Death Patterns during the 1918 Influenza Pandemic in Chile - Volume 20, Number 11—November 2014 - Emerging Infectious Disease journal - CDC

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Death Patterns during the 1918 Influenza Pandemic in Chile - Volume 20, Number 11—November 2014 - Emerging Infectious Disease journal - CDC

Volume 20, Number 11—November 2014

Research

Death Patterns during the 1918 Influenza Pandemic in Chile

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• Material and Methods
• Results
• Discussion
• Suggested Citation

Figures

• Figure 1
• Figure 2
• Figure 3
• Figure 4
• Figure 5
• Figure 6

Tables

• Table 1
• Table 2

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Gerardo Chowell , Lone Simonsen, Jose Flores, Mark A. Miller, and Cécile Viboud

Author affiliations: Arizona State University, Tempe, Arizona, USA (G. Chowell); National Institutes of Health, Bethesda, Maryland, USA (G. Chowell, M.A. Miller, C. Viboud); George Washington University, Washington, DC, USA (L. Simonsen); University of South Dakota, Vermillion, South Dakota, USA (J. Flores); Universidad de Chile, Santiago, Chile (J. Flores)

Suggested citation for this article

Abstract

Scarce information about the epidemiology of historical influenza pandemics in South America prevents complete understanding of pandemic patterns throughout the continent and across different climatic zones. To fill gaps with regard to spatiotemporal patterns of deaths associated with the 1918 influenza pandemic in Chile, we reviewed archival records. We found evidence that multiple pandemic waves at various times of the year and of varying intensities occurred during 1918–1921 and that influenza-related excess deaths peaked during July–August 1919. Pandemic-associated mortality rates were elevated for all age groups, including for adults >50 years of age; elevation from baseline was highest for young adults. Overall, the rate of excess deaths from the pandemic was estimated at 0.94% in Chile, similar to rates reported elsewhere in Latin America, but rates varied ≈10-fold across provinces. Patterns of death during the pandemic were affected by variation in host-specific susceptibility, population density, baseline death rate, and climate.


The 1918 influenza A(H1N1) pandemic was one of the most devastating epidemic events in recent history; an estimated ≈1% of the global population (20–50 million persons) died (1), including >14 million in India alone (2). Our understanding of the epidemiologic patterns of this pandemic has improved over the past decade as a result of intensive efforts to locate, digitize, and analyze archival disease records (3). In particular, studies focusing on the United States (4,5), Mexico (6), Colombia (7), Brazil (8), and Peru (9) have shed light on geographic variation in the patterns of timing, intensity, and patient age during successive pandemic waves across the Americas. Yet there have been no reports from temperate locales of South America; this gap prevents a complete understanding of the epidemiology of the pandemic throughout the continent and across different climatic zones.

A consistent finding across reports from North America, Europe, Latin America, and Asia (4–7,9–12) is the disproportionate increase in mortality rates among young adults during the pandemic period compared with prepandemic years. Further reports from the United States and Europe have shown that influenza-related deaths among seniors (>50 years of age) were significantly reduced during the lethal 1918–19 pandemic wave relative to baseline periods. In contrast, this protective effect for seniors did not apply to Mexico, Colombia, and remote island populations, probably because of differences in prior immunity between regions (6,13). In addition, large geographic variations in mortality rates from the pandemic have been documented (14–16).

Although recent studies have highlighted latitudinal and climatic variations in contemporary influenza epidemics and pandemics (17–20), little is known about the role of climate in the severity or timing of the 1918 pandemic. Chile is a unique country; it spans an extensive latitudinal gradient, has a variety of climatic zones, and has preserved historical records dating back to the 1918 pandemic period. We characterized geographic variation in pandemic influenza–related death patterns in Chile by using national and regional death statistics combined with a unique dataset of individual-level death certificates from Concepción, a large city in southern Chile. We discuss our findings in relation to those reported elsewhere in the Americas and globally.

Dr Chowell is an associate professor in the School of Human Evolution and Social Change at Arizona State University and Research Fellow at the Fogarty International Center, National Institutes of Health. His research interests include mathematical modeling of infectious disease transmission with a focus on influenza and the role of public health interventions. He is also interested in the quantitative characterization of the 1918 influenza pandemic in the Americas.

Acknowledgment

This research was conducted in the context of the Multinational Influenza Seasonal Mortality Study, an ongoing international collaborative effort to understand influenza epidemiological and evolutionary patterns, led by the Fogarty International Center, National Institutes of Health (http://www.origem.info/misms/index.php). Funding for this project comes in part (L.S.) from the RAPIDD (Research and Policy for Infectious Disease Dynamics) program of the Science & Technology Directorate, Department of Homeland Security, and from the Office of Global Affairs, International Influenza Unit, in the Office of the Secretary of the US Department of Health and Human Services.

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Figures

• Figure 1. The 24 contiguous administrative provinces in Chile in 1918, (A) and location of Chile in South America.
• Figure 2. Temporal evolution (March 1918–December 1921) of all-cause mortality rates during the 1918 influenza pandemic across 24 provinces of Chile, sorted in geographic order from northern to southern Chile. For...
• Figure 3. Excess deaths per 10,000 population across 24 provinces of Chile according to pandemic periods (July 1918–March 1919, June 1919–March 1920, November 1920–March 1921, and June 1921–December 1921) in geographic...
• Figure 4. Relative risk for death over the baseline risk across provinces of Chile according to pandemic periods (July 1918–March 1919, June 1919–March 1920, and June 1921–December 1921). The relative risk...
• Figure 5. Weekly time series of deaths from all causes (A) and respiratory illness (B) per 10,000 population in Concepción, Chile, 1915–1920 (black lines). Shaded areas highlight 3 periods of high...
• Figure 6. Age-stratified weekly respiratory mortality rates in Concepción, Chile, 1915–1920 (black lines). A) <20 years; B) 20–29 years; C) 30–50 years; D) >50 years. Shaded areas highlight 3 periods...

Tables

• Table 1. Estimates of absolute excess mortality rates attributable to pandemic influenza across 24 provinces of Chile, 1918–1921
• Table 2. Estimated rates of absolute excess pandemic deaths, by pandemic wave, age group, and cause of death, Concepción, Chile, 1918–20

Suggested citation for this article: Chowell G, Simonsen L, Flores J, Miller MA, Viboud C. Death patterns during the 1918 influenza pandemic in Chile. Emerg Infect Dis [Internet]. 2014 Nov [date cited]. http://dx.doi.org/10.3201/eid2011.130632

DOI: 10.3201/eid2011.130632