pandemic influenza




All of the 84 subtyped influenza viruses detected by sentinel networks in week 31/2009 were A(H1N1)v, and the UK (Northern Ireland) reported medium activity for the first time. Ireland and the UK (England, Northern Ireland) are the only countries that have reported influenza activity above their national baseline levels since the pandemic was declared.

Epidemiological situation - week 31/2009: For the intensity indicator, the national network levels for influenza-like illness (ILI) and/or acute respiratory infection (ARI), Ireland and the UK (England, Northern Ireland) reported medium activity. The highest consultation rates in Ireland and the UK (England, Northern Ireland) were observed among individuals aged 0—4 years and 15—64 years. For the geographical spread indicator, widespread activity was reported in the UK (England) and local activity was reported in Spain. The remaining countries reported sporadic (Belgium, Denmark, Hungary, Ireland, Latvia, Portugal, Slovenia and the UK (Northern Ireland)) or no activity (Bulgaria, Estonia, France, Germany, Greece, Lithuania, Romania, Slovakia and Sweden). The reported trends included an increase in Denmark and the UK (Northern Ireland), a decrease in Bulgaria, Latvia and the UK (England) and stability in the rest of the reporting countries.

Cumulative epidemiological situation - weeks 16—31/2009: Since week 16/2009, influenza activity above baseline levels was reported in the following locations: the UK (England) since week 27/2009, Ireland since week 30/2009, and UK (Northern Ireland) in week 31/2009. Influenza activity decreased in the UK (England) to medium in week 31/2009 after it was reported to be high in weeks 28—30. Influenza activity remained low in all other countries reporting to ECDC since week 16/2009.

Virological situation - week 31/2009: The total number of respiratory specimens collected by sentinel physicians in week 31/2009 was 584, of which 99 (17%) were positive for influenza virus: 84 (85%) were subtype A(H1N1)v and 15 A unsubtyped. The highest proportions of sentinel specimens positive for influenza were observed in Denmark (42%), Greece (40%) and Spain (29%). In addition, 2059 non-sentinel source specimens (e.g. specimens collected for diagnostic purposes in hospitals) were reported positive for influenza virus. Of these, 2056 were type A (1725 subtype (H1N1)v, two subtype H3N2 and 329 not subtyped) and three type B.

Cumulative virological situation - weeks 16—31/2009: Of the 11819 virus detections (sentinel and non-sentinel) since week 16/2009, 11369 (96%) were type A (7295 subtype (H1N1)v, 146 subtype H3, 106 subtype H3N2, 48 subtype H1, 38 subtype H1N1 and 3736 not subtyped) and 450 (4%) were type B. During week 31/2009, the proportion of sentinel specimens positive for influenza (17%) decreased compared to week 30/2009 when it was 27%, the highest since week 16/2009.

Based on the antigenic and/or genetic characterisation of 7080 influenza viruses reported from week 20/2008 to week 31/2009, 5178 (73%) were reported as A/Brisbane/10/2007 (H3N2)-like, 293 (4%) as A/Brisbane/59/2007 (H1N1)-like, 58 (1%) as B/Florida/4/2006-like (B/Yamagata/16/88 lineage), 1486 (21%) as B/Malaysia/2506/2004-like (B/Victoria/2/87 lineage) and 65 (1%) as A/California/7/2009 (H1N1)v-like. From this week onwards, we will report characterisations of the pandemic virus as A/California/7/2009 (H1N1)v-like in order to be in line with the current virus strains recommended by WHO for vaccine preparation. All A(H1N1)v viruses tested so far have been sensitive to oseltamivir and zanamivir—except for one specimen isolated in Denmark in a patient on oseltamivir treatment—but resistant to M2 inhibitors.

During week 31/2009, all the positive sentinel samples subtyped were the pandemic virus and of 1730 non-sentinel samples subtyped, only five were seasonal influenza strains. This indicates that the pandemic virus is the predominant circulating influenza virus. This does not, however, preclude the co-circulation of seasonal and pandemic influenza viruses during the winter period as circulation of seasonal strains during the summer is uncommon.

Background: The Weekly Electronic Bulletin presents and comments on influenza activity in the European Union and Norway. Of these countries, 14 reported both clinical and virological data, four reported virological data only and four reported clinical data only in week 31/2009. The spread of influenza viruses and their epidemiological impact in Europe are being monitored by the network under the aegis of the European Centre for Disease Prevention and Control in Stockholm (Sweden) in collaboration with the WHO Collaborating Centre for Reference and Research on Influenza in London (UK).

Source :
Weekly electronic bulletin Week 31: 27 July 2009 - 02 August 2009
07 August 2009


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