[Premature mortality excess related to influenza in Spain during an interpandemic period]

The indicator of Potential Years of Life Lost (PYLL) has been frequently used to analysis of premature mortality and recently has been used to estimate the impact of the last influenza A(H1N1)pdm09 pandemic. The aim of this study was to estimate the excess deaths from pneumonia and influenza (P&I) in Spain and the PYLL during the period 1980-2008, measuring the mortality attributable to influenza regarding the type/subtype of influenza dominant in each season.

Monthly excess deaths were calculated with cyclical regression models. The PYLL calculation was performed as the product of the number of excess deaths and the difference between life expectancy at birth and years lived for each age group. The analysis of the variation between P&I excess deaths and PYLL, depending on the predominant influenza virus type/subtype was carried out with a Poisson regression analysis.

In seasons dominated by influenza virus A(H3) the average P&I excess deaths was estimated at 1,348, and for PYLL in 5.297, while in seasons dominated by A(H1) or B the average P&I excess deaths was 648, and for PYLL 2.885. The adjusted rate ratios of excess (2.11, CI-95%=2.05-2.16) and PYLL (1.86, CI-95%=1.83-1.88) indicate that the relative frequencies for both indicators are significantly larger in seasons dominated by influenza virus A(H3).

Excess deaths and PYLL doubled when comparing seasons predominantly subtype A(H3) and other influenza viruses.