Mapping Influenza Activity Across Europe

Abstract

ISEE-361 Objective: Pandemic threat stresses the importance of timely information on seasonal influenza activity and the matching of circulating influenza viruses with vaccine composition. Clinical and virologic influenza activity in Europe has been monitored since 1996 by the European Influenza Surveillance Scheme. Until now influenza activity in Europe is aggregated per country, thus ignoring important information on the geographic spread of influenza within and across countries. We aim to create international maps of the development and spread of seasonal influenza activity across Europe. Material and Methods: Within EISS, weekly data on influenza activity are collected through a network of sentinel physicians in the 30 contributing countries, who register the number of patients that consult them for influenza-like illness or acute respiratory infection. International mapping by means of interpolation techniques as one important tool of GIS requires harmonized data at a low scale of aggregation. However, the international comparability of the influenza consultation rates is limited due to differences in health care systems, use, and case definitions. Therefore, a method to harmonize data at practice level is explored, ie, calculation of an index relating influenza activity to local reference values of low and peak activity. Results: This pilot study results in maps of the development and spread of seasonal influenza activity across at least 6 adjacent European countries (Denmark, Germany, the Netherlands, Switzerland, England, and Czech Republic), based on indexed weekly influenza consultation rates. It also provides insight in difficulties, challenges, and future perspectives in using interpolation techniques to internationally map influenza activity. Conclusions: Mapping of influenza activity at European level is an essential step forward to further understand the geographic spread of influenza, and it offers a novel way to communicate timely information on seasonal influenza, eg, for early warning purposes.