Seasonality of Influenza in Brazil: A Traveling Wave from the Amazon to the Subtropics

Wladimir J Alonso*, Cecile Viboud, Lone Simonsen, Eduardo W. Hirano, Luciane Z. Daufenbach, Mark Miller

*Corresponding author

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Influenza circulation and mortality impact in tropical areas have not been well characterized. The authors studied the seasonality of influenza throughout Brazil, a geographically diverse country, by modeling influenza-related mortality and laboratory surveillance data. Monthly time series of pneumonia and influenza mortality were obtained from 1979 to 2001 for each of the 27 Brazilian states. Detrended time series were analyzed by Fourier decomposition to describe the amplitude and timing of annual and semiannual epidemic cycles, and the resulting seasonal parameters were compared across latitudes, ranging from the equator (+5 degrees N) to the subtropics (-35 degrees S). Seasonality in mortality was most pronounced in southern states (winter epidemics, June-July), gradually attenuated toward central states (15 degrees S) (p < 0.001), and remained low near the equator. A seasonal southward traveling wave of influenza was identified across Brazil, originating from equatorial and low-population regions in March-April and moving toward temperate and highly populous regions over a 3-month period. Laboratory surveillance data from recent years provided independent confirmation that mortality peaks coincided with influenza virus activity. The direction of the traveling wave suggests that environmental forces (temperature, humidity) play a more important role than population factors (density, travel) in driving the timing of influenza epidemics across Brazil.
Original languageEnglish
JournalAmerican Journal of Epidemiology
Volume165
Issue number12
Pages (from-to)1434–1442
ISSN0002-9262
DOIs
Publication statusPublished - 2007
Externally publishedYes

Bibliographical note

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Keywords

  • Brazil
  • climate
  • geographic locations
  • influenza
  • human
  • mortality
  • pneumonia
  • seasons

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