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EuroFlu - Weekly Electronic Bulletin - Week 17 : 22/04/2013-28/04/2013 - 03 May 2013, Issue No. 486: Influenza season ending in Europe
[Source: EuroFlu, full page: (LINK). Extract, edited.]
EuroFlu - Weekly Electronic Bulletin - Week 17 : 22/04/2013-28/04/2013 - 03 May 2013, Issue No. 486
Influenza season ending in Europe
Summary, week 17/2013
For a description of influenza surveillance in the WHO European Region see below.
Virological surveillance for influenza
During week 17/2013, 382 specimens tested positive for influenza, with 236 (62%) positive for influenza B, similarly to the previous three weeks (Fig. 1).
Among total weekly influenza detections (sentinel and non-sentinel), the proportion of influenza A viruses in relation to influenza B has gradually decreased since week 03/2013, when type A viruses represented 76% of the total.
Of the 45 influenza A viruses that were subtyped during week 17/2013, 13 (29%) were influenza A(H1N1)pdm09 and 32 (71%) influenza A(H3N2) (Fig. 2a).
Since the beginning of the season (week 40/2012), 94 358 influenza viruses from sentinel and non-sentinel sources have been detected and typed.
Cumulatively, 59 270 viruses (63%) were influenza A and 35 088 (37%) influenza B (Fig. 2b).
Cumulatively, influenza A has been the most commonly detected virus since week 47/2012.
Of the 38 106 influenza A viruses that have been subtyped, 25 433 (67%) were A(H1N1)pdm09 and 12 673 (33%) were A(H3N2).
In addition, the lineage for 5732 influenza B viruses has been determined: 5254 (92%) belonged to the B/Yamagata lineage and 478 (8%) to B/Victoria.
(?)
Owing to the low number of viruses detected during week 17/2013 in most countries, only a few reported on dominant virus type: influenza B in Bulgaria, Georgia, Germany, Greece, Latvia, Slovenia and the United Kingdom (Scotland), and influenza A in Estonia, Ireland and the United Kingdom (Wales) (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, 5300 influenza viruses characterized antigenically by 17 countries (Austria, Bulgaria, the Czech Republic, Denmark, Germany, Greece, Italy, Latvia, Portugal, the Republic of Moldova, 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 1408 of these viruses (27%). Scotland reported on 500 (32%) of the 1541 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 1574 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 1394 viruses for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir.
Of the 695 A(H1N1)pdm09 viruses tested, 682 showed susceptibility to both drugs while 13 viruses (2%) carried the neuraminidase H275Y amino acid substitution, causing resistance to oseltamivir.
Of these 13 viruses, 1 from the Russian Federation was detected in a hospitalized patient not exposed to oseltamivir through treatment; 1 from Germany was detected in a hospitalized patient with unknown exposure to the neuraminidase inhibitors; 2 viruses from the United Kingdom were detected in outpatients not exposed to oseltamivir through treatment; 6 viruses were detected in hospitalized patients exposed to oseltamivir through treatment (1 from Denmark, 4 from Germany and 1 from Sweden) and 3 viruses were detected in hospitalized immunocompromised patients exposed to oseltamivir through treatment (2 from the Netherlands and 1 from Switzerland).
The 294 influenza A(H3N2) viruses tested showed susceptibility to both drugs.
Of the 405 influenza B viruses tested, 404 showed susceptibility to both drugs; 1 virus, showing reduced inhibition by oseltamivir and normal inhibition by 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 105 influenza A(H1N1)pdm09 and 50 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)
Similarly to several previous weeks, most countries in the Region reported decreasing influenza activity (Map 4), low intensity (Map 2) and no or sporadic influenza activity in week 17/2013 (Map 3).
Of the 20 countries that have established epidemic thresholds, all reported ILI/ARI consultation rates below their national threshold levels.
(?)
In week 17/2013 the percentage of sentinel specimens testing positive for influenza decreased notably from that in the previous week: 225 sentinel specimens were tested, of which 23 (10%) were positive for influenza (Fig. 5). This decreasing trend has continued since the peak for the season, around week 07/2013.
In the 4 countries testing 20 or more sentinel specimens, influenza positivity ranged from 0% to 19%, with a median of 11% (mean: 10%).
Of the 23 influenza-positive specimens from sentinel sources, 78% were positive for influenza B. Influenza B has been prevalent for several weeks in countries where circulation of A(H1N1)pdm09 has decreased. 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 17/2013 the number of SARI hospitalizations, along with the influenza positivity rate among cases, returned to pre-season levels in most of the countries taking part in hospital surveillance for SARI (Fig. 7).
This decreasing trend indicates that cases have peaked for the season for all the countries taking part in hospital surveillance for SARI.
For week 17/2013, only 8 countries (Armenia, Belarus, Georgia, Kazakhstan, Kyrgyzstan, Romania, Slovakia and Ukraine) reported 20 influenza detections among 93 specimens tested, 95% of which were influenza B, in line with the detections reported from outpatient surveillance (Fig. 8a). Armenia reported most of the detections. Since week 40/2012, 7076 SARI specimens have been collected and tested for influenza.
Click here for a detailed overview in table format.
(?)
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).
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 17/2013, based on 13 countries or regions, showed a sustained peak of excess all-cause mortality among those aged 65 years and over.
Excess mortality started in week 01/2013, peaked in week 10/2013 and has since declined, but has not yet returned to normal levels.
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.
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EuroFlu - Weekly Electronic Bulletin - Week 17 : 22/04/2013-28/04/2013 - 03 May 2013, Issue No. 486
Influenza season ending in Europe
Summary, week 17/2013
- Influenza-like illness (ILI) and acute respiratory infection (ARI) consultation rates are low throughout the WHO European Region.
- The great majority of countries report no or sporadic influenza activity.
- The percentages of sentinel ILI, ARI and severe acute respiratory infection (SARI) specimens testing positive for influenza have declined in recent weeks.
- Influenza B is becoming the dominant virus in circulation, followed by influenza A(H3N2), with relatively few A(H1N1)pdm09 viruses.
- For information about human infections with avian influenza A(H7N9) virus in China please click here. [Borken URL, md.]
For a description of influenza surveillance in the WHO European Region see below.
Virological surveillance for influenza
During week 17/2013, 382 specimens tested positive for influenza, with 236 (62%) positive for influenza B, similarly to the previous three weeks (Fig. 1).
Among total weekly influenza detections (sentinel and non-sentinel), the proportion of influenza A viruses in relation to influenza B has gradually decreased since week 03/2013, when type A viruses represented 76% of the total.
Since the beginning of the season (week 40/2012), 94 358 influenza viruses from sentinel and non-sentinel sources have been detected and typed.
Cumulatively, 59 270 viruses (63%) were influenza A and 35 088 (37%) influenza B (Fig. 2b).
Cumulatively, influenza A has been the most commonly detected virus since week 47/2012.
Of the 38 106 influenza A viruses that have been subtyped, 25 433 (67%) were A(H1N1)pdm09 and 12 673 (33%) were A(H3N2).
In addition, the lineage for 5732 influenza B viruses has been determined: 5254 (92%) belonged to the B/Yamagata lineage and 478 (8%) to B/Victoria.
(?)
Owing to the low number of viruses detected during week 17/2013 in most countries, only a few reported on dominant virus type: influenza B in Bulgaria, Georgia, Germany, Greece, Latvia, Slovenia and the United Kingdom (Scotland), and influenza A in Estonia, Ireland and the United Kingdom (Wales) (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, 5300 influenza viruses characterized antigenically by 17 countries (Austria, Bulgaria, the Czech Republic, Denmark, Germany, Greece, Italy, Latvia, Portugal, the Republic of Moldova, 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 1408 of these viruses (27%). Scotland reported on 500 (32%) of the 1541 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 1574 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 1394 viruses for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir.
Of the 695 A(H1N1)pdm09 viruses tested, 682 showed susceptibility to both drugs while 13 viruses (2%) carried the neuraminidase H275Y amino acid substitution, causing resistance to oseltamivir.
Of these 13 viruses, 1 from the Russian Federation was detected in a hospitalized patient not exposed to oseltamivir through treatment; 1 from Germany was detected in a hospitalized patient with unknown exposure to the neuraminidase inhibitors; 2 viruses from the United Kingdom were detected in outpatients not exposed to oseltamivir through treatment; 6 viruses were detected in hospitalized patients exposed to oseltamivir through treatment (1 from Denmark, 4 from Germany and 1 from Sweden) and 3 viruses were detected in hospitalized immunocompromised patients exposed to oseltamivir through treatment (2 from the Netherlands and 1 from Switzerland).
The 294 influenza A(H3N2) viruses tested showed susceptibility to both drugs.
Of the 405 influenza B viruses tested, 404 showed susceptibility to both drugs; 1 virus, showing reduced inhibition by oseltamivir and normal inhibition by 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 105 influenza A(H1N1)pdm09 and 50 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)
Similarly to several previous weeks, most countries in the Region reported decreasing influenza activity (Map 4), low intensity (Map 2) and no or sporadic influenza activity in week 17/2013 (Map 3).
Of the 20 countries that have established epidemic thresholds, all reported ILI/ARI consultation rates below their national threshold levels.
(?)
In week 17/2013 the percentage of sentinel specimens testing positive for influenza decreased notably from that in the previous week: 225 sentinel specimens were tested, of which 23 (10%) were positive for influenza (Fig. 5). This decreasing trend has continued since the peak for the season, around week 07/2013.
In the 4 countries testing 20 or more sentinel specimens, influenza positivity ranged from 0% to 19%, with a median of 11% (mean: 10%).
(?)
Hospital surveillance for SARI
In week 17/2013 the number of SARI hospitalizations, along with the influenza positivity rate among cases, returned to pre-season levels in most of the countries taking part in hospital surveillance for SARI (Fig. 7).
This decreasing trend indicates that cases have peaked for the season for all the countries taking part in hospital surveillance for SARI.
Click here for a detailed overview in table format.
(?)
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).
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 17/2013, based on 13 countries or regions, showed a sustained peak of excess all-cause mortality among those aged 65 years and over.
Excess mortality started in week 01/2013, peaked in week 10/2013 and has since declined, but has not yet returned to normal levels.
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.
(?)
-
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