[Source: EuroFlu, full page: (LINK). Edited.]
EuroFlu - Weekly Electronic Bulletin - Week 11 : 11/03/2013-17/03/2013 - 22 March 2013, Issue No. 480
Influenza activity continues to increase in some eastern countries while decreasing in many other European countries
Summary, week 11/2013
- During week 11/2013, consultation rates for influenza-like illness (ILI) and/or acute respiratory infection (ARI) continued to decline throughout most parts of the WHO European Region, with most countries reporting medium activity.
- A few countries in the east, however, reported increasing clinical outpatient activity.
- The percentage of sentinel specimens testing positive for influenza has started to decline overall, but remains high in several countries.
- While pandemic influenza A(H1N1)pdm09 and influenza B co-dominate in northern and western Europe, A(H1N1)pdm09 is the dominant virus in the central and eastern parts of the Region.
- The number of hospitalizations due to severe acute respiratory infection (SARI) decreased slightly in week 11/2013, but some eastern countries reported increased influenza-positivity rates among SARI cases, in line with increases in ARI/ILI consultation rates.
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 11/2013 a total of 4821 specimens tested positive for influenza, with 2783 (58%) positive for influenza A (Fig. 1). The proportion of influenza A viruses has continued to decrease 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 1639 subtyped, 1016 (62%) were A(H1N1)pdm09 and 623 (38%) were A(H3N2) (Fig. 2a).
Since the beginning of the season (week 40/2012), 78 182 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, 51 113 (65%) were influenza A and 27 069 (35%) influenza B (Fig. 2b).
Of the 32 806 influenza A viruses that have been subtyped, 23 002 (70%) were A(H1N1)pdm09 and 9 804 (30%) were A(H3N2).
In addition, the lineage for 4065 influenza B viruses has been determined: 3720 (92%) belonged to the B/Yamagata lineage and 345 (8%) to B/Victoria.
Circulation of influenza viruses in week 11/2013 remained diverse across the Region, with more northern and western countries reporting the dominance of influenza B or co-circulation of influenza A and B. Influenza A was reported as the dominant virus mainly by countries in eastern and central Europe, as well as in Greece, Ireland and the United Kingdom (England, Wales and Northern Ireland) (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, 4099 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 (30%).
Scotland reported on 495 (35%) 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 1101 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 967 viruses for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir.
Of the 442 A(H1N1)pdm09 viruses tested, 433 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 233 influenza A(H3N2) viruses tested showed susceptibility to both drugs.
Of the 292 influenza B viruses tested, 291 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 44 influenza A(H1N1)pdm09 and 19 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)
A few countries, mainly in the eastern part of the Region, reported increasing influenza activity for week 11/2013 (Map 4). In week 11/2013, only 1 (Bosnia and Herzegovina) reported high intensity, in contrast to 4 countries during week 10/2013 (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, 4 (the Czech Republic, France, Israel and Kazakhstan) reported ILI/ARI consultation rates below their national threshold levels.
The percentage of sentinel specimens testing positive for influenza has decreased in comparison with week 10/2013; 1571 sentinel specimens were tested of which 634 (40%) were positive for influenza (Fig. 5).
In the 20 countries testing 20 or more sentinel specimens, influenza positivity ranged from 11% to 76%, with a median of 42% (mean: 43%).
Of the 634 influenza-positive specimens from sentinel sources, 59% were positive for influenza B.
The proportion of sentinel samples testing positive for influenza B has gradually increased since week 03/2013 (Fig. 6a). As in the two previous weeks, most of these detections were reported by 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 11/2013 the number of SARI hospitalizations decreased in comparison with previous weeks, but remained above pre-season levels (Fig. 7). This trend indicates that SARI hospitalization has peaked for the season in Belgium, Kyrgyzstan and Slovakia, concurrently with overall declines in outpatient ILI or ARI consultation rates.
During week 11/2013 Armenia, Georgia, the Russian Federation and Ukraine showed increases in cases in the groups aged 30–64 and/or ≥65 years, coinciding with increased influenza-positivity rates and concurrent with increases in ARI/ILI 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 11/2013, 13 countries (Albania, Armenia, Belarus, Belgium, Georgia, Kazakhstan, Kyrgyzstan, the Republic of Moldova, Romania, the Russian Federation, Serbia, Slovakia and Ukraine) reported 130 influenza detections among 356 specimens tested, 65% of which were influenza A (Fig. 8a).
As in week 10/2013, most of the detections were reported by 5 countries (Armenia, Georgia, Romania, the Russian Federation and Ukraine). Since week 40/2012, 5731 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), 111 such cases were reported for week 11/2013. 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).
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 11/2013 data, based on 16 countries or regions, showed a pattern similar to those in the previous weeks, with excess mortality among people aged ≥65 years. This pattern started in week 01/2013 and continues. Mortality in the most recent weeks may be overestimated, however, because of imprecise adjustment of delayed registrations.
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)