Relationship between seasonal influenza rates and hospitalization and mortality rates due to acute cardiovascular diseases in a Spanish region.

Introduction And Objective: Influenza virus infection can contribute to cardiovascular morbidity and mortality. The purpose of this study is to confirm if the increase in seasonal influenza rates is associated with a growth in hospitalisation and mortality rates for acute cardiovascular diseases (ACVD).

Methods: Retrospective cohort study of hospital discharges due to ACVD (myocardial infarction, unstable angina, heart failure and ischemic stroke) in the Castilla y León (Spain) hospital system between 2001 and 2015. Hospitalisation and hospital mortality rates due to ACVD, and influenza rates in Castilla y León between 2001 and 2015 were studied. To calculate hospitalisation and mortality rates, the hospital discharges database was used; for influenza rates, the weekly reports of the Sentinel System for the surveillance of influenza in Spain (Carlos III Health Institute) were used. A statistical analysis of linear and multivariate logistic regressions was performed.

Results: 239,586 ACVD (myocardial infarction: 55,004; unstable angina: 15,406; heart failure: 11,1647; ischemic stroke: 57,529) were studied. Increasing rates of influenza were associated with increased mortality due to ACVD and all the diseases studied, except unstable angina. A linear correlation was observed between influenza rates and hospitalisation (r=0.03; p=0.02) and mortality (r=0.14; p<0.001) rates by ACVD. Virtually all influenza rates were associated, as independent variables, to an increase in mortality due to ACVD, being higher in rates>139/100,000 inhabitants (OR: 1.25; p<0.001).

Conclusions: The rates of hospitalisation and in-hospital mortality due to ACVD in the period 2001-2015 increased in relation to infection rates due to the influenza virus.