[Source: EuroFlu, full page: (LINK). Edited.]
EuroFlu - Weekly Electronic Bulletin - Week 8 : 18/02/2013-24/02/2013 - 01 March 2013, Issue No. 477
Influenza activity still high in central and eastern Europe but declining in western countries
Summary, week 8/2013
- Consultation rates for influenza-like illness (ILI) and/or acute respiratory infection (ARI) have continued to increase in the central and eastern parts of the WHO European Region, but started to decrease in some northern and western countries.
- In countries such as Ireland, the Netherlands and the United Kingdom, ILI rates have returned to lower levels but remain above the epidemic threshold.
- Influenza A(H1N1)pdm09, A(H3N2) and type B viruses continued to co-circulate in the Region.
- A(H1N1)pdm09 predominates, including in patients hospitalized for severe acute respiratory infection (SARI), mainly in the eastern part of the Region, where the number of SARI cases has increased slowly in association with increasing influenza activity.
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 08/2013, a total of 6706 specimens tested positive for influenza, with 4311 (64%) being influenza A (Fig. 1).
Influenza A(H1N1)pdm09 viruses remained the dominant A virus: of 2887 subtyped, 2136 (74%) were A(H1N1)pdm09 and 751 (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), 55 647 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, 37 724 (68%) were influenza A and 17 923 (32%) influenza B (Fig. 2b).
Of the 24 233 influenza A viruses that have been subtyped, 17 556 (72%) were A(H1N1)pdm09 and 6 677 (28%) were A(H3N2).
In addition, the lineages for 2278 influenza B viruses were determined: 2078 (91%) belonged to the B/Yamagata lineage and 200 (9%) to B/Victoria.
Circulation of influenza viruses in week 08/2013 varied by country.
Influenza A, mainly A(H1N1)pdm09, was reported as the dominant virus in countries in eastern and central Europe, while influenza B was reported as the dominant virus in some countries in the southern part of the Region (Map 1). Between these areas, a number of countries reported co-circulation of influenza A and 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).
For the composition of influenza virus vaccines for the northern hemisphere 2013–2014, on 20 February, WHO expert group recommended updates of the A(H3N2) and B/Yamagata lineage components (see the WHO headquarters web site).
An update of the A(H3N2) vaccine component was recommended because of antigenic changes in earlier A/Victoria/361/2011-like vaccine viruses resulting from adaptation to propagation in eggs. It was recommended that the cell-propagated A/Victoria/361/2011-like vaccine virus be A/Texas/50/2012, as it showed limited antigenic change on egg-adaptation. 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, 2493 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 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 (1111: 45%).
Scotland reported on 492 (47%) of the 1037 A/Victoria/361/2011 (H3N2)-like viruses characterized this season.
14 countries (Austria, Belgium, Denmark, Finland, Germany, Greece, Ireland, Italy, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom (Scotland)) have characterized 723 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, 11 countries (Denmark, Germany, Greece, the Netherlands, Norway, Portugal, the Russian Federation, Spain, Sweden, Switzerland and the United Kingdom) have screened 422 viruses for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir.
Of the 198 A(H1N1)pdm09 viruses tested, 195 showed susceptibility to both drugs, 3 viruses carrying the neuraminidase H275Y amino acid substitution, causing resistance to oseltamivir, were detected in the Netherlands (2) and Switzerland (1) in hospitalized immunocompromised patients exposed to oseltamivir through treatment.
The 126 influenza A(H3N2) and 98 influenza B viruses tested showed susceptibility to both drugs. The 31 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)
Countries located mainly in the western part of the Region reported decreasing influenza activity for week 08/2013 (Map 4), but most continued to report medium intensity levels (Map 2) and widespread circulation of influenza (Map 3). Of the countries that have established epidemic thresholds, all reported ILI/ARI consultation rates above their national threshold levels.
In week 08/2013, 2586 sentinel specimens were tested of which 1230 (48%) were positive for influenza, similar to week 07/2013 (Fig. 5).
In the 31 countries testing 20 or more sentinel specimens, influenza positivity ranged from 14% to 75%, with a median of 49% (mean: 44%).
Of the 1230 influenza-positive specimens from sentinel sources, 49% were positive for influenza B, similar to week 07/2013 (Fig. 6a). Most of the influenza B detections were reported by France, Italy 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
The weekly number of SARI hospitalizations may have peaked for the season for Belgium and Romania, and is levelling off in Belarus, Kazakhstan and Ukraine.
An increase in SARI cases from week 07 to week 08 was observed in Armenia, Georgia and the Russian Federation.
The proportion of respiratory specimens from patients with SARI that tested positive for influenza remained relatively stable over the last 2 weeks (Fig. 7).
For several weeks, coinciding with increased positivity rates and the predominance of A(H1N1)pdm09, 5 countries (Belarus, Belgium, Georgia, Romania and Serbia) showed increases in cases in the groups aged 30–64 and/or ≥65 years, while increases in cases in the group aged 15–29 were observed in Ukraine.
Since the beginning of the season, the increase in SARI cases testing positive for influenza in Belgium, Georgia, Kazakhstan, Romania and Ukraine has been more or less in line with the increase in the reported number of SARI hospitalizations.
For week 08/2013, 12 countries (Armenia, Belarus, Belgium, Georgia, Kazakhstan, Kyrgyzstan, the Republic of Moldova, Romania, the Russian Federation, Serbia, Slovakia and Ukraine) reported 165 influenza detections among 459 specimens tested, 79% 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 gradually increased, with influenza A(H1N1)pdm09 predominant.
Since week 40/2012, 4253 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), 111 such cases were reported for week 08/2013. 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 data presented by countries reporting on RSV, the positivity rate in countries in western Europe peaked around week 52/2012 (see Country data and graphsfor individual country data). RSV detections were still high in week 08/2013, however, in countries such as Latvia, Poland and Sweden.
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 08/2013 data, based on 15 countries or regions, showed similar excess mortality patterns to last week’s: all-cause mortality among people aged 65 and older was around 3 z-scores above the baseline in weeks 01–03, and has been around 4 z-scores since week 04/2013. No excess mortality in younger age groups has been detected so far this season. Results of pooled analysis may vary, depending on which countries are included in the weekly analysis.
Individual country analysis showed a diverse temporal pattern of all-cause mortality in people aged ≥65 years. While mortality increases to around 3 z-scores above the baseline were seen at the end of 2012 in some countries (Denmark, Ireland, Sweden and the United Kingdom (England and Scotland)), these increases started later in others (France, the Netherlands).
In some countries (Belgium, Finland and Switzerland) mortality increased only moderately (around 2 z scores above the baseline), while others (Germany (Berlin, Hesse), Hungary, Portugal and Spain) have not yet had any mortality increases.
The highest and longest sustained excess mortality was seen in Denmark, where influenza activity was dominated by A(H3N2) circulation (excess mortality from week 51/2012 to week 06/2013, with peak values of 7 z-scores in week 01 and 5 z-scores in week 05).
The diverse mortality pattern may be explained by the pattern of influenza activity this season in Europe, but other factors, such as extreme cold, may have played a role. 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)
Republic of Moldova: This week 57 samples were tested for Influenza viruses, of which 18 were positive for RNA influenza virus A(H1N1)pdm09; 3 samples, positive for RNA influenza virus A(H3N2); and 10, for RNA influenza virus type B.