The Spanish influenza pandemic in occidental Europe (1918–1920) and victim age

BACKGROUND Studies of the Spanish Influenza pandemic (1918-1920) provide interesting information that may improve our preparation for present and future influenza pandemic threats. METHODS We studied archives from France, Italy, Spain and Portugal, obtaining high-quality data that allowed us to calculate mortality rates associated with the Spanish flu and to characterize the proportional distribution of influenza deaths by age in the capital cities of these countries. RESULTS French and American troops who fought in the First World War began to be affected from April 1918 onwards by a benign influenza epidemic, which hardly caused any deaths. The first occidental European country in which the pandemic spread to large sectors of the population, causing serious mortality, was Spain. The associated influenza provoked in Madrid a mortality rate of 1.31 per 1000 inhabitants between May and June (1918). In the following months of June and July, the epidemic spread to Portugal, but did not reach the Pyrenees. In September 1918, the influenza pandemic spread with tremendous virulence, presenting itself simultaneously during the month of October in South Western European countries. In Madrid, the 1918 excess mortality due in large part to the influenza pandemic is estimated at 5.27 per 1000. In Paris, the 1918 mortality rate provoked by the influenza and pathologies of the respiratory system was 6.08 per 1000. In South Western European countries, mortality rates oscillated between 10.6 and 12.1 per 1000 inhabitants. A study of the age distribution of deaths due to influenza between 1916 and 1921 reveals that the Spanish influenza principally affected men and women between 15 and 44 years of age. Deaths associated with the seasonal influenza of 1916, 1917 and 1921 represented 19.7%, 12.5% and 21.0% of all deaths respectively, whereas during the rawest moments of the Spanish influenza, in 1918, the proportion of deaths due to flu for those aged between 15 and 44 years of age reached 68.2% in Paris and 66.3% in Madrid. CONCLUSION Victim age is an important criterion that can be used to evaluate the phase and evolution of pandemic influenza. The Spanish Influenza affected particularly the 25- to 34-year-old and 15- to 24-year-old age groups.