Weekly influenza surveillance overview, March 11, 2011 - Week 9

Most European Union/European Economic Area countries are reporting regional or widespread influenza activity, with medium influenza-like illness (ILI)/acute respiratory infection (ARI) consultation rates. Decreasing ILI/ARI trends were reported by the majority of countries.An increasing proportion of B viruses has been reported. In week 09/2011, 55.3% of influenza virus detections were type A, and 44.7% were type B. The latter are reported to be dominant now in a number of countries. Of the 784 subtyped influenza A viruses, 97.2% were A(H1N1)2009.In week 09/2011, ten countries reported 119 cases of all-cause severe acute respiratory infection (SARI) and hospitalised confirmed influenza cases. The latter were mostly due to influenza A(H1N1)2009 virus infection.Numbers of influenza virus infections with severe outcome have decreased in western European Union countries that report these. However, the number of cases remains high in Greece. Apart from the Czech Republic, Romania and Slovakia, there is considerable uncertainty about cases with severe respiratory disease due to influenza in a number of central and eastern European Union countries because of limited hospital surveillance for influenza-associated cases.