Influenza virus activity in the world
15 February 2013
Based on FluNet reporting (as of 12 February 2013, 15:45 UTC), during weeks 4 to 5 (20 January 2013 to 2 February 2013), National Influenza Centres (NICs) and other national influenza laboratories from 87 countries, areas or territories reported data. The WHO GISRS laboratories tested more than 70 349 specimens. 20 711 were positive for influenza viruses, of which 15 121 (73%) were typed as influenza A and 5590 (27%) as influenza B. Of the sub-typed influenza A viruses, 4 801 (48%) were influenza A(H1N1)pdm09 and 5 137 (52%) were influenza A(H3N2). Of the characterized B viruses, 281 (86%) belong to the B-Yamagata lineage and 44 (14%) to the B-Victoria lineage.
During weeks 4 to 5, influenza activity remained high in the northern hemisphere and sporadic in the southern hemisphere. A(H3N2) viruses predominated, followed by A(H1N1)pdm09 and influenza B viruses.
Influenza activity continued to increase in Europe. Higher proportions of co-circulating A(H1N1)pdm09 and B viruses were detected in various parts of Europe. A(H3N2) co-circulated with both A(H1N1)pdm09 and B viruses but at a lower level. One A(H1N1)pdm09 virus with highly reduced inhibition to oseltamivir was reported.
A(H3N2) viruses remained the predominant virus subtype in North America. In Canada, laboratory confirmed detections of influenza remained at a similar level to that in previous weeks. In United States influenza activity continued to decrease.
In Asia, A(H3N2) viruses remained predominant. A(H3N2) activity remained high in China and Japan, an increase in activity was reported from Mongolia. In China Hong Kong Special Administrative Region, increased detections of A(H1N1)pdm09 and A(H3N2) were reported, signalling the start of the influenza season. A(H1N1)pdm09 viruses were also reported from India.
Sporadic detections of influenza viruses were reported from the African region. A(H1N1)pdm09 virus activity remained high in Algeria. Sporadic detections of A(H1N1)pdm09, A(H3N2) and B were reported from Burkina Faso, Cameroon and Ethiopia.
In Central and South America, influenza activity remained low with sporadic detections of all three circulating subtypes reported.