Weekly influenza surveillance overview February 04, 2011 - Week 4

Most European countries continue to report medium to high ILI/ARI consultation rates and widespread activity. Increasing trends are mainly observed in central, eastern and southern Europe whereas countries in western Europe are reporting declining trends.The proportion of influenza-positive sentinel specimens has decreased for the fourth consecutive week, dropping from 54% in peak week 52/2010 to 47% in week 4/2011.70% of influenza detections are type A, 30% are type B. More than 97% of subtyped influenza A viruses are A(H1N1) 2009.Since week 40/2010, nine countries have reported 2 488 all-cause SARI and hospitalised confirmed influenza-infected cases, including 154 fatalities. Overall, 43% of these cases were not known to have any underlying condition.In western countries with surveillance of severe cases, the numbers of new admissions requiring hospital care are generally dropping though numbers requiring higher level care remain substantial. Most of the severely affected cases are in the age group 15–64 years.