25 Jan 2013

EuroFlu - Weekly Electronic Bulletin - Week 3 : 14/01/2013-20/01/2013 - 25 January 2013, Issue No. 472 (edited)

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

EuroFlu - Weekly Electronic Bulletin - Week 3 : 14/01/2013-20/01/2013 - 25 January 2013, Issue No. 472

The patterns of influenza activity remain diverse across the WHO European Region

 

Summary, week 3/2013

  • Consultation rates for influenza-like illness (ILI) and/or acute respiratory infection (ARI) are increasing in the majority of countries in the Region, including eastern Europe, but have started to decrease in northern countries.
  • Influenza A(H1N1)pdm09, A(H3N2) and type B viruses are circulating in the Region, but the relative proportion of influenza A(H1N1)pdm09 in samples from sentinel and non-sentinel sources continues to increase.
  • The number of reported hospitalizations due to severe acute respiratory infection (SARI) is increasing slowly in association with the increase in influenza activity in the eastern part of the Region.

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

The number of specimens testing positive for influenza in the Region was similar to the previous week, again mainly due to detections in the western part of the Region. Overall, a total of 3741 specimens tested positive for influenza in week 3/2013, which 2840 (76%) were influenza A (Fig. 1).

For week 3/2013 the picture related to the proportion of influenza A(H1N1)pdm09 viruses versus A(H3N2) was similar to those in the two previous weeks, with A(H1N1)pdm09 dominating: of 1856 influenza A viruses subtyped, 1488 (80%) were A(H1N1)pdm09 while 368 (20%) were A(H3N2) (Fig. 2a).

Since the beginning of the season (week 40/2012), 16 457 influenza viruses from sentinel and non-sentinel sources have been typed: 11 318 (69%) were influenza A and 5 139 (31%) influenza B (Fig. 2b).

Of the influenza A viruses, 6698 were subtyped: 4552 (68%) as A(H1N1)pdm09 and 2146 (32%) as A(H3N2).

In addition, since week 40/2012, the lineage for 788 influenza B viruses has been determined: 707 (90%) belonged to the B/Yamagata lineage and 81 (10%) to B/Victoria.

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The circulation of influenza viruses remains variable across the Region.

Influenza A (mainly A(H1N1)pdm09) continues to be reported as the dominant virus in an increasing number of countries in northern and central Europe, the Russian Federation and Turkey, while influenza B is reported as the dominant virus in some countries in the southern and western parts of the Region (Map 1).

Between these areas, co-circulation of A(H1N1)pdm09, A(H3N2) and influenza B is reported.

 

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 web site). The majority of characterized viruses from the WHO European Region have been similar to these vaccine viruses.

Since week 40/2012, 964 influenza viruses characterized antigenically by 10 countries (Denmark, the United Kingdom (England), Germany, Latvia, Portugal, Romania, the Russian Federation, Scotland, Slovakia, Switzerland) corresponded with the viruses recommended by WHO for inclusion in the current northern hemisphere seasonal influenza vaccine (Fig. 3). 11 countries (Austria, Belgium, Denmark, Finland, Germany, Norway, Portugal, Scotland, Spain, Sweden, Switzerland) have characterized 240 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.

At present, both A(H1N1)pdm09 and A(H3N2) viruses fall into a number of different genetic groups, but they remain antigenically similar to their respective vaccine viruses, A/California/7/2009 and A/Victoria/361/2011.

Influenza B viruses of the B/Victoria/2/87 and the B/Yamagata/16/88 lineages are co-circulating with the clear dominance of the B/Yamagata lineage viruses this season.

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 in circulation clearly fall into two distinct genetic clades, 2 and 3 represented by B/Estonia/55669/2011 and B/Wisconsin/1/2010 respectively. Viruses in these clades can be distinguished antigenically from each other, but the antigenic differentiation of these clades is not clear-cut as post-infection ferret antisera raised against clade 2 viruses are more clade-specific than are antisera raised against clade 3 viruses. Nevertheless, viruses within these clades remain antigenically similar to the current vaccine strain.

 

Monitoring of susceptibility to antiviral drugs

Since week 40/2012, 7 countries (Denmark, Germany, the Netherlands, Norway, Spain, Sweden and the United Kingdom) have screened 196 viruses for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir.

The 78 influenza A(H3N2), 52 A(H1N1)pdm09 and 66 influenza B viruses showed susceptibility to both drugs.

The 14 influenza A(H3N2) and 5 influenza A(H1N1)pdm09 viruses screened for susceptibility to adamantanes were found to be resistant.

 

Outpatient surveillance for influenza-like illness (ILI) and/or acute respiratory infection (ARI)

ILI and ARI consultation rates continue to increase in the eastern part of the Region (Map 4), but with mainly low intensity levels across this area (Map 2); only Kazakhstan reported medium intensity. In contrast, consultation rates for ILI and ARI started to decrease in northern European countries (Map 4) despite a high proportion of specimens testing positive for influenza (see Country data and graphs for individual country data). A higher number of countries in the central part of the Region reported regional or widespread circulation of influenza in week 3/2013 (Map 3).

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The number of specimens tested from sentinel outpatient clinics is increasing, notably in France, Germany, Poland, Spain, Turkey and the United Kingdom. Overall, 2286 specimens were tested, of which 909 (40%) were positive for influenza in week 3/2013, similar to the proportions in the previous 2 weeks (Fig. 5).

Of the 909 positive specimens from sentinel sources, influenza A was detected in 62% (Fig. 6), a slight increase from the 2 previous weeks. 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 number of hospitalizations due to SARI continues to rise, with a similar proportion of respiratory specimens from patients testing positive for influenza (Fig. 7). Overall, most reporting countries, except Belgium and Slovakia, reported cases mainly in the group aged 0–4 years (see Country data and graphsfor individual country data).

The increase in numbers of SARI cases testing positive for influenza (Fig. 7), is in line with increasing influenza activity in countries reporting on SARI hospitalizations. In week 3/2013, 9 countries (Belarus, Belgium, Georgia, Kyrgyzstan, Romania, the Russian Federation, Serbia, Slovakia and Ukraine) detected a total of 27 influenza viruses among 237 specimens tested (Fig. 8). Since week 40/2012, 2272 SARI specimens have been collected and tested for influenza. Click here for a detailed overview in table format.

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Among the countries reporting on hospitalization of severe influenza cases to the European Centre for Disease Prevention and Control (ECDC), 30 such cases were reported for week 3/2013. This reflects the higher levels of influenza activity in the western part of the Region. 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.

 

The EUROMOMO mortality monitoring system

EuroMOMO is a project aimed 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 EU countries. Pooled analysis as of week 3/2013 shows no excess all-cause mortality as yet this season.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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Country comments (where available)

  • Czech Republic: Up to end of week 3/2013 a cumulative total of 140 severe influenza patients with laboratory-confirmed influenza were reported by intensive and resuscitation care units including 24 deaths.
  • Republic of Moldova: This 3rd sentinel week in one sentinel sample was detected ARN Influenza type B and in one non-sentinel sample was detected ARN Influenza virus A(H1N1)pdm.

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