In all reporting countries but one, influenza activity continued to decline or had already returned to baseline levels. After more than three months of active transmission, the 2012–2013 influenza season is on the wane, concludes the Weekly Influenza Surveillance Overview for week 11.
Of the 29 countries reporting for week 11, 19 countries reported medium intensity and 10 countries reported low intensity of influenza activity. No country reported high intensity, indicating a decline in influenza activity in an increasing number of countries. Decreasing or stable trends were reported by 28 countries and an increasing trend was only reported by Romania.
Virological surveillance shows that the overall proportion of influenza-positive cases among tested specimens has dropped from 54% for week 10 to 46% for week 11. The peak of 61% positive specimens this season was observed in week 5 in early February.
Since week 40/2012, 48% of sentinel specimens positive for influenza virus have been of type A and 52% of type B. Of influenza A viruses subtyped, the proportion of A(H1N1)pdm09 viruses has been 63%.