The influence of climatic conditions on the transmission dynamics of the 2009 A/H1N1 influenza pandemic in Chile

Gerardo Chowell, Sherry Towers, Cécile Viboud, Rodrigo Fuentes, Viviana Sotomayor, Lone Simonsen, Mark A. Miller, Mauricio Lima, Claudia Villarroel, Monica Chiu, Jose E. Villarroel, Andrea Olea

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Abstract

Background: The role of demographic factors, climatic conditions, school cycles, and connectivity patterns in shaping the spatio-temporal dynamics of pandemic influenza is not clearly understood. Here we analyzed the spatial, age and temporal evolution of the 2009 A/H1N1 influenza pandemic in Chile, a southern hemisphere country covering a long and narrow strip comprising latitudes 17°S to 56°S.Methods: We analyzed the dissemination patterns of the 2009 A/H1N1 pandemic across 15 regions of Chile based on daily hospitalizations for severe acute respiratory disease and laboratory confirmed A/H1N1 influenza infection from 01-May to 31-December, 2009. We explored the association between timing of pandemic onset and peak pandemic activity and several geographical and demographic indicators, school vacations, climatic factors, and international passengers. We also estimated the reproduction number (R) based on the growth rate of the exponential pandemic phase by date of symptoms onset, estimated using maximum likelihood methods.Results: While earlier pandemic onset was associated with larger population size, there was no association with connectivity, demographic, school or climatic factors. In contrast, there was a latitudinal gradient in peak pandemic timing, representing a 16-39-day lag in disease activity from the southern regions relative to the northernmost region (P < 0.001). Geographical differences in latitude of Chilean regions, maximum temperature and specific humidity explained 68.5% of the variability in peak timing (P = 0.01). In addition, there was a decreasing gradient in reproduction number from south to north Chile (P < 0.0001). The regional mean R estimates were 1.6-2.0, 1.3-1.5, and 1.2-1.3 for southern, central and northern regions, respectively, which were not affected by the winter vacation period.Conclusions: There was a lag in the period of most intense 2009 pandemic influenza activity following a South to North traveling pattern across regions of Chile, significantly associated with geographical differences in minimum temperature and specific humidity. The latitudinal gradient in timing of pandemic activity was accompanied by a gradient in reproduction number (P < 0.0001). Intensified surveillance strategies in colder and drier southern regions could lead to earlier detection of pandemic influenza viruses and improved control outcomes.

Original languageEnglish (US)
Article number298
JournalBMC Infectious Diseases
Volume12
DOIs
StatePublished - Nov 13 2012

Fingerprint

Chile
Pandemics
Human Influenza
Reproduction
Demography
Humidity
Temperature
Acute Disease
Population Density
Orthomyxoviridae
Hospitalization

Keywords

  • A/H1N1 influenza pandemic
  • Acute respiratory infection
  • Chile
  • Climatological variables, Specific humidity
  • Influenza-like-illness
  • Reproduction number
  • School cycles
  • Spatial heterogeneity
  • Temperature

ASJC Scopus subject areas

  • Infectious Diseases

Cite this

The influence of climatic conditions on the transmission dynamics of the 2009 A/H1N1 influenza pandemic in Chile. / Chowell, Gerardo; Towers, Sherry; Viboud, Cécile; Fuentes, Rodrigo; Sotomayor, Viviana; Simonsen, Lone; Miller, Mark A.; Lima, Mauricio; Villarroel, Claudia; Chiu, Monica; Villarroel, Jose E.; Olea, Andrea.

In: BMC Infectious Diseases, Vol. 12, 298, 13.11.2012.

Research output: Contribution to journalArticle

Chowell, G, Towers, S, Viboud, C, Fuentes, R, Sotomayor, V, Simonsen, L, Miller, MA, Lima, M, Villarroel, C, Chiu, M, Villarroel, JE & Olea, A 2012, 'The influence of climatic conditions on the transmission dynamics of the 2009 A/H1N1 influenza pandemic in Chile', BMC Infectious Diseases, vol. 12, 298. https://doi.org/10.1186/1471-2334-12-298
Chowell, Gerardo ; Towers, Sherry ; Viboud, Cécile ; Fuentes, Rodrigo ; Sotomayor, Viviana ; Simonsen, Lone ; Miller, Mark A. ; Lima, Mauricio ; Villarroel, Claudia ; Chiu, Monica ; Villarroel, Jose E. ; Olea, Andrea. / The influence of climatic conditions on the transmission dynamics of the 2009 A/H1N1 influenza pandemic in Chile. In: BMC Infectious Diseases. 2012 ; Vol. 12.
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abstract = "Background: The role of demographic factors, climatic conditions, school cycles, and connectivity patterns in shaping the spatio-temporal dynamics of pandemic influenza is not clearly understood. Here we analyzed the spatial, age and temporal evolution of the 2009 A/H1N1 influenza pandemic in Chile, a southern hemisphere country covering a long and narrow strip comprising latitudes 17°S to 56°S.Methods: We analyzed the dissemination patterns of the 2009 A/H1N1 pandemic across 15 regions of Chile based on daily hospitalizations for severe acute respiratory disease and laboratory confirmed A/H1N1 influenza infection from 01-May to 31-December, 2009. We explored the association between timing of pandemic onset and peak pandemic activity and several geographical and demographic indicators, school vacations, climatic factors, and international passengers. We also estimated the reproduction number (R) based on the growth rate of the exponential pandemic phase by date of symptoms onset, estimated using maximum likelihood methods.Results: While earlier pandemic onset was associated with larger population size, there was no association with connectivity, demographic, school or climatic factors. In contrast, there was a latitudinal gradient in peak pandemic timing, representing a 16-39-day lag in disease activity from the southern regions relative to the northernmost region (P < 0.001). Geographical differences in latitude of Chilean regions, maximum temperature and specific humidity explained 68.5{\%} of the variability in peak timing (P = 0.01). In addition, there was a decreasing gradient in reproduction number from south to north Chile (P < 0.0001). The regional mean R estimates were 1.6-2.0, 1.3-1.5, and 1.2-1.3 for southern, central and northern regions, respectively, which were not affected by the winter vacation period.Conclusions: There was a lag in the period of most intense 2009 pandemic influenza activity following a South to North traveling pattern across regions of Chile, significantly associated with geographical differences in minimum temperature and specific humidity. The latitudinal gradient in timing of pandemic activity was accompanied by a gradient in reproduction number (P < 0.0001). Intensified surveillance strategies in colder and drier southern regions could lead to earlier detection of pandemic influenza viruses and improved control outcomes.",
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AU - Fuentes, Rodrigo

AU - Sotomayor, Viviana

AU - Simonsen, Lone

AU - Miller, Mark A.

AU - Lima, Mauricio

AU - Villarroel, Claudia

AU - Chiu, Monica

AU - Villarroel, Jose E.

AU - Olea, Andrea

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N2 - Background: The role of demographic factors, climatic conditions, school cycles, and connectivity patterns in shaping the spatio-temporal dynamics of pandemic influenza is not clearly understood. Here we analyzed the spatial, age and temporal evolution of the 2009 A/H1N1 influenza pandemic in Chile, a southern hemisphere country covering a long and narrow strip comprising latitudes 17°S to 56°S.Methods: We analyzed the dissemination patterns of the 2009 A/H1N1 pandemic across 15 regions of Chile based on daily hospitalizations for severe acute respiratory disease and laboratory confirmed A/H1N1 influenza infection from 01-May to 31-December, 2009. We explored the association between timing of pandemic onset and peak pandemic activity and several geographical and demographic indicators, school vacations, climatic factors, and international passengers. We also estimated the reproduction number (R) based on the growth rate of the exponential pandemic phase by date of symptoms onset, estimated using maximum likelihood methods.Results: While earlier pandemic onset was associated with larger population size, there was no association with connectivity, demographic, school or climatic factors. In contrast, there was a latitudinal gradient in peak pandemic timing, representing a 16-39-day lag in disease activity from the southern regions relative to the northernmost region (P < 0.001). Geographical differences in latitude of Chilean regions, maximum temperature and specific humidity explained 68.5% of the variability in peak timing (P = 0.01). In addition, there was a decreasing gradient in reproduction number from south to north Chile (P < 0.0001). The regional mean R estimates were 1.6-2.0, 1.3-1.5, and 1.2-1.3 for southern, central and northern regions, respectively, which were not affected by the winter vacation period.Conclusions: There was a lag in the period of most intense 2009 pandemic influenza activity following a South to North traveling pattern across regions of Chile, significantly associated with geographical differences in minimum temperature and specific humidity. The latitudinal gradient in timing of pandemic activity was accompanied by a gradient in reproduction number (P < 0.0001). Intensified surveillance strategies in colder and drier southern regions could lead to earlier detection of pandemic influenza viruses and improved control outcomes.

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KW - Climatological variables, Specific humidity

KW - Influenza-like-illness

KW - Reproduction number

KW - School cycles

KW - Spatial heterogeneity

KW - Temperature

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