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EuroFlu - Weekly Electronic Bulletin - Week 12 : 18/03/2013-24/03/2013 - 29 March 2013, Issue No. 481: Still high virus activity, but declining activity

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  • EuroFlu - Weekly Electronic Bulletin - Week 12 : 18/03/2013-24/03/2013 - 29 March 2013, Issue No. 481: Still high virus activity, but declining activity

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


    EuroFlu - Weekly Electronic Bulletin - Week 12 : 18/03/2013-24/03/2013 - 29 March 2013, Issue No. 481

    Declining influenza activity in Europe, despite high positivity rates


    Summary, week 12/2013
    • Consultation rates for influenza-like illness (ILI) and/or acute respiratory infection (ARI) continue to decrease throughout the WHO European Region, reaching preseason levels in some western countries.
    • The percentage of specimens testing positive for influenza, as well as the number of tests performed, continues to decline, but remains high in several countries.
    • Based on data from sentinel sources, influenza A(H1N1)pdm09 and influenza B continue to co-circulate, but the ratio of influenza B to influenza A is increasing.
    • The number of SARI hospitalizations as well as influenza positivity rate among cases of severe acute respiratory infection (SARI) decreased, with influenza A(H1N1)pdm09 being responsible for around half of the influenza detections.
    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 12/2013 a total of 3418 specimens tested positive for influenza, with 1864 (55%) positive for influenza A (Fig. 1). The proportion of influenza A viruses among total influenza detections has decreased since week 03/2013, when it was 76% of influenza-positive specimens.

    As in previous weeks, influenza A(H1N1)pdm09 remained the dominant type A virus in the Region: of 1206 subtyped, 709 (59%) were A(H1N1)pdm09 and 497 (41%) were A(H3N2) (Fig. 2a).

    Since the beginning of the season (week 40/2012), 82 410 influenza viruses from sentinel and non-sentinel sources have been detected and typed. Since week 47/2012, influenza A has been the most commonly detected virus: cumulatively, 53 371 (65%) were influenza A and 29 039 (35%) influenza B (Fig. 2b).

    Of the 34 285 influenza A viruses that have been subtyped, 23 851 (70%) were A(H1N1)pdm09 and 10 434 (30%) were A(H3N2).

    In addition, the lineage for 4735 influenza B viruses has been determined: 4333 (92%) belonged to the B/Yamagata lineage and 402 (8%) to B/Victoria.

    (?)

    Circulation of influenza viruses in week 12/2013 remained diverse across the Region, with an increasing number of countries in different parts of the Region reporting the dominance of influenza B or co-circulation of influenza A and B. Estonia, Greece and Ireland reported influenza A as the dominant virus (Map 1).


    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 the WHO headquarters web site).

    For the recommendations for the 2013/2014 northern hemisphere influenza season (see the WHO headquarters web site).

    Since week 40/2012, 4530 influenza viruses characterized antigenically by 14 countries (Austria, Denmark, Germany, Greece, Italy, Latvia, Portugal, Romania, the Russian Federation, Slovakia, Slovenia, Spain, Switzerland and the United Kingdom (England and Scotland)).

    The great majority corresponded with the viruses recommended by WHO for inclusion in the current northern hemisphere seasonal influenza vaccine (Fig. 3).

    The United Kingdom characterized 1245 of these viruses (27%). Scotland reported on 495 (33%) of the 1396 A/Victoria/361/2011 (H3N2)-like viruses characterized this season.

    15 countries (Austria, Belgium, Denmark, Finland, Germany, Greece, Ireland, Italy, Norway, Portugal, the Russian Federation, Spain, Sweden, Switzerland and the United Kingdom (Scotland)) have characterized 1154 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

    Cumulatively since week 40/2012, 12 countries (Denmark, Germany, Greece, the Netherlands, Norway, Portugal, Romania, the Russian Federation, Spain, Sweden, Switzerland and the United Kingdom) have screened 1165 viruses for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir.

    Of the 569 A(H1N1)pdm09 viruses tested, 560 showed susceptibility to both drugs while 9 viruses (2%) carrying the neuraminidase H275Y amino acid substitution, causing resistance to oseltamivir, were detected.

    Of these 9 viruses, 1 from the Russian Federation was detected in a hospitalized patient not exposed to oseltamivir through treatment; 2 viruses from the United Kingdom were detected in outpatients not exposed to oseltamivir through treatment; and 6 viruses were detected in hospitalized immunocompromised patients exposed to oseltamivir through treatment (1 from Denmark, 2 from Germany, 2 from the Netherlands and 1 from Switzerland).

    The 272 influenza A(H3N2) viruses tested showed susceptibility to both drugs.

    Of the 324 influenza B viruses tested, 323 showed susceptibility to both drugs; 1 virus showing reduced inhibition for oseltamivir, and normal inhibition for zanamivir, was detected in the United Kingdom in an outpatient without exposure to antiviral treatment. There is no indication of the spread of resistant viruses.

    The 99 influenza A(H1N1)pdm09 and 42 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)

    Latvia and Poland were the only countries that reported increasing influenza activity for week 12/2013 (Map 4). Similarly to week 11/2013, only Bosnia and Herzegovina reported high intensity (Map 2). At the same time, most countries continued reporting widespread/regional circulation of influenza (Map 3).

    Of the countries that have established epidemic thresholds, 7 (the Czech Republic, France, Ireland, Israel Kyrgyzstan, Kazakhstan and Romania) reported ILI/ARI consultation rates below their national threshold levels. In Denmark, Serbia and Switzerland, ILI/ARI consultation rates reached the baseline levels during week 12/2013.

    (?)

    The percentage of sentinel specimens testing positive for influenza has gradually decreased since week 10/2013; during week 12/2013, 1109 sentinel specimens were tested of which 445 (40%) were positive for influenza (Fig. 5).

    In the 18 countries testing 20 or more sentinel specimens, influenza positivity ranged from 9% to 100%, with a median of 43% (mean: 44%).

    Of the 445 influenza-positive specimens from sentinel sources, 67% were positive for influenza B. This proportion has gradually increased since week 03/2013 (Fig. 6a). Influenza B is becoming more predominant in countries where circulation of A(H1N1)pdm09 is decreasing.

    As in the 2 previous weeks, most of these detections were reported by France, Germany and Spain. 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

    In week 12/2013 the number of SARI hospitalizations and influenza positivity rate among SARI cases decreased in comparison with previous weeks (Fig. 7).

    This trend indicates that SARI hospitalization has peaked for the season in Belgium, Kyrgyzstan, the Russian Federation and Slovakia, concurrently with overall declines in outpatient ILI or ARI consultation rates.

    In general, at the beginning of the season, a relatively large portion of sentinel SARI hospitalizations occurred in the group aged 0?4. With increases in influenza activity, there have been associated increases in the relative proportions of SARI hospitalizations in older children, young adults and adults.

    For week 12/2013, 12 countries (Armenia, Belarus, Belgium, Georgia, Kazakhstan, Kyrgyzstan, the Republic of Moldova, Romania, the Russian Federation, Serbia, Slovakia and Ukraine) reported 72 influenza detections among 268 specimens tested, 49% of which were influenza A (Fig. 8a).

    Similarly to previous weeks, a few countries (Armenia, Georgia, Romania, the Russian Federation) reported most of the detections. Since week 40/2012, 60 39 SARI specimens have been collected and tested for influenza. 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), 24 such cases were reported for week 12/2013. 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) 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 graphs for individual country data).


    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)

    Republic of Moldova: During week 12/2013, 1 death from seasonal influenza A (H3N2) (non-sentinel) were registered: one person of 33 years, female, Strășeni district. Patient asked late for medical care, antiviral treatment was initiated late and has not been vaccinated against influenza. In addition, 36 samples were tested for Influenza viruses, of which 5 were positive for RNA influenza virus A(H1N1)pdm09; 2 samples, positive for RNA influenza virus A(H3N2); 11 samples, positive for RNA influenza virus type B; and 2, for RNA influenza virus A(H1N1)pdm09 + B.

    (?)


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