title: Associations between Meteorological Parameters and Influenza Activity in Berlin (Germany), Ljubljana (Slovenia), Castile and León (Spain) and Israeli Districts.
abstract: BACKGROUND
  Studies in the literature have indicated that the timing of seasonal influenza epidemic varies across latitude, suggesting the involvement of meteorological and environmental conditions in the transmission of influenza. In this study, we investigated the link between meteorological parameters and influenza activity in 9 sub-national areas with temperate and subtropical climates: Berlin (Germany), Ljubljana (Slovenia), Castile and León (Spain) and all 6 districts in Israel.
  
  
  METHODS
  We estimated weekly influenza-associated influenza-like-illness (ILI) or Acute Respiratory Infection (ARI) incidence to represent influenza activity using data from each country's sentinel surveillance during 2000-2011 (Spain) and 2006-2011 (all others). Meteorological data was obtained from ground stations, satellite and assimilated data. Two generalized additive models (GAM) were developed, with one using specific humidity as a covariate and another using minimum temperature. Precipitation and solar radiation were included as additional covariates in both models. The models were adjusted for previous weeks' influenza activity, and were trained separately for each study location.
  
  
  RESULTS
  Influenza activity was inversely associated (p<0.05) with specific humidity in all locations. Minimum temperature was inversely associated with influenza in all 3 temperate locations, but not in all subtropical locations. Inverse associations between influenza and solar radiation were found in most locations. Associations with precipitation were location-dependent and inconclusive. We used the models to estimate influenza activity a week ahead for the 2010/2011 period which was not used in training the models. With exception of Ljubljana and Israel's Haifa District, the models could closely follow the observed data especially during the start and the end of epidemic period. In these locations, correlation coefficients between the observed and estimated ranged between 0.55 to 0.91and the model-estimated influenza peaks were within 3 weeks from the observations.
  
  
  CONCLUSIONS
  Our study demonstrated the significant link between specific humidity and influenza activity across temperate and subtropical climates, and that inclusion of meteorological parameters in the surveillance system may further our understanding of influenza transmission patterns.
authors: Goddard Earth Sciences Technology and Research, Universities Space Research Associations, Columbia, Maryland, United States of America; Global Change Data Center, NASA Goddard Space Flight Center, Greenbelt, Maryland, United States of America.
authors: Radina P
authors: RP
authors: Soebiyanto
authors: Regional Office for Europe, World Health Organization, Copenhagen, Denmark; Influenza Division, U.S. Centers for Disease Control and Prevention (CDC), Atlanta, Georgia, United States of America.
authors: Diane
authors: D
authors: Gross
authors: Regional Office for Europe, World Health Organization, Copenhagen, Denmark.
authors: Pernille
authors: P
authors: Jorgensen
authors: Robert Koch Institute, Berlin, Germany.
authors: Silke
authors: S
authors: Buda
authors: Israel Center for Disease Control, Ministry of Health, Tel-Hashomer, Israel.
authors: Michal
authors: M
authors: Bromberg
authors: Israel Center for Disease Control, Ministry of Health, Tel-Hashomer, Israel.
authors: Zalman
authors: Z
authors: Kaufman
authors: Laboratory for Virology, National Institute of Public Health Slovenia, Ljubljana, Slovenia.
authors: Katarina
authors: K
authors: Prosenc
authors: Communicable Diseases and Environmental Health Care, National Institute of Public Health, Ljubljana, Slovenia.
authors: Maja
authors: M
authors: Socan
authors: Public Health Directorate, Health Department, Valladolid, Spain.
authors: Tomás
authors: T
authors: Vega Alonso
authors: Influenza Division, U.S. Centers for Disease Control and Prevention (CDC), Atlanta, Georgia, United States of America.
authors: Marc-Alain
authors: MA
authors: Widdowson
authors: Global Change Data Center, NASA Goddard Space Flight Center, Greenbelt, Maryland, United States of America.
authors: Richard K
authors: RK
authors: Kiang
mesh_terms: D001604:Berlin / Q000453:epidemiology; D006801:Humans; D006813:Humidity; D015994:Incidence; D007251:Influenza, Human / Q000453:epidemiology*; D007557:Israel; D008685:Meteorological Concepts; D012111:Residence Characteristics; D017524:Slovenia / Q000453:epidemiology; D013030:Spain / Q000453:epidemiology; D013696:Temperature