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EuroFlu - Weekly Electronic Bulletin - Week 6 : 04/02/2013-10/02/2013 - 15 February 2013, Issue No. 475: H1N1pdm09 dominant subtype; increased elderly mortality

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  • EuroFlu - Weekly Electronic Bulletin - Week 6 : 04/02/2013-10/02/2013 - 15 February 2013, Issue No. 475: H1N1pdm09 dominant subtype; increased elderly mortality

    [Source: EuroFlu, full page: (LINK). Edited.]


    EuroFlu - Weekly Electronic Bulletin - Week 6 : 04/02/2013-10/02/2013 - 15 February 2013, Issue No. 475

    Influenza activity remains high in the WHO European Region



    Summary, week 6/2013
    • For week 06/2013 most countries in the European Region reported medium levels of influenza-like illness (ILI) and acute respiratory infection (ARI) clinical consultation rates, and the percentage of sentinel specimens testing positive for influenza remained high.
    • Influenza activity continued to progress from west to east across the Region, with A(H1N1)pdm09 remaining the dominant influenza virus in circulation.
    • Within hospital surveillance, most of the severe acute respiratory infection (SARI) specimens that tested positive for influenza this week contained influenza A(H1N1)pdm09 virus.
    The EuroFlu bulletin describes and comments on influenza activity in the 53 Member States in the WHO European Region to provide information to public health specialists, clinicians and the public on the timing of the influenza season, the spread of influenza, the prevalence and characteristics of circulating viruses (type, subtype and lineage) and severity.

    For a description of influenza surveillance in the WHO European Region see below.



    Virological surveillance for influenza

    During week 6/2013 the overall influenza positivity rate continued to increase in the WHO European Region. A total of 6403 specimens tested positive for influenza in week 06/2013, with 4282 (67%) being influenza A.

    This distribution has remained similar for several weeks (Fig. 1).

    As in the 2 previous weeks, influenza A(H1N1)pdm09 viruses were the dominant A virus subtype in week 6/2013.

    Of 2660 influenza A viruses subtyped in week 6/2013, 1987(75%) were A(H1N1)pdm09, while only 673 (25%) were A(H3N2) (Fig. 2a).

    Since the beginning of the season (week 40/2012), 39 090 influenza viruses from sentinel and non-sentinel sources have been detected and typed.

    The relative proportion of influenza virus types has remained consistent since week 47/2012: cumulatively, 27 017 (69%) were influenza A and 12 073 (31%) influenza B (Fig. 2b).

    Of 17180 influenza A viruses that have been subtyped, 12 437 (72%) were A(H1N1)pdm09 and 4 743 (28%) were A(H3N2) ? relative proportions similar to those seen in previous weeks.

    In addition, the lineage for 1506 influenza B viruses has been determined since week 40/2012: 1361 (90%) belonged to the B/Yamagata lineage and 145 (10%) to B/Victoria.

    (?)

    Circulation of influenza viruses in week 06/2013 remained similar to the two previous weeks, with influenza A, mainly A(H1N1)pdm09, reported as the dominant virus in countries in northern, eastern and central Europe, Portugal and Turkey, while influenza B was reported as the dominant virus in some countries in the southern part of the Region, as well as Ireland and the United Kingdom (Northern Ireland) (Map 1).

    Between these areas, co-circulation of A(H1N1)pdm09, A(H3N2) and influenza B was observed.



    Virus strain characterizations

    For the 2012/2013 northern hemisphere influenza season, WHO recommends inclusion of A/California/7/2009 (H1N1)pdm09-like, A/Victoria/361/2011 (H3N2)-like and B/Wisconsin/1/2010-like (from the B/Yamagata lineage) viruses in vaccines (see more at WHO web site).

    Since week 40/2012, 1710 influenza viruses characterized antigenically by 12 countries (Denmark, Germany, Greece, Italy, Latvia, Portugal, Romania, the Russian Federation, Slovakia, Slovenia, Switzerland and the United Kingdom (England and Scotland)) corresponded with the viruses recommended by WHO for inclusion in the current northern hemisphere seasonal influenza vaccine (Fig. 3).

    The United Kingdom characterized the majority of these viruses (925: 54%).

    Of the 790 A/Victoria/361/2011 (H3N2)-like viruses characterized this season 485 (61%) were characterized by Scotland. 13 countries (Austria, Belgium, Denmark, Finland, Germany, Greece, Italy, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom (Scotland)) have characterized 505 influenza viruses genetically (Fig. 4).

    # Included in the WHO-recommended composition of influenza virus vaccines for use in the 2012/2013 northern hemisphere influenza season.

    * Included in the WHO-recommended composition of influenza virus vaccines for use in the 2013 southern hemisphere influenza season.


    Both A(H1N1)pdm09 and A(H3N2) viruses have evolved to fall into a number of different genetic groups, which are all antigenically similar to their vaccine viruses, A/California/7/2009 and A/Victoria/361/2011, respectively.
    Influenza B viruses of the B/Victoria/2/87 and the B/Yamagata/16/88 lineages are co-circulating in the Region with dominance of the B/Yamagata lineage viruses this season (90%). Influenza B viruses of the B/Victoria lineage all fall within the B/Brisbane/60/2008 clade and are antigenically indistinguishable. B/Yamagata lineage viruses fall into two distinct genetic clades, represented by B/Estonia/55669/2011 (Clade 2) and B/Wisconsin/1/2010 (Clade 3) respectively. Viruses in these clades can be distinguished antigenically from each other, but remain antigenically similar to the current vaccine virus, B/Wisconsin/1/2010.



    Monitoring of susceptibility to antiviral drugs

    Since week 40/2012, 8 countries (Denmark, Germany, Greece, the Netherlands, Norway, Spain, Sweden and the United Kingdom) have screened 280 viruses for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir.

    The 97 influenza A(H3N2) and 74 influenza B viruses showed susceptibility to both drugs.

    Of the 109 A(H1N1)pdm09 viruses tested, 108 showed susceptibility to both drugs, 1 virus carrying the neuraminidase H275Y amino acid substitution, causing resistance to oseltamivir, was detected in the Netherlands in a hospitalized immunocompromised patient exposed to oseltamivir through treatment.

    The 14 influenza A(H3N2) and 10 influenza A(H1N1)pdm09 viruses screened for susceptibility to adamantanes were found to be resistant.



    Outpatient surveillance for influenza-like illness (ILI) and/or acute respiratory infection (ARI)

    Reported clinical data indicated that influenza activity continued to increase in most of the WHO European Region (Map 4), with the majority of countries reporting medium intensity levels (Map 2). At the same time, clinical activity in Denmark, Greece, Iceland, Ireland, the Netherlands, Norway and Poland peaked earlier in the season and has declined (see Country data and graphs for more details).

    Most of the countries across the Region reported widespread circulation of influenza for week 06/2013 (Map 3). All of the countries that have established epidemic thresholds reported ILI/ARI consultation rates above their national threshold levels.

    (?)

    Overall, 2635 sentinel specimens were tested, of which 1352 (51%) were positive for influenza in week 06/2013 ? a slight decrease in comparison with the previous week. (Fig. 5).

    In the 26 countries testing 20 or more sentinel specimens, influenza positivity ranged from 11% to 78%, with a median of 50% (mean: 46%).

    Of the 1352 influenza-positive specimens from sentinel sources, 56% were influenza A (Fig. 6a). Fig. 6b gives a detailed overview of cumulative influenza virus detections by type and subtype since week 40/2012. Click here for a detailed overview in a table format.

    (?)



    Hospital surveillance for SARI

    The number of hospitalizations, as well as the proportion of respiratory specimens from patients with SARI testing positive for influenza, remained relatively stable (Fig. 7) with most countries reporting cases mainly in the group aged 0?4 years.


    For week 06/2013, 13 countries (Albania, Armenia, Belarus, Belgium, Georgia, Kazakhstan, Kyrgyzstan, the Republic of Moldova, Romania, the Russian Federation, Serbia, Slovakia and Ukraine) reported 88 influenza detections among 304 specimens tested, 79% of which (70) were influenza A (Fig. 8a).

    Since week 40/2012, 3300 SARI specimens have been collected and tested for influenza. The relative distribution of influenza types and subtypes in hospitalized SARI patients remains similar to that observed from other sentinel data sources . Click here for a detailed overview in table format.

    (?)

    Among the countries reporting on hospitalization of severe influenza cases to the European Centre for Disease Prevention and Control (ECDC), 125 cases were reported for week 06/2013, with most of them being influenza A. To date, A(H1N1)pdm09, A(H3N2) and influenza B have been detected among hospitalized patients.

    For more information on surveillance of confirmed hospitalized influenza, please see ECDC?s Weekly Influenza Surveillance Overview (WISO) atEuropean Centre for Disease Prevention and Control web site.



    Respiratory syncytial virus (RSV)

    Based on the data presented by countries reporting on RSV, the positivity rate peaked in week 52/2012, after which the number of detections has continued to decrease gradually (see Country data and graphsfor individual country data).



    EuroMOMO (European Mortality Monitoring Project)

    EuroMOMO is a project set up to develop and operate a routine public health mortality monitoring system to detect and measure, on a real-time basis, excess deaths related to influenza and other possible public health threats across 20 European Union (EU) countries.

    Pooled analysis of week 6/2013, based on 14 countries or regions, showed increased mortality among older people. The results of pooled analysis may vary, depending on which countries are included in the weekly analysis. For more information about the EUROMOMO mortality monitoring system please click here)



    Description of influenza surveillance

    Most of the 53 Member States of the WHO European Region monitor influenza activity through surveillance of ILI and/or ARI in primary care clinics, with some countries also conducting hospital-based surveillance for severe disease. Surveillance data in the Region are collected from sentinel and non-sentinel systems. Sentinel data come from a network of designated clinicians who routinely and systematically collect respiratory specimens from ILI, ARI or SARI cases according to standard case definitions. Non-sentinel data come from a variety of other sources, including community outbreaks, general practitioners and hospitals that are not part of the sentinel surveillance system for influenza and may not use a standard case definition for ILI, ARI or SARI. The EuroFlu bulletin collates and interprets epidemiological and virological data from the different surveillance systems in the Region, to provide information on the timing of the influenza season, the spread of influenza, the prevalence and characteristics of circulating influenza viruses according to influenza type and subtype (A(H3N2) and A(H1N1)pdm09) or lineage (B/Victoria of B/Yamagata), and severity. In addition, influenza viruses are assessed each season for their antigenic and genetic characteristics, to determine the extent of their antigenic and genetic similarity to the viruses included in the seasonal influenza vaccine and the prevalence of mutations that affect pathogenicity or are associated with reduced susceptibility to antiviral drugs.

    (?)



    Country comments (where available)
    • Denmark: In Denmark, the season so far has been dominated by A(H3N2) viruses, mainly devided into two genetic groups. Now we are experiencing an increase in influenza B-Yamagata
    • Czech Republic: Up to end of week 6/2013 a cumulative total of 350 severe influenza patients with laboratory-confirmed influenza were reported by intensive and resuscitation care units including 68 deaths. Further details regarding current influenza situation were published as Rapid Communication paper in Eurosurveillance on 7 February 2013 at http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=20396
    • Republic of Moldova: This week were registered 2 cases of death from seasonal influenza A (H1N1) pdm (non-sentinel): a person of 42 years, female, Ungheni district; and a person of 62 years, male, Chisinau. In both cases patients asked late for medical care, antiviral treatment was initiated late. Both people have not been vaccinated against influenza. This 6th sentinel week, 42 samples were tested for Influenza viruses, from which 14 samples were positive for RNA Influenza virus A(H1N1)pdm, 2 samples - positive for RNA Influenza virus A(H3N2) and 7 samples were positive for RNA Influenza virus type B.
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