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EuroFlu - Weekly Electronic Bulletin - Week 14 : 31/03/2014-06/04/2014 - 11 April 2014, Issue No. 525: Flu at pre-season level in most Europe

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  • EuroFlu - Weekly Electronic Bulletin - Week 14 : 31/03/2014-06/04/2014 - 11 April 2014, Issue No. 525: Flu at pre-season level in most Europe

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


    EuroFlu - Weekly Electronic Bulletin - Week 14 : 31/03/2014-06/04/2014 - 11 April 2014, Issue No. 525

    Influenza activity returns to pre-season levels in most countries in the WHO European Region


    Summary, week 14/2014
    • Influenza activity has decreased in recent weeks in the majority of countries in the WHO European Region.
    • Clinical influenza-like illness (ILI) and/or acute respiratory infection (ARI) rates were below epidemic thresholds in 19 of 20 countries.
    • A small rise in the percentage of positive specimens was observed in week 14/2014 despite a further reduction in the number of specimens tested positive for influenza.
    • The number of cases with severe acute respiratory infection (SARI) has been decreasing and specimens testing positive for influenza have also declined during recent weeks.
    • Influenza A(H1N1)pdm09 and A(H3N2) viruses continue to co-circulate in the Region, with very few influenza B detections having been reported throughout the season.
    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 14/2014, the total number of specimens tested for influenza continued to decline: 9512 specimens from sentinel and non-sentinel sources were tested.

    Only 1485 (16%) were positive: 1316 (89%) for influenza A and 169 (11%) for influenza B (Fig. 1 and 2). The apparent rise in percentage of influenza B viruses is due to falling numbers of influenza A viruses being detected; the actual numbers of influenza B detections have been low but similar for a number of weeks.
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    Influenza A has remained the dominant virus type in circulation across the Region since the start of weekly monitoring in week 40/2013.

    Of the 716 influenza A viruses that were subtyped during week 14/2014, 318 (44%) were A(H1N1)pdm09 and 398 (56%) A(H3N2) (Fig. 2a).

    Since week 40/2013, sentinel and non-sentinel sources have yielded 41 860 influenza detections: 39 772 (95%) were influenza A and 2088 (5%) influenza B viruses (Fig. 2b).

    Of the 27 576 influenza A viruses that have been subtyped, 15 939 (58%) were A(H1N1)pdm09 and 11 637 (42%) were A(H3N2).

    In addition, the lineage of 172 influenza B viruses has been determined: 158 (92%) belonged to the B/Yamagata lineage (the lineage of the B virus recommended by WHO for inclusion in trivalent seasonal influenza vaccines) and 14 (8%) to the B/Victoria lineage.
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    With the decline of influenza activity in the Region, fewer countries than in previous weeks reported on dominant influenza type.

    Of the 38 countries supplying such data, only 20 reported influenza A as dominant in week 14/2014.

    Turkey was the only country reporting influenza B as dominant, but the number of detections was low (Map 1 and country table).

    Of countries providing data on dominant subtypes, influenza A(H3N2) was reported as dominant in 9 countries (Belgium, Germany, Ireland, Lithuania, the Netherlands, Romania, the Russian Federation, Slovenia and Switzerland), while only 3 countries (Denmark, Spain and the United Kingdom (Scotland and Wales)) reported A(H1N1)pdm09 as dominant. 4 countries (Estonia, France, Greece and Latvia) reported A(H1N1)pdm09 and A(H3N2) as co-dominant.


    Virus strain characterizations

    Circulating influenza viruses are assessed each season for their antigenic and genetic characteristics, to determine the extent of their antigenic similarity to the viruses included in the seasonal influenza vaccine, and determine the prevalence of mutations that affect pathogenicity or are associated with susceptibility to antiviral drugs.

    For the 2013/2014 northern hemisphere influenza season, WHO recommended inclusion of A/California/7/2009 (H1N1)pdm09-like, A/Texas/50/2012 (H3N2)-like and B/Massachusetts/2/2012-like (Yamagata lineage) viruses in vaccines (see the WHO headquarters web site).

    The WHO Consultation on the Composition of Influenza Virus Vaccines for the Northern Hemisphere 2014–2015 took place in week 7/2014, and the WHO expert group recommended no change from the vaccine composition for the 2013–2014 season. (see the WHO headquarters web site).

    Since week 40/2013, 1906 influenza viruses characterized antigenically by 15 countries (the Czech Republic, Denmark, Finland, Germany, Ireland, Latvia, the Netherlands, Norway, Portugal, Romania, the Russian Federation, Slovakia, Slovenia, 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).

    14 countries (Belgium, the Czech Republic, Denmark, Finland, Germany, Greece, Ireland, the Netherlands, Norway, Portugal, the Russian Federation, Spain, Sweden and Switzerland) have characterized 937 influenza viruses genetically (Fig. 4).
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    # Included in the WHO-recommended composition of influenza virus vaccines for use in the 2013/2014 northern hemisphere influenza season.

    * Included in the WHO-recommended composition of influenza virus vaccines for use in the 2014 southern hemisphere influenza season.


    Monitoring of susceptibility to antiviral drugs

    Since week 40/2013, 9 countries (Greece, the Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, the Russian Federation and the United Kingdom (England)) have screened 1296 viruses for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir.

    Of the 990 A(H1N1)pdm09 viruses tested, 975 showed susceptibility to both drugs; 15 viruses carrying the neuraminidase H275Y amino acid substitution, causing resistance to oseltamivir, were identified.

    Of these 15 viruses, 14 were detected in the United Kingdom in hospitalized patients, most of whom were treated with neuraminidase inhibitors, and 1 virus from Switzerland was detected in a hospitalized immunocompromised patient treated with oseltamivir.

    Of the 261 influenza A(H3N2) viruses tested, 260 showed susceptibility to both drugs. The remaining virus, detected in the United Kingdom in a hospitalized immunocompromised patient treated with oseltamivir, carried the neuraminidase E119V amino acid substitution, and showed reduced inhibition by oseltamivir but normal inhibition by zanamivir.

    All 45 influenza B viruses tested showed susceptibility to both oseltamivir and zanamivir.

    So far, there is no indication of increased resistance to the neuraminidase inhibitors during the winter of 2013/2014. All 135 influenza A(H1N1)pdm09 and 84 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)

    During week 14/2014, most European countries reported low-intensity influenza activity (Map 2), but with 4 countries reporting increasing trends (Map 4). In terms of geographic spread, influenza activity was sporadic in the majority of countries (Map 3).

    During week 14/2014, consultation rates continued to decline in most countries in the Region.

    Of the 20 countries with established national epidemic thresholds, the rates were below threshold levels in 19 countries. In a number of northern, western and central countries (the Czech Republic, Denmark, Germany, Latvia, Lithuania, Luxembourg, the Netherlands, Norway, Slovakia, Switzerland and the United Kingdom (England)), consultation rates have remained very low since the beginning of the season (mostly below the threshold) and much lower than last season.

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    The percentage of positive sentinel ILI/ARI specimens decreased slowly between week 8 and week 13/2014, but increased in week 14/2014 (Fig. 5).
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    During week 14/2014, 178 (27%) of the 654 specimens collected from sentinel sources tested positive for influenza virus; the majority were influenza A(H3N2) (Fig. 6a), similar to immediately preceding weeks. The number of influenza B detections remained low but has increased slightly over recent weeks. Click here for a detailed overview in a table format.
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    Hospital surveillance for SARI

    For sentinel surveillance of severe disease due to influenza, in week 14/2014 the number of SARI hospitalizations continued to decrease, with most cases reported being in those aged 0–4 years. The percentage of SARI patients who tested positive for influenza also decreased (Fig. 7).
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    During week 14/2014, 25 (18%) of the 141 SARI samples collected through sentinel surveillance in Armenia, Belarus, Georgia, Kazakhstan, Kyrgyzstan, the Republic of Moldova, Romania, the Russian Federation, Serbia and Ukraine tested positive for influenza. 23 were influenza A (1 A not subtyped, 10 A(H3N2), 12 A(H1N1)pdm09) and 2 were influenza B (Fig. 8a). Click here for a detailed overview in table format.
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    For week 14/2014, 5 countries (France, Ireland, Romania, Spain and the United Kingdom) reported 75 hospitalized laboratory-confirmed influenza cases. Influenza A virus was detected in 73 cases and influenza B in 2.

    Since week 40/2013, 7 countries have reported 4524 hospitalized laboratory-confirmed influenza cases: 4471 (99%) were related to influenza virus type A infection and 53 (1%) to type B.

    Of 3047 subtyped influenza A viruses, 2269 (74%) were A(H1)pdm09 and 778 (26%) were A(H3).

    A higher proportion of A(H1)pdm09 viruses has been detected in patients in intensive care units (ICUs) (1308 out of 1527 subtyped: 86%) than in other hospitalized patients (961 out of 1520 subtyped: 63%).

    5 countries reported a total of 384 fatal cases: 381 (99%) were associated with influenza virus type A infection and 3 (1%) with type B. Of 280 influenza A viruses subtyped from fatal cases, 227 (81%) were A(H1)pdm09 and 53 (19%) were A(H3).

    The results from SARI surveillance at sentinel hospitals reported to the WHO Regional Office for Europe (EuroFlu) and hospitalized laboratory-confirmed influenza cases reported to the European Centre for Disease Prevention and Control (ECDC) differ in that the former include a higher proportion of influenza A(H3N2) and a lower proportion of influenza A(H1N1)pdm09 than the latter. This pattern is most likely due to the circulation of the different influenza virus subtypes in countries.

    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 reported by countries on RSV, detections peaked in week 50/2013 and have decreased in all the reporting countries since. This represents a slightly later start than in the previous season (see Country data and graphs for 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 data for 14/2014 showed that all-cause mortality was within the normal range for all reporting countries. 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.

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