Years of life lost due to influenza-attributable mortality in older adults in the Netherlands: a competing-risks approach

We estimated the influenza mortality burden in adults aged 60 years or older in the Netherlands in terms of years of life lost, taking into account competing mortality risks. Weekly laboratory surveillance data for influenza and other respiratory pathogens and weekly extreme temperature served as covariates in Poisson regression models fitted to weekly mortality data, specific to age group, for the period 1999-2000 through 2012-2013. Burden for age groups 60-64 years through 85-89 years was computed as years of life lost before age 90 (YLL90), using restricted mean lifetime survival analysis and accounting for competing risks. Influenza-attributable mortality burden was greatest for persons aged 80-84 years, at 914 YLL90 per 100,000 persons (95% uncertainty interval: 867, 963), followed by persons aged 85-89 years (787 YLL90/100,000; 95% uncertainty interval: 741, 834). Ignoring competing mortality risks in the computation of influenza-attributable YLL90 would lead to substantial overestimation of burden, from 3.5% for persons aged 60-64 years to 82% for those aged 80-89 years at death. Failure to account for competing mortality risks has implications for the accuracy of disease-burden estimates, especially among persons aged 80 years or older. Because the mortality burden borne by the elderly is notably high, prevention initiatives may benefit from being redesigned to more effectively prevent infection in the oldest age groups.