EuroFlu - Weekly Electronic Bulletin
Week 18 : 29/04/2013-05/05/2013 10 May 2013, Issue No. 487     

Influenza activity is at out-of-season levels in Europe

Summary, week 18/2013

Consultation rates for influenza-like illness (ILI) and acute respiratory infection (ARI) are at low levels in all countries. The percentages of sentinel samples from ILI, ARI, and severe acute respiratory infection (SARI) surveillance that tested positive for influenza were low. Influenza B was detected in most of the positive specimens collected in week 18/2013, although most virus detections since the start of the season have been influenza A. Countries with hospital-based sentinel surveillance continue to report SARI hospitalizations, although numbers are declining overall, as is the proportion of samples testing positive for influenza. For information about human infections with avian influenza A(H7N9) virus in China please click here.

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 18/2013, 342 specimens tested positive for influenza, with 224 (66%) positive for influenza B, similar to the previous three weeks (Fig. 1). For 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 48 influenza A viruses that were subtyped during week 18/2013, 16 (33%) were influenza A(H1N1)pdm09 and 32 (67%) influenza A(H3N2) (Fig. 2a). Since the beginning of the season (week 40/2012), 95 070 influenza viruses from sentinel and non-sentinel sources have been detected and typed. Cumulatively, 59 534 viruses (63%) were influenza A and 35 536 (37%) influenza B (Fig. 2b). Cumulatively, influenza A has been the most commonly detected virus since week 47/2012. Of the 38 292 influenza A viruses that have been subtyped, 25 492 (67%) were A(H1N1)pdm09 and 12 800 (33%) were A(H3N2).

In addition, the lineage for 5822 influenza B viruses has been determined: 5341 (92%) belonged to the B/Yamagata lineage and 481 (8%) to B/Victoria.

Click to expand

Owing to the low number of viruses detected during week 18/2013 in most countries, only a few reported on dominant virus type: influenza B in Georgia, Germany, Latvia, Lithuania and the Russian Federation, and influenza A in Finland, Greece and the United Kingdom (England and Wales); the United Kingdom (Scotland) reported co-dominance of influenza A and B (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, 5467 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 1420 of these viruses (26%). Scotland reported on 499 (32%) of the 1583 A/Victoria/361/2011 (H3N2)-like viruses characterized this season. 16 countries (Austria, Belgium, Denmark, Finland, Germany, Greece, Ireland, Italy, the Netherlands, Norway, Portugal, the Russian Federation, Spain, Sweden, Switzerland and the United Kingdom (Scotland)) have characterized 1642 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 1400 viruses for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir. Of the 697 A(H1N1)pdm09 viruses tested, 684 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 296 influenza A(H3N2) viruses tested showed susceptibility to both drugs. Of the 407 influenza B viruses tested, 406 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)

During week 18/2013, all countries but 1 reported low influenza activity (Map 2). Most countries in the Region reported decreasing trends (Map 4) and no or sporadic influenza activity in week 18/2013 (Map 3).

ILI and ARI consultation rates were below the national baselines or at pre-season levels in all countries reporting clinical data during week 18/2013.

Click to expand Click to expand Click to expand

Click on the maps for more detailed information.

For week 18/2013, the percentage of sentinel specimens testing positive for influenza remained low: 197 sentinel specimens were tested, of which 21 (11%) 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 9%, with a median of 7% (mean: 6%).

Of the 21 influenza-positive specimens from sentinel sources, 81% 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 18/2013 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).

For week 18/2013, only 4 countries (Armenia, Belarus, Georgia and Kyrgyzstan) reported a total of 5 influenza detections all of which were influenza B, in line with the detections reported from outpatient surveillance (Fig. 8a). Since week 40/2012, 7188 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), 2 such cases were reported for weeks 17–18 /2013. 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).

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.

Table 1. Influenza virus detections in sentinel specimens
Specimens tested
and viruses
Current week
(number and %)
Cumulative since week 40
(number and %)
Specimens tested 197 48 45093 7188
    Influenza A + B 21 (10.7%) 5 (10.4%) 18087 (40.1%) 1961 (27.3%)
        Influenza A 4 (19.1%) 0 (0.0%) 8951 (49.5%) 1246 (63.5%)
        Influenza B 17 (81.0%) 5 (100.0%) 9136 (50.5%) 715 (36.5%)
    Influenza A subtyped   2 0 8127 1151
        A (H1N1)pdm09 2 (100.0%) 0 (0.0%) 5084 (62.6%) 767 (66.6%)
        A (H3N2) 0 (0.0%) 0 (0.0%) 3043 (37.4%) 383 (33.3%)


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Northern Ireland Iceland Denmark Norway Norway Sweden Sweden Denmark Scotland Scotland Finland Sweden England England England England Wales Ireland The Netherlands Belgium France France Switzerland Germany Germany Bulgaria Czech Republic Slovakia Slovenia Poland Poland Hungary France Italy Italy Italy Italy Italy Spain Spain Spain Spain Spain Portugal Portugal (Azores) Greece Estonia Albania FYROM Turkey Turkey Finland Finland Finland Romania Romania Malta Cyprus Austria Croatia Boznia and Herzegovina Montenegro Serbia Lithuania Luxembourg Latvia Denmark Norway
Country comments (where available)

  Republic of Moldova
This week, 7 samples were tested for Influenza viruses, of which 1 was positive for RNA influenza virus B.
Table and graphs

Intensity Geographic
Trend Dominant
swabs (% pos.)
ILI per
100 000
ARI per
100 000
Virology graph
and pie chart
ArmeniaLowNoneDecreasingNone0(-)78.4 (graphs)
Click here
AustriaLowLocalStableNone0(-)0.0 (graphs)Click here
AzerbaijanLowSporadicDecreasingNone15(6.7%)160.2 (graphs)Click here
BelarusLowSporadicDecreasingNone21(4.8%)9.6 (graphs)759.6 (graphs)
Click here
BelgiumLowNoneStableNone0(-)11.0 (graphs)1229.9 (graphs)
Click here
Bosnia and HerzegovinaMediumRegionalDecreasingNone4.1 (graphs)Click here
BulgariaLowSporadicDecreasingNone0(-)197.9 (graphs)Click here
CroatiaLowSporadicDecreasingNone2.4 (graphs)Click here
CyprusLowNoneStable0.4 * (graphs)6.1 * (graphs)Click here
DenmarkLowNoneStable12.3 (graphs)Click here
EstoniaLowSporadicDecreasingNone1(0%)6.7 (graphs)228.9 (graphs)Click here
FinlandLowNoneStableType A, Subtype H19(11.1%) (graphs)Click here
GeorgiaLowSporadicDecreasingType B12(83.3%)178.7 (graphs)
Click here
GermanyLowSporadicDecreasingType B19(10.5%)691.1 (graphs)Click here
GreeceLowSporadicDecreasingType A, Subtype pH1N10(-)25.4 (graphs)Click here
HungaryLowNoneDecreasingNone3(0%)14.7 (graphs)Click here
Iceland0(-) (graphs)Click here
IrelandLowSporadicDecreasingNone6(0%)4.8 (graphs)Click here
IsraelLowNoneStable4.0 (graphs)Click here
KazakhstanLowSporadicDecreasingNone7(0%)3.7 (graphs)68.5 (graphs)
Click here
KyrgyzstanNone2(0%)18.9 (graphs)26.6 (graphs)
Click here
LatviaLowSporadicDecreasingType B0(-)5.2 (graphs)714.2 (graphs)Click here
LithuaniaLowLocalDecreasingType B1(100.0%)2.0 (graphs)361.2 (graphs)Click here
LuxembourgLowNone2(0%)0.4 * (graphs)11.0 * (graphs)Click here
MaltaNone0(-) (graphs)Click here
MontenegroLowNoneDecreasing3.9 (graphs)Click here
NetherlandsLowSporadicStableNone1(0%)24.1 (graphs)Click here
NorwayLowLocalStableType B0(-)17.6 (graphs)Click here
PolandLowNoneDecreasingNone0(-)72.6 (graphs)Click here
PortugalLowSporadicStableNone1(0%)0.0 (graphs)Click here
Republic of MoldovaLowSporadicDecreasingNone5(0%) (graphs)113.4 (graphs)
Click here
RomaniaLowSporadicDecreasingNone0-0.5 (graphs)319.8 (graphs)
Click here
Russian FederationLowSporadicDecreasingType B22(0%)0.2 (graphs)320.7 (graphs)
Click here
SerbiaLowNoneDecreasing8.6 (graphs)
Click here
SlovakiaLowSporadicDecreasingNone0(-)73.7 (graphs)1074.6 (graphs)
Click here
SloveniaLowSporadicDecreasingNone0(-)1.5 (graphs)495.8 (graphs)Click here
SpainLowSporadicStableNone22(9.1%)5.0 (graphs)Click here
SwedenLowSporadicDecreasingNone2(0%)1.6 (graphs)Click here
SwitzerlandLowNoneStable3.8 (graphs)Click here
The former Yugoslav Republic of MacedoniaLowSporadicDecreasingNone0(-)1.6 (graphs)Click here
TurkeyLowSporadicDecreasingNone5(0%)64.3 (graphs)Click here
United Kingdom - EnglandLowLocalDecreasingType A11(0%)3.9 (graphs)254.0 (graphs)Click here
United Kingdom - Northern IrelandLowLocalDecreasingNone5(0%)13.7 (graphs)328.4 (graphs)Click here
United Kingdom - ScotlandLowLocalDecreasingType A and B20(15.0%)9.6 (graphs)369.6 (graphs)Click here
United Kingdom - WalesLowNoneDecreasingType A, Subtype H30(-)2.2 (graphs)Click here
UkraineLowNoneDecreasingNone4(0%)1.8 * (graphs)250.1 (graphs)
Click here
UzbekistanLowNoneDecreasingNone1(0%) (graphs)18.3 (graphs)Click here
Europe197(10.7%) Click here
Preliminary data

Intensity: Low = no influenza activity or influenza activity at baseline level; Medium = usual levels of influenza activity; High = higher than usual levels of influenza activity; Very high = particularly severe levels of influenza activity.
Geographical spread: No activity = no laboratory-confirmed cases, or evidence of increased or unusual respiratory disease activity; Sporadic = isolated cases of laboratory-confirmed influenza infection; Localized = limited to one administrative unit in the country (or reporting site) only; Regional = appearing in multiple but <50% of the administrative units of the country (or reporting sites); Widespread = appearing in >=50% of the administrative units of the country (or reporting sites).
Trend: Increasing = evidence that the level of respiratory disease activity is increasing compared with the previous week; Stable = evidence that the level of respiratory disease activity is unchanged compared with the previous week; Decreasing = evidence that the level of respiratory disease activity is decreasing compared with the previous week.
Dominant type: this assessment is based on data from sentinel and non-sentinel sources.
Sentinel swabs (% pos.): number of sentinels swabs tested for influenza and percentage that tested positive for influenza A or B.
ILI: influenza-like illness.
ARI: acute respiratory infection.
Sentinel SARI: severe acute respiratory illness.
Population: per 100 000 population.
* The value in the table for these countries reflects the percentage (e.g. from 0.0 to 100.0) of total outpatient encounters that were due to ILI/ARI rather than a consultation rate per 100 000 population.
- Not applicable.

Data reported by Member states of the European Union and the European Economic Area are validated by The European Centre for Disease Prevention and Control (ECDC).

The bulletin text was written by an editorial team at the WHO Regional Office for Europe (Diane Gross, Pernille Jorgensen, Dmitriy Pereyaslov, Michala Hegermann-Lindencrone, Caroline Brown and Ganna Bolokhovets as a Temporary Adviser to WHO), the Radboud University Nijmegen Medical Centre, (Tamara Meerhoff, Temporary Adviser to WHO) and the WHO Collaborating Center for Influenza, NIMR, United Kingdom (Rod Daniels). The bulletin was reviewed by Françoise Wuillaume (Scientific Institute of Public Health, Belgium), Rita Born (Swiss Federal Office of Public Health, Switzerland), Natalija Zamjatina (Riga Eastern Clinical University Hospital, Latvia) and ECDC, on behalf of the data contributors.

© World Health Organization 2013. All rights reserved.
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EuroFlu : Weekly Electronic Bulletin