Putting spain back in spanish influenza: quantifying the timing and mortality impact in madrid of the 1918-1921 pandemic through spatial, demographic, and social lenses
- Autores: Laura Cilek
- Directores de la Tesis: Diego Ramiro Fariñas (dir. tes.), Gerardo Chowell (codir. tes.), Albert Esteve Palós (tut. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2019
- Idioma: español
- Materias:
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- Resumen
Just over one hundred years ago, a series of epidemic influenza outbreaks swept through the world. Dubbed the “Spanish flu,” the entirety of these outbreaks contributed to millions of excess deaths in less than one year. While research has long been focused on several aspects of the pandemic, not limited to its virology, aspects of its morbidity and mortality impact, and social and spatial variation in its manifestation, questions remain unanswered. This dissertation attempts to address several unresolved questions persist today using newly digitized data sources, primarily the Madrid Civil Register death records from 1917-1922. As a body of work, the following chapters contextualize Madrid’s experience of Spanish flu to both the rest of Spain and other parts of the world. Better understanding of these historical issues can help contemporary epidemiologists and policy makers to better prepare for future outbreaks. A discussion of the broad themes noted below are woven through the totality of the work.
Timing and strength of individual and successive waves:
During the strong fall wave in Spain, is a geographic pattern of transmission visible? In line with previous assessments of the spread of influenza in Spain in 1918, a clear pattern of movement from the northeast to the west and south was statistically found using sequence analysis. Rural areas appear to have a stronger (higher R) and longer lasting fall wave than the provincial capital cities. However, within the urban center of Madrid, while variation in timing and strength existed, any geographic pattern is difficult to ascertain.
What is the impact of successive waves in a population? In the case of Spain, cities and provinces known to have a herald wave in spring or summer 1918 appear to experience fall waves of lower Reproduction numbers than those areas in which a herald wave is not known to have occurred. Madrid was hit with a particularly strong herald wave, and the excess mortality in the city is lower relative to other large urban areas, especially in the fall wave. With regards to cause of death, it appears that earlier waveswere particularly deadly to those with pre-existing diseases, such as tuberculosis. These first outbreaks effectively harvested these deaths, which did not occur in later waves.
Age-specific mortality patterns:
How much excess mortality occurred in each wave, and to what extent did excess mortality peak in young adult ages? Calculated as the amount of observed mortality above the expected level, age-specific excess mortality patterns during the outbreak are known to have varied across the world, but often a particular pattern is visible of increased mortality excess in young-adult ages. In the city of Madrid, this pattern is less prominent than in other locations in the world, such as Scotland, but there is a small localized peak in absolute excess mortality during the fall-winter 1918-19 wave. Relative excess mortality is found to be the highest in young adults in all waves. Given the presence of a strong herald wave in Madrid, the extent to which a protective effect of earlier exposure may have tempered the amount of mortality and prevalence of a young adult mortality spike is unknown. In an echo wave in both Madrid (1919-20) and Scotland (1920-21), the youngest and oldest are most affected, implying both a return to seasonal influenza mortality patterns and a lack of immunity among the youngest children, conceived and born after the outbreaks.
Mortality risk from a neighborhood perspective:
How did demographic, social, and spatial variation contribute to increased mortality? At the time of the outbreaks, Madrid was a very heterogeneous city, consisting of the richest rich and poorest poor. Some neighborhoods consisted of similar groups of people, while others were incredibly diverse. This makes the analysis of an area’s traits with respect to excess mortality difficult. Nonetheless, the dissertation clearly finds that irrespective of other social and constructed characteristics, such as social class, literacy level, and population density, the amount of baseline mortality in an area is the best predictor of excess mortality during the outbreaks. That is to say, those areas with the highest rates of pre-pandemic mortality also faced devastating losses of life during each pandemic wave. This adds to other evidence in the dissertation that suggests those most vulnerable before the influenza epidemic continued to experience higher levels of mortality during the outbreaks.
