title: Influenza surveillance in Europe: comparing intensity levels calculated using the moving epidemic method.
abstract: OBJECTIVE
  Although influenza-like illnesses (ILI) and acute respiratory illnesses (ARI) surveillance are well established in Europe, the comparability of intensity among countries and seasons remains an unresolved challenge. The objective is to compare the intensity of ILI and ARI in some European countries.
  
  
  METHODS
  Weekly ILI and ARI incidence rates and proportion of primary care consultations were modeled in 28 countries for the 1996/1997-2013/2014 seasons using the moving epidemic method (MEM). We calculated the epidemic threshold and three intensity thresholds, which delimit five intensity levels: baseline, low, medium, high, and very high. The intensity of 2013/2014 season is described and compared by country.
  
  
  RESULTS
  The lowest ILI epidemic thresholds appeared in Sweden and Estonia (below 10 cases per 100 000) and the highest in Belgium, Denmark, Hungary, Poland, Serbia, and Slovakia (above 100 per 100 000). The 2009/2010 season was the most intense, with 35% of the countries showing high or very high intensity levels. The European epidemic period in season 2013/2014 started in January 2014 in Spain, Poland, and Greece. The intensity was between low and medium and only Greece reached the high intensity level, in weeks 7 to 9/2014. Some countries remained at the baseline level throughout the entire surveillance period.
  
  
  CONCLUSIONS
  Epidemic and intensity thresholds varied by country. Influenza-like illnesses and ARI levels normalized by MEM in 2013/2014 showed that the intensity of the season in Europe was between low and medium in most of the countries. Comparing intensity among seasons or countries is essential for understanding patterns in seasonal epidemics. An automated standardized model for comparison should be implemented at national and international levels.
authors.affiliation: Public Health Directorate, Castilla y León Regional Health Ministry, Valladolid, Spain.
authors.forename: Tomás
authors.initials: T
authors.lastname: Vega
authors.affiliation: Public Health Directorate, Castilla y León Regional Health Ministry, Valladolid, Spain.
authors.forename: José E
authors.initials: JE
authors.lastname: Lozano
authors.affiliation: The Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors.forename: Tamara
authors.initials: T
authors.lastname: Meerhoff
authors.affiliation: European Centre for Disease Prevention and Control, Stockholm, Sweden.
authors.forename: René
authors.initials: R
authors.lastname: Snacken
authors.affiliation: European Centre for Disease Prevention and Control, Stockholm, Sweden.
authors.forename: Julien
authors.initials: J
authors.lastname: Beauté
authors.affiliation: Division of Health Security, Infectious Diseases and the Environment, WHO Regional Office for Europe, Copenhagen, Denmark.
authors.forename: Pernille
authors.initials: P
authors.lastname: Jorgensen
authors.affiliation: National Influenza Centre, University of Valladolid, Valladolid, Spain.
authors.forename: Raúl
authors.initials: R
authors.lastname: Ortiz de Lejarazu
authors.affiliation: Health Protection Surveillance Centre, Dublin, Ireland.
authors.forename: Lisa
authors.initials: L
authors.lastname: Domegan
authors.affiliation: Laboratoire National de Santé, Luxembourg, Luxembourg.
authors.forename: Joël
authors.initials: J
authors.lastname: Mossong
authors.affiliation: Statens Serum Institute, Copenhagen, Denmark.
authors.forename: Jens
authors.initials: J
authors.lastname: Nielsen
authors.affiliation: Division of Communicable Diseases, Federal Office of Public Health, Directorates of Public Health, Bern, Switzerland.
authors.forename: Rita
authors.initials: R
authors.lastname: Born
authors.affiliation: CIBER Epidemiología y Salud Pública (CIBERESP), Institute of Health Carlos III, Madrid, Spain.
authors.forename: Amparo
authors.initials: A
authors.lastname: Larrauri
authors.affiliation: Division of Health Security, Infectious Diseases and the Environment, WHO Regional Office for Europe, Copenhagen, Denmark.
authors.forename: Caroline
authors.initials: C
authors.lastname: Brown
mesh_terms: D058872:Epidemics; D062665:Epidemiological Monitoring; D005060:Europe / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D007251:Influenza, Human / Q000453:epidemiology*; D012621:Seasons
keywords: Incidence; influenza-like illnesses; primary care; surveillance