[Source: EuroFlu, full text: (LINK). Edited.]
EuroFlu - Weekly Electronic Bulletin - Week 47 : 19/11/2012-25/11/2012 - 30 November 2012, Issue N° 464
Generally low influenza activity in Europe, but more countries reporting increasing ILI or ARI rates
Summary, week 47/2012
Levels of influenza activity in the WHO European Region remain low, but more countries are reporting increasing rates of influenza-like illness (ILI) and/or acute respiratory infection (ARI) than in the previous week.
Sporadic detections of influenza A(H1N1)pdm09, A(H3N2) and type B continue to be reported, almost exclusively in the north-western part of the Region.
The number of hospitalizations due to severe acute respiratory infection (SARI) is stable, with very few cases testing positive for influenza to date.
Description of influenza surveillance
The EuroFlu bulletin describes and comments on influenza activity in the 53 countries in the WHO European Region. Most of these countries monitor influenza activity through surveillance of influenza-like illness (ILI) and/or acute respiratory infection (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, which may not use a standard case definition for ILI, ARI or SARI. This report collates and interprets the epidemiological and virological data provided from the different surveillance systems in the Region, to provide information to clinicians, public health specialists and the public on the timing of the influenza season, the spread of influenza in the Region, the prevalence and characteristics of circulating influenza viruses (type, subtype/lineage, antigenic and genetic properties), and severity in terms of numbers of confirmed cases, geographic spread, disease caused and impact on health systems.
Virological surveillance for influenza
This section describes which influenza viruses are circulating according to influenza type (A and B) and subtype (A(H3N2) and A(H1N1)pdm09) or lineage (B/Victoria or B/Yamagata).
Overall, a total of 143 specimens tested positive for influenza in week 47/2012: 77 (54%) were type A and 66 (46%) type B.
Of the influenza A viruses 41 were subtyped: 28 as A(H3N2) and 13 as A(H1N1)pdm09 (Fig. 1).
Since week 40/2012, 637 influenza viruses from sentinel and non-sentinel sources have been typed: 389 (61%) were influenza A and 248 (39%) influenza B.
Of the influenza A viruses 237 were subtyped: 139 (59%) as A(H3N2) and 98 (41%) as A(H1N1)pdm09.
Based on data reported since week 40, influenza virus circulation is largely confined to the north-western part of the Region.
Owing to the low number of viruses detected this week in most countries, only 2 reported on dominant virus type (Norway (influenza B) and Ukraine (influenza A)), as shown in the map below.
Virus strain characterizations
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 susceptibility to antiviral drugs.
In 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 trivalent vaccines (see more at WHO web site).
Since week 40/2012, 2 countries (the United Kingdom (England), Germany) have characterized 13 influenza viruses antigenically (Fig. 3). 6 countries (Finland, Germany, Norway, Portugal, Spain, Sweden) have characterized 24 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.
Monitoring of susceptibility to antiviral drugs
Since week 40/2012, 3 countries (Germany, the Netherlands and Sweden) have screened 15 viruses for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir.
All 9 influenza A(H3N2), 3 A(H1N1)pdm09 viruses and 3 influenza B viruses showed susceptibility to oseltamivir and zanamivir.
The 7 influenza A(H3N2) and 2 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)
In general, consultation rates for ILI and ARI are still at low levels in the Region, with 26 out of 42 countries reporting no influenza activity, and 12 out of 40 reporting increasing trends. The map below presents the weekly intensity, geographic spread and trend for Europe.
The influenza-positivity rate among ILI and ARI cases remains low, with 22 (2.9%) of 758 specimens testing positive for influenza (Fig 2).
Of 758 specimens from sentinel sources, 10 were positive for influenza A (2 A(H1N1)pdm09 and 8 A(H3N2))and 12 for influenza B.
Click here for a detailed overview of cumulative influenza virus detections by type and subtype since week 40/2012.
From non-sentinel samples, 121 specimens were reported positive for influenza: 67 (55%) were influenza A and 54 (45%) were influenza B. Of the influenza A viruses, 31 were subtyped: 20 as A(H3N2) and 11 as A(H1N1)pdm09.
Hospital surveillance for SARI
Similar to week 46, 10 countries (Armenia, Belarus, Georgia, Kazakhstan, Kyrgyzstan, Republic of Moldova, Romania, Russian Federation, Serbia and Ukraine) reported low levels of hospitalizations due to SARI this week. Most of the cases have occurred in the group aged 0–4 years (Fig. 3). Two SARI cases, reported by Kyrgyzstan and the Russian Federation, were positive for influenza B.
In week 47, 122 specimens were collected from hospitalized SARI cases in 8 countries (Belarus, Georgia, Kazakhstan, Kyrgyzstan, Romania, Russian Federation, Serbia and Ukraine). Only 2 tested positive; both were influenza B. Click here for a detailed overview of cumulative influenza virus detections by type and subtype since week 40/2012.
For the countries reporting to the European Centre for Disease Prevention and Control (ECDC) on severe influenza in hospitals, no positive cases were reported this week.
For the surveillance of confirmed hospitalized influenza see the Weekly Influenza Surveillance Overview (WISO) at European Centre for Disease Prevention and Control web site.
'Erratum: The ARI rates for the Republic of Moldova for the past four weeks are not correct. The actual ARI rates remain below the threshold'.
Country comments (where available)
- Denmark: The majority of samples tested positive for influenza A and B in Denmark so far have come from travellers returning from the Middle East.
- Norway: Moderate and increasing number of influenza virus detections. A(H1)pdm09, A(H3) and B Yamagata lineage viruses are circulating sporadically, with influenza B (Yamagata lineage) starting to emerge as the most predominant.
- Republic of Moldova: In the 47th week 15 sentinel samples were tested: 2 specimens were positive for both DNA Adenovirus and RNA hRSV; 1 sample was positive for both DNA Adenovirus and RNA Parainfluenza virus type 2; 5 samples were positive for DNA Adenovirus and 1 sample positive for RNA Parainfluenza virus type 3. Influenza viruses were not detected in any of the tested specimens.
- Spain: From week 40/2012 452 sentinel specimens have been tested for influenza. From them 9 were positive for influenza B virus and 1 for influenza C. No viruses A have been identified so far in Spain. There is a sporadic circulation of B influenza virus (mainly at the North of Spain) and one of them has been genetically characterized as B Yamagata lineage virus (clade B/Wisconsin/1/2010)