The relationship between influenza outbreaks and acute ischemic heart disease in Maryland residents over a 7-year period.

BACKGROUND: We sought to expand the understanding of relationships of influenza outbreaks to ischemic heart disease (IHD)-related events.
METHODS: Retrospective data sources were used to examine relationships of intense influenza outbreak periods (intense-IOP) to rates of IHD-related hospitalizations and deaths for Maryland residents aged ≥ 50 years. Rate ratios (RRs) were calculated for medical outcomes during intense-IOP compared to non-IOP for 7 years.
RESULTS: RRs for IHD-related hospitalizations (RR=1.06), deaths (RR=1.16), and combined hospitalizations for IHD- and medically attended acute respiratory illness (MAARI) (RR=1.42) were significantly elevated during intense-IOP over the 7 years (P< .01). RRs for IHD-related hospitalizations increased significantly with age (P= .0007). Also, RRs for IHD-related hospitalizations each year were significantly correlated to proportions of circulating A/H3N2 viruses in that year (correlation coefficient [CC] =0.83, P= .02). Finally, for residents aged ≥ 65 years, RRs for IHD-related hospitalizations each year were significantly correlated with magnitude of the intense-IOPs in that year as measured by RRs for MAARI-related emergency department (ED) visits (CC=0.77, P= .04).
CONCLUSIONS: These data suggest that influenza infections, particularly by A/H3N2 viruses, are directly associated with acute IHD-related events in older individuals.