Influenza in Tropical Regions

Abstract:  The global burden of influenza on morbidity and mortality is considerable, with an estimated 1 million annual deaths worldwide. In temperate regions, there are clear seasonal variations in the occurrence of influenza, with a marked peak in cold winter months. In contrast, seasonality is less defined in tropical regions—here, there is high background influenza activity throughout the year, on top of which epidemics occur at intermediate months between the influenza season in temperate countries of the Northern and Southern hemispheres. Influenza seasonal patterns in the Americas are summarized, which illustrates the transition between the Northern and Southern hemispheres. Very little is known about exactly how and why the seasonality of influenza varies with latitude. No link with environmental conditions has been convincingly shown, although influenza activity appears to coincide with the rainy season in some tropical countries. Citati on: Viboud C, Alonso WJ, Simonsen L (2006) Influenza in Tropical Regions. PLoS Med 3(4): e89. doi:10.1371/journal. pmed.0030089