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

Abstract

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.

Figure 1

Age distribution of people who died of influenza in Madrid during 1916. The ordinate represents the absolute number of people who died. The majority of influenza victims were in the +65 years age bracket.

Figure 2

Age distribution of flu victims in Paris during 1917. About 80% of patients were older than 45 years.

Figure 3

Mortality associated with influenza in Paris during 1918. Influenza mortality in Paris began towards the end of September and reaches its climax in the month of October (1918).

Figure 4

Age distribution of influenza‐related deaths during the months of May/June (1918) in Madrid. This mortality profile is clearly different to that associated with a seasonal influenza epidemic (compare with Figure 1). In particular, 52·6% of all influenza‐related deaths were between 15 and 44 years of age, whereas the percentage of deaths in people older than 65 dropped to 12·3%.

Figure 5

Age distribution of influenza deaths in Madrid, during the months October/November (1918). This represents the most intense period of the pandemic. The proportion of influenza deaths for people between the ages of 15–44 rose to 66·3%; for those older than 65 years, the proportion was reduced to 5·9%, whereas for those between the ages of 0 and 4, the proportion was stable at 5·7%.

Figure 6

Age distribution of deaths in Paris during 1918 associated with an influenza diagnosis. It can be seen that the distribution is similar to that of Madrid (Figure 5), indicating the presence of the extremely virulent virus.

Figure 7

Deaths due to influenza in Paris during 1919. The majority of deaths due to influenza occurred between January and March 1919, with over half of the total number of deaths occurring during the month of February.

Figure 8

Age distribution of deaths associated with an influenza diagnosis in Paris in 1919.

Figure 9

Age distribution of deaths due to influenza in Madrid during 1920. The distinct profile signals the final phase of the Spanish influenza pandemic.

Figure 10

Age distribution of deaths due to influenza in Rome, between January and March, 1920; based on data from the 1920 Statistics Bulletin (Bollettino di Statistica del Comune di Roma 1920) that classified deaths into age groups, that are different to those used in other cities, and that does not distinguish male and female deaths.

Figure 11

Age distribution of deaths due to influenza in Madrid 1921. The profile is indicative of seasonal influenza, with a predominance of deaths among older aged people.