Respiratory and circulatory deaths attributable to influenza A & B

Methods Using primary cause of death (Statistics Netherlands) we modeled weekly timeseries of 1) respiratory deaths (ICD10 codes J00-J99) and 2) circulatory deaths (ICD10 codes I00-I99). We used regression models with an identity link and Poisson error to relate mortality to counts of influenza A & B diagnoses. We adjusted for other common respiratory pathogens (all pathogen data was at population level from the national laboratory surveillance), temperature (from the Dutch Royal Meteorological Institute), and baseline linear and cyclical (i.e. seasonal) trends. To account for the yearly variation in the severity of the main circulating influenza A strain we used time dependent variables for influenza A (fixed at lag 0 – assuming a direct effect of influenza. For influenza B and the confoundig pathogens we considered a 0 tot -4 time lag (thus allowing infection to precede death for up to 4 weeks). We performed the analyses separately per death cause group and by 3 different age groups (0-64, 65-74,75+ years) over a 14-year timeperiod (mid 1999-mid 2013, thus 14 complete winter seasons).