Study Explores Association of Influenza-like Illness and CV Events

A recent study of more than 450,000 has found an association between an increase of influenza activity and an increase in hospitalizations for CV events. Data suggested that in a month with high influenza activity, approximately 19% of hospitalizations for heart failure (HF) could be attributable to influenza.

Investigators sought to explore the temporal association between influenza activity and hospitalization due to heart failure and myocardial infarction (MI), with the hypothesis that increased influenza activity would be associated with increased hospitalizations for these events among adults in the study population. Influenza activity was temporally associated with an increase in HF hospitalizations across 4 influenza seasons. Data suggests that influenza may contribute to the risk of HF hospitalization in the general population.

As part of the community surveillance component of the Atherosclerosis Risk in Communities (ARIC) study, data was collected from annual cross-sectional stratified random samples of hospitalizations of adults between 35 and 84 years of age in 4 US communities. From Oct. 2010 to Sept. 2014, data was collected from Jackson, MI, Minneapolis, MN, Forsyth County, NC, and Washington County, MD. According to the 2010 Census, 451,588 individuals lived in the ARIC communities.

From this, a random sample of eligible hospitalizations were selected based upon 3 criteria: the ICD-9-CM and ICD-10-CM discharge diagnosis codes for hospitalized MI, HF, or HF-associated conditions, age between 35 and 84 years old for MI and 55 or older for HF at time of hospital discharge, and a home address within the boundaries of the ARIC communities. Influenza-like illness (ILI) was defined as a fever, a cough and/or a sore throat, and no known cause of symptoms.

On average, a 5% increase in monthly ILI activity was associated with a 24% increase in HF hospitalization rates within the same month after multivariable adjustment. ILI activity was no significantly associated with MI hospitalization when examined over the 4 seasons. During the 2 most severe influenza seasons, investigators observed a 22% and 20% temporally associated increased risk of HF. Of the seasons studied, peak ILI activity was the highest in the 2012 to 2013 season and the lowest during the 2011 to 2012 season. Consistent with ILI activity, the most pneumonia and influenza-associated deaths occurred during the 2012 to 2013 season (16,451 [27%]) and the lowest number occurred during the 2011 to 2012 season (14,449 [23%]).

Investigators found that the estimated association between ILI activity and hospitalizations for HF and MI overall remained consistent after adjusting for monthly average temperatures. Corresponding risk reduction that was associated with reduced levels of ILI activity suggests that HF hospitalizations were 19% higher in months with elevated ILI activity when compared with a month with baseline ILI activity. No significant reduction in MI hospitalizations was associated with reduced levels of ILI activity.

Data suggests that an increase in population levels of influenza activity is associated with an increase in hospitalizations for CV events. This suggests that addressing this activity may be valuable in efforts to prevent HF hospitalizations. Further studies are needed to determine whether strategies to reduce influenza activity at the population level reduce the incidence of MI and HF hospitalizations.

Investigators noted several limitations within their analysis. Individual influenza illness or vaccination status of those hospitalized for HF or MI was not known. While they associated population-level ILI activity with events, it is possible other infectious causes that might parallel influenza activity might have accounted for some of the associations. Investigators were unable to analyze the association between influenza severity and hospitalizations using other methods, such as the rate of influenza-associated hospitalizations.

The study, “Association of Influenza-like Illness Activity With Hospitalizations for Heart Failure,”is published in the Journal of the American Medical Association.