S18 Investigating the impact of influenza activity on excess mortality rates from cardiovascular, respiratory and renal diseases in Ireland during the 2010/11–2019/20 influenza seasons

IntroductionCOVID-19 and influenza infection are associated with cardiovascular, respiratory and renal complications. However, cardiovascular, respiratory and renal disease mortality rates in Ireland decreased by 0.04%, 0.12% and 0.12% respectively in 2020 relative to 2019, despite nearly 100,000 new COVID-19 cases being reported in Ireland in 2020. Government-imposed social distancing measures resulted in abolition of influenza activity (IA). We analysed population data from the 2010/11–2019/20 influenza seasons to estimate the impact of reduced IA on cardiovascular, respiratory and renal disease mortality rates during the COVID-19 pandemic season.MethodsQuarterly mortality data for acute myocardial infarction (AMI), cerebrovascular disease, pneumonia, asthma and renal disease from first quarter (Q1) 2010 to fourth quarter (Q4) 2020 was obtained from the Central Statistics Office. Weekly data on influenza-like illness (ILI) rates and positive percentages (PP) (i.e., proportion of influenza-positive sentinel respiratory specimens) was obtained from the Health Protection Surveillance Centre. Excess mortality rate during influenza season was defined as the percentage difference between Q4/Q1 and preceding third quarter (Q3) mortality rates. We adopted the Goldstein Index (ILI rate × PP) as an indicator of IA. Time series analyses, Pearson correlation coefficients (r) and linear regression models were used to evaluate the relationships between IA and excess cardiovascular, respiratory and renal disease mortality rates.ResultsStatistically significant positive associations were observed between IA and excess AMI (r=0.557, p=0.011), cerebrovascular disease (r=0.858, p<0.001), pneumonia (r=0.635, p=0.003), asthma (r=0.668, p=0.001) and renal disease (r=0.652, p=0.002) mortality rates. Linear regression models predicted 0.072% (95% confidence interval 0.019%, 0.125%), 0.095% (0.067%, 0.123%), 0.184% (0.073%, 0.296%), 0.367% (0.165%, 0.569%) and 0.124% (0.053%, 0.196%) increases in excess AMI, cerebrovascular disease, pneumonia, asthma and renal disease mortality rates respectively per unit increase in IA.ConclusionElimination of IA may have contributed towards limiting the effects of COVID-19 on cardiovascular, respiratory and renal disease mortality rates in Ireland.