Printed In Great Britain Impact of Influenza on Mortality in Relation to Age and Underlying Disease, 1967-1989

estimated for a 22.5-year period (1967-1989) in four age groups and three entities of disease, using Poisson regression techniques. Our analysis suggests that, on average, more than 2000 people died from influenza in The Netherlands each year, but in only a fraction of these deaths was influenza recognized as the cause of death. For each case of death registered as caused by influenza (registered influenza mortality), 2.6 additional cases of death registered as due to causes other than influenza, nevertheless, were influenza-related (non-registered influenza mortality). Therefore, the overall impact of influenza on mortality is estimated to be greater than registered influenza mortality by a factor of 3.6. Those under 60 years of age accounted for 5 % of all non-registered influenza deaths, whereas people aged 60-69, 70-79 years and>80 years accounted for 12%, 29 % and 54 % of such deaths, respectively. When extrapolating the figures for the Dutch population of 1989, we could attribute, on average per season-year, 82 deaths per 100000 people>60 years, 143 In people>70 years, and 280 in people>80 years. Of all non-registered influenza cases of death, 47% were estimated to occur in people with heart disease as a primarily reported cause of death, 23 % in those with lung disease, and 30 % in those with other diseases. This study stresses the serious effects of influenza, mainly in the elderly (95 % of non-registered influenza mortality). Prophylactic measures (vaccination) should not only be stimulated among populations with defined underlying diseases, but generally among all people-"60 years. Future research should address the pathological mechanisms which lead to influenza-related excess mortality