Weekly influenza surveillance overview, March 4, 2011 - Week 8

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 and widespread activity. Decreasing ILI/ARI trends were reported by the majority of countries.The proportion of influenza virus-positive sentinel specimens has gradually decreased to 36%, after peaking in week 52/2010 at around 56%.An increasing proportion of B viruses has been reported. In week 08/2011, 58% of influenza virus detections were type A, and 42% were type B. The latter are reported to be dominant now in a number of countries. Of the 1139 subtyped influenza A viruses, 99% were A(H1N1)2009.In week 08/2011, eleven countries reported 149 all-cause severe acute respiratory infection (SARI) and hospitalised confirmed influenza cases. The latter were mostly due to influenza virus A(H1N1)2009 infection.Numbers of influenza 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 other countries in central and eastern European Union countries because of limited hospital surveillance for influenza-associated cases.