The consistent seasonal signal that characterizes annual influenza epidemics has long suggested a causal link between the physical environment and the transmission of influenza. Yet, despite considerable interest--dating as far back as Hippocrates--the environmental factors that facilitate the seasonal spread of influenza remain unclear. Historically, significant study of influenza seasonality was based almost exclusively on temperate regions,.due to a lack of high-quality influenza data in low-latitudes. In turn, although numerous hypotheses have been forwarded to explain the seasonal nature of influenza in temperate regions, few acknowledge the seasonal patterns in lower latitudes.This dissertation examines the scientific evidence for the seasonal mechanisms that potentially explain the complex seasonal patterns of influenza disease activity across the latitudinal gradient extending from temperate to tropical regions. I identified seasonal climatic variables that are potentially responsible for influenza seasonality from observational, experimental, ecological and anecdotal studies. I then used a global database of influenza seasonality to assess the consistency of relationships between influenza seasonality and the seasonality of relevant climatic variables. I determined that no single climatic variable is consistently correlated with seasonal influenza activity across temperate, subtropical and tropical regions.However, I did find a significant U-shaped relationship between specific humidity and influenza epidemics globally with epidemics becoming increasingly likely as specific humidity increases or decreases from approximately 12 g/kg. Further, I examined the temporal and spatial variation of influenza activity and specific humidity during the 2009 A/H1N1 pandemic across Mexico, which spans temperate, subtropical and tropical regions. I show that specific humidity may have modified the progression of three distinct waves of infection during the pandemic. These patterns are in agreement with the U-shaped relationship between specific humidity and seasonal influenza epidemics observed at a global scale. In all, this is the first time that relationships between climate and influenza (both seasonal and pandemic) activity have been successfully synthesized into a single parsimonious model across temperate, subtropical and tropical regions.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/145431 |
| Date | January 2011 |
| Creators | Tamerius, James Derek |
| Contributors | Comrie, Andrew C., Yool, Stephen R., Ernst, Kacey, Viboud, Cecile |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | English |
| Detected Language | English |
| Type | Electronic Dissertation, text |
| Rights | Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. |
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