincided with spikes in hospitalizations for heart failure.
“While several previous studies examining the association between influenza and CV disease have focused on mortality, fewer have explored the extent to which influenza contributes to CV hospitalizations specifically due to heart failure (HF),” Sonja Kytomaa, MPH, with Brigham and Women’s Hospital in Boston, and colleagues wrote in JAMA Cardiology. “Patients with or at risk for HF are thought to be especially vulnerable to influenza-associated complications because of some degree of immunocompromise and have been shown to mount less vigorous responses to influenza vaccines.”
To test this theory, Kytomaa et al. analyzed the association between flu activity and hospitalizations for heart failure and myocardial infarction (MI) in the four U.S. communities which enrolled patients in the Atherosclerosis Risk in Communities (ARIC) study. These trends were tracked from October 2010 to September 2014.
Monthly influenza-like illness (ILI) activity was defined as the percentage of patient visits for ILI—fever, cough or sore throat without a known cause—in those communities as reported by the CDC’s U.S. Outpatient Influenza-Like Illness Survey Network. Other CDC-reported measures such as influenza-associated hospitalizations and deaths due to pneumonia and the flu also factored into determining the severity of each region’s flu season.
Overall, the authors determined that every 5 percent increase in monthly flu activity was associated with a 24 percent increase in heart failure hospitalization rates. This relationship was calculation after adjustments for each community’s total population, its region and the season, as well as race/ethnicity, sex, age and number of heart failure hospitalizations from the month before.
The other half of the authors’ hypothesis, however, wasn’t reflected in the data. Although there was a trend toward an increase in MI hospitalizations with more flu activity, the association wasn’t statistically significant.
“The lack of a clear association in our analysis is likely a function of power and insufficient temporal resolution to detect the association between influenza infection and MI,” Kytomaa and co-authors wrote. “In addition, the population sampled for MI in ARIC surveillance is younger than that sampled for HF hospitalizations and thus may be less likely to manifest the association.”
Kytomaa et al. collected data from more than 450,000 adults for their analysis, including 3,541 MI hospitalizations and 4,321 heart failure hospitalizations. They said the mechanism connecting the flu to cardiovascular events isn’t proven, but they offered a few potential contributors.
“Influenza increases metabolic demand and, in the setting of hypoxemia, may exacerbate underlying cardiac conditions,” the researchers wrote. “Patients with HF have limited cardiac and respiratory reserves and are unlikely to tolerate infection-associated cardiac compromise.”
The link between the flu and heart failure hospitalizations was noted across age groups and in urban, suburban and rural communities, potentially making the findings more generalizable than previous reports—which focused more on elderly populations—would suggest.
“Addressing influenza activity may be valuable in efforts to prevent HF hospitalizations,” Kytomaa et al. wrote. “Further studies are necessary to determine whether strategies to reduce influenza activity at the population level reduce the incidence of MI and HF hospitalizations.”
Daniel joined TriMed’s Chicago editorial team in 2017 as a Cardiovascular Business writer. He previously worked as a writer for daily newspapers in North Dakota and Indiana.