title: Influenza epidemics in Iceland over 9 decades: changes in timing and synchrony with the United States and Europe.
abstract: Influenza epidemics exhibit a strongly seasonal pattern, with winter peaks that occur with similar timing across temperate areas of the Northern Hemisphere. This synchrony could be influenced by population movements, environmental factors, host immunity, and viral characteristics. The historical isolation of Iceland and subsequent increase in international contacts make it an ideal setting to study epidemic timing. The authors evaluated changes in the timing and regional synchrony of influenza epidemics using mortality and morbidity data from Iceland, North America, and Europe during the period from 1915 to 2007. Cross-correlations and wavelet analyses highlighted 2 major changes in influenza epidemic patterns in Iceland: first was a shift from nonseasonal epidemics prior to the 1930s to a regular winter-seasonal pattern, and second was a change in the early 1990s when a 1-month lag between Iceland and the United States and Europe was no longer detectable with monthly data. There was a moderate association between increased synchrony and the number of foreign visitors to Iceland, providing a plausible explanation for the second shift in epidemic timing. This suggests that transportation might have a minor effect on epidemic timing, but efforts to restrict air travel during influenza epidemics would likely have a limited impact, even for island populations.
authors.affiliation: Division of International Epidemiology and Population Studies, Fogarty International Center, National Institutes of Health, Bethesda, MD 20892, USA. dweinber@gmail.com
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Weinberger
authors.forename: Tyra Grove
authors.initials: TG
authors.lastname: Krause
authors.forename: Kåre
authors.initials: K
authors.lastname: Mølbak
authors.forename: Andrew
authors.initials: A
authors.lastname: Cliff
authors.forename: Haraldur
authors.initials: H
authors.lastname: Briem
authors.forename: Cécile
authors.initials: C
authors.lastname: Viboud
authors.forename: Magnus
authors.initials: M
authors.lastname: Gottfredsson
mesh_terms: D058872:Epidemics / Q000706:statistics & numerical data*; D005060:Europe / Q000453:epidemiology; D006801:Humans; D007055:Iceland / Q000453:epidemiology; D007251:Influenza, Human / Q000453:epidemiology*; D015233:Models, Statistical; D015999:Multivariate Analysis; D010507:Periodicity; D011159:Population Surveillance; D012621:Seasons; D014195:Travel; D014481:United States / Q000453:epidemiology; D014887:Weather