Abstract
ObjectivesAlthough 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.Design and settingWeekly 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.ResultsThe 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.ConclusionsEpidemic 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.
Highlights
Influenza and other respiratory virus infections are the most common causes of primary care consultation and represent an important economic burden worldwide.[1,2,3,4] In a typical season, annual attack rate of influenza is estimated at 5 to 10% in adults and 20 to 30% in children[5], not all cases seek medical care and are captured by the surveillance systems
It is widely accepted that influenza surveillance should address the following objectives: monitoring the circulating virus strains, the timing, intensity and severity of the epidemic waves, providing information about the underlying risk conditions associated with severity as well as supplying epidemiological and virological support for pandemic early warning and preparedness.[6]
One of the most important indicators in influenza surveillance is the estimated incidence or percentage of consultations in a population in a given period, which are related to the intensity of seasonal epidemics
Summary
Influenza and other respiratory virus infections are the most common causes of primary care consultation and represent an important economic burden worldwide.[1,2,3,4] In a typical season, annual attack rate of influenza is estimated at 5 to 10% in adults and 20 to 30% in children[5], not all cases seek medical care and are captured by the surveillance systems. It is widely accepted that influenza surveillance should address the following objectives: monitoring the circulating virus strains, the timing, intensity and severity of the epidemic waves, providing information about the underlying risk conditions associated with severity as well as supplying epidemiological and virological support for pandemic early warning and preparedness.[6] Influenza surveillance is supported by quantitative and qualitative indicators aimed at assessing the burden of seasonal epidemics. Such indicators are principally based on clinical consultations in general practice, hospitalised laboratory-confirmed cases, sentinel and nonsentinel positive specimens, mortality and local outbreaks. Some countries remained at the baseline level throughout the entire surveillance period
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