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EuroFlu - Weekly Electronic Bulletin - Week 7 : 11/02/2013-17/02/2013 - 22 February 2013, Issue No. 476: H1N1pdm09 dominant strain; SARI up

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  • EuroFlu - Weekly Electronic Bulletin - Week 7 : 11/02/2013-17/02/2013 - 22 February 2013, Issue No. 476: H1N1pdm09 dominant strain; SARI up

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


    EuroFlu - Weekly Electronic Bulletin - Week 7 : 11/02/2013-17/02/2013 - 22 February 2013, Issue No. 476

    Influenza activity remains at high levels in the east but started declining at the western part of the WHO European Region



    Summary, week 7/2013
    • Consultation rates for influenza-like illness (ILI) and/or acute respiratory infection (ARI) have continued to increase in the eastern part of the Region, but have started to decrease in some northern and western countries.
    • Influenza A(H1N1)pdm09, A(H3N2) and type B viruses continued to co-circulate in the Region, with A(H1N1)pdm09 predominant.
    • The number of reported hospitalizations due to severe acute respiratory infection (SARI) is increasing slowly in association with the increasing influenza activity in the eastern part of the Region.
    • The WHO Consultation on the Composition of Influenza Virus Vaccines for the Northern Hemisphere 2013?2014 took place this week, and the WHO expert group recommended updates of the A(H3N2) and B/Yamagata lineage components.
    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 07/2013 a total of 7044 specimens tested positive for influenza, with 4761 (68%) being influenza A (Fig. 1).

    In week 07/2013, influenza A(H1N1)pdm09 viruses remained the dominant A virus subtype: of 3568 subtyped, 2644 (74%) were A(H1N1)pdm09 while only 924 (26%) were A(H3N2) (Fig. 2a). These proportions of influenza A virus subtypes have remained stable for several weeks.

    Since the beginning of the season (week 40/2012), 47 426 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, 32 556 (69%) were influenza A and 14 870 (31%) influenza B (Fig. 2b).

    Of the 20 778 influenza A viruses that have been subtyped, 15 103 (73%) were A(H1N1)pdm09 and 5 675 (27%) were A(H3N2).

    In addition, the lineages for 1905 influenza B viruses were determined: 1727 (91%) belonged to the B/Yamagata lineage and 178 (9%) to B/Victoria.

    (?)

    Circulation of influenza viruses in week 07/2013 remained diverse, with influenza A, mainly A(H1N1)pdm09, reported as the dominant virus in countries in northern, eastern and central Europe, Iceland, 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 the United Kingdom (Northern Ireland) (Map 1).

    Between these areas, more countries than in week 06/2013 reported co-circulation of A(H1N1)pdm09, A(H3N2) and influenza B.



    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 headquarters web site).

    The WHO Consultation on the Composition of Influenza Virus Vaccines for the Northern Hemisphere 2013?2014 took place this week, and the WHO expert group recommended updates of the A(H3N2) and B/Yamagata lineage components (see more at WHO headquarters web site).

    An update of the A(H3N2) vaccine component was recommended because of antigenic changes in earlier egg-propagated A/Victoria/361/2011-like vaccine viruses resulting from adaptation to propagation in eggs. It was also recommended that the cell-propagated A/Victoria/361/2011-like vaccine virus be A/Texas/50/2012.

    The B/Yamagata lineage B/Wisconsin/1/2010-like virus (Clade 3) was replaced by the B/Massachusetts/2/2012-like (Clade 2) virus. This decision was based on the antigenic differentiation of Clade 2 and 3 viruses by some post-infection ferret antisera and the increase in the proportion of Clade 2 B/Yamagata lineage viruses over Clade 3 in Europe and many parts of the world.

    Since week 40/2012, 2001 influenza viruses characterized antigenically by 13 countries (Denmark, Germany, Greece, Italy, Latvia, Portugal, Romania, the Russian Federation, Slovakia, Slovenia, Spain, Switzerland and the United Kingdom (England, Scotland)) corresponded with the viruses recommended by WHO for inclusion in the current northern hemisphere seasonal influenza vaccine (Fig. 3).

    13 countries (Austria, Belgium, Denmark, Finland, Germany, Greece, Italy, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom (Scotland)) have characterized 552 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 prototype viruses, egg-propagated A/California/7/2009 and cell-propagated A/Victoria/361/2011, respectively. However, the A/Victoria/361/2011 egg-propagated vaccine virus has egg-induced antigenic changes compared with the cell-propagated A/Victoria/361/2011virus.
    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 (~90%). Influenza B viruses of the B/Victoria lineage all fall within the B/Brisbane/60/2008 genetic 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, with the proportion of viruses in Clade 2 markedly increasing. Viruses in these clades can be distinguished antigenically from each other by some post-infection ferret antisera, but remain antigenically similar to the current vaccine virus, B/Wisconsin/1/2010.



    Monitoring of susceptibility to antiviral drugs

    Since week 40/2012, 9 countries (Denmark, Germany, Greece, the Netherlands, Norway, Portugal, Spain, Sweden and the United Kingdom) have screened 284 viruses for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir.

    Of the 111 A(H1N1)pdm09 viruses tested, 110 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 98 influenza A(H3N2) and 75 influenza B viruses tested showed susceptibility to both drugs.

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



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

    More countries than last week, mainly in western and northern parts of the Region, reported decreasing influenza activity during week 07/2013 (Map 4), but with the majority still reporting medium intensity levels (Map 2) and widespread circulation of influenza (Map 3). Similar to week 06/2013, of the countries that have established epidemic thresholds, all but Ukraine reported ILI/ARI consultation rates above their national threshold levels.

    (?)

    In week 07/2013, 2634 sentinel specimens were tested of which 1313 (50%) were positive for influenza, similar to week 06/2013 (Fig. 5).

    In the 29 countries testing 20 or more sentinel specimens, influenza positivity ranged from 14% to 81%, with a median of 54% (mean: 49%).

    Of the 1313 influenza-positive specimens from sentinel sources, more were positive for influenza B (50%) than in week 06/2013. Most of the influenza B detections were reported by France, Italy and Spain (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 weekly number of SARI hospitalizations reached the highest level of the season to date.

    The proportion of respiratory specimens from patients with SARI that tested positive for influenza remained relatively stable over the last 2 weeks (Fig. 7) with most countries reporting cases predominantly in the group aged 0?4 years.

    Nevertheless, Kazakhstan and Ukraine reported increasing activity in the group aged 15?29; Serbia, in the group aged 30?64; and Slovakia, 15?64.

    Since the beginning of the season, the increase in SARI cases testing positive for influenza in Georgia, Romania and Ukraine is more or less in line with the increase in the reported number of SARI hospitalizations.


    For week 07/2013, 11 countries (Armenia, Belarus, Belgium, Georgia, Kazakhstan, Kyrgyzstan, the Republic of Moldova, Romania, the Russian Federation, Serbia and Ukraine) reported 107 influenza detections among 343 specimens tested, 91% of which were influenza A (Fig. 8a).

    Most of the detections were reported by 4 countries (Armenia, Georgia, the Russian Federation and Ukraine), in which influenza activity has been gradually increasing with influenza A(H1N1)pdm09 predominant.

    Since week 40/2012, 3715 SARI specimens have been collected and tested for influenza. The relative distribution of influenza types and subtypes in hospitalized SARI patients remains more or less in line with the results of outpatient surveillance. 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), 78 such cases were reported for week 07/2013, with most of them being influenza A. To date, A(H1N1)pdm09, A(H3N2) and influenza B have been detected among hospitalized patients with 56% of detected viruses being influenza A.

    For more information on surveillance of confirmed hospitalized influenza, please see ECDC?s Weekly Influenza Surveillance Overview (WISO) at European 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 7/2013, 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).

    (?)



    Country comments (where available)
    • Czech Republic: Up to end of week 7/2013 a cumulative total of 405 severe influenza patients with laboratory-confirmed influenza were reported by intensive and resuscitation care units including 85 deaths.
    • Republic of Moldova:
      • This 7th sentinel week were registered 2 cases of death from seasonal influenza A (H1N1) pdm (non-sentinel): two people of 55 and 51 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 7th sentinel week, 57 samples were tested for Influenza viruses, from which 27 samples were positive for RNA Influenza virus A(H1N1)pdm, 4 samples - positive for RNA Influenza virus A(H3N2) and 8 samples were positive for RNA Influenza virus type B.
    (?)


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