Seasonal Influenza Infections and Cardiovascular Disease Mortality

Abstract

Importance: Cardiovascular deaths and influenza epidemics peak during winter in temperate regions.

Objectives: To quantify the temporal association between population increases in seasonal influenza infections and mortality due to cardiovascular causes and to test if influenza incidence indicators are predictive of cardiovascular mortality during the influenza season.

Design, setting, and participants: Time-series analysis of vital statistics records and emergency department visits in New York City, among cardiovascular deaths that occurred during influenza seasons between January 1, 2006, and December 31, 2012. The 2009 novel influenza A(H1N1) pandemic period was excluded from temporal analyses.

Exposures: Emergency department visits for influenza-like illness, grouped by age (≥0 years and ≥65 years) and scaled by laboratory surveillance data for viral types and subtypes, in the previous 28 days.

Main outcomes and measures: Mortality due to cardiovascular disease, ischemic heart disease, and myocardial infarction.

Results: Among adults 65 years and older, who accounted for 83.0% (73 363 deaths) of nonpandemic cardiovascular mortality during influenza seasons, seasonal average influenza incidence was correlated year to year with excess cardiovascular mortality (Pearson correlation coefficients ≥0.75, P ≤ .05 for 4 different influenza indicators). In daily time-series analyses using 4 different influenza metrics, interquartile range increases in influenza incidence during the previous 21 days were associated with an increase between 2.3% (95% CI, 0.7%-3.9%) and 6.3% (95% CI, 3.7%-8.9%) for cardiovascular disease mortality and between 2.4% (95% CI, 1.1%-3.6%) and 6.9% (95% CI, 4.0%-9.9%) for ischemic heart disease mortality among adults 65 years and older. The associations were most acute and strongest for myocardial infarction mortality, with each interquartile range increase in influenza incidence during the previous 14 days associated with mortality increases between 5.8% (95% CI, 2.5%-9.1%) and 13.1% (95% CI, 5.3%-20.9%). Out-of-sample prediction of cardiovascular mortality among adults 65 years and older during the 2009-2010 influenza season yielded average estimates with 94.0% accuracy using 4 different influenza metrics.

Conclusions and relevance: Emergency department visits for influenza-like illness were associated with and predictive of cardiovascular disease mortality. Retrospective estimation of influenza-attributable cardiovascular mortality burden combined with accurate and reliable influenza forecasts could predict the timing and burden of seasonal increases in cardiovascular mortality.

Figure 1. Time Series of Daily Cardiovascular Disease (CVD) Mortality and the Percentage of Emergency Department Visits for Influenza-Like Illness (ILI) and ILI+ in New York City, 2006 to 2012

ILI+ is a scaled measure of ILI that incorporates laboratory surveillance data. Noninfluenza seasons (weeks 21–39 in a calendar year, indicated by gray shading) and the 2009 novel influenza A(H1N1) pandemic were excluded from temporal analyses in this study.

Figure 2. Scatterplot Comparing Seasonal Excess Cardiovascular Disease (CVD) Mortality With Seasonal Average Emergency Department Visits for Influenza-Like Illness (ILI) in New York City, 2006 to 2012

The 2005–2006 season includes only weeks 1 to 20 of calendar year 2006, and the 2012–2013 season includes only weeks 40 to 52 of calendar year 2012. Excluding the 2009–2010 influenza season (hollow symbols), r = 0.75 (P = .05) for adults 65 years and older and r = 0.59 (P = .16) for adults younger than 65 years.

Figure 3. Percentage Change in Daily Mortality From Cardiovascular Disease (CVD), Ischemic Heart Disease (IHD), and Myocardial Infarction (MI) per Interquartile Range (IQR) Increase in an Influenza Infection Measure

Influenza-like illness (ILI), total and for age 65 years and older, represents the number of emergency department visits for ILI among persons 0 years and older and 65 years and older, respectively, while ILI+ measures additionally incorporate virologic surveillance data into the metric.