15 Mar 2013

Weekly Electronic Bulletin - Week 10 : 04/03/2013-10/03/2013 - 15 March 2013, Issue No. 479 (edited)

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

Weekly Electronic Bulletin - Week 10 : 04/03/2013-10/03/2013 - 15 March 2013, Issue No. 479

Continued decline in consultation rates in most European countries with medium activity and widespread circulation of influenza

 

Summary, week 10/2013

  • During week 10/2013, consultation rates for influenza-like illness (ILI) and/or acute respiratory infection (ARI) continued to decline in most parts of the WHO European Region.
  • Most countries reported medium activity, widespread circulation of influenza and a high percentage of sentinel specimens testing positive for influenza.
  • The proportion of type B viruses detected in sentinel sources increased, mainly in countries in southern and central parts of the Region.
  • A(H1N1)pdm09 remained dominant in outpatient surveillance and patients hospitalized for severe acute respiratory infection (SARI), but the number of SARI cases started decreasing, along with the number of hospitalized cases testing positive for influenza.

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 10/2013, a total of 5980 specimens tested positive for influenza, with 3638 (61%) positive for influenza A (Fig. 1). The proportion of influenza A viruses has gradually decreased since week 3/2013, when 76% of specimens tested positive.

Influenza A(H1N1)pdm09 remained the dominant A virus with similar proportions observed for several weeks: of 2185 subtyped, 1459 (67%) were A(H1N1)pdm09 and 726 (33%) were A(H3N2) (Fig. 2a).

Since the beginning of the season (week 40/2012), 72 137 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, 47 619 (66%) were influenza A and 24 518 (34%) influenza B (Fig. 2b).

Of the 30 589 influenza A viruses that have been subtyped, 21 688 (71%) were A(H1N1)pdm09 and 8901 (29%) were A(H3N2).

The lineage for 3669 influenza B viruses was determined, with a similar distribution of influenza B viruses to the previous week: 3350 (91%) belonged to the B/Yamagata lineage and 319 (9%) to B/Victoria.

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The circulation of influenza viruses still varied across the Region in week 10/2013.

Influenza A, mainly A(H1N1)pdm09, was reported as the dominant virus by countries in eastern and central Europe, Ireland and the United Kingdom (England and Northern Ireland), while influenza B was reported as dominant in some countries in the southern and central parts of the Region, Denmark and Norway. Between these areas, more countries reported co-circulation of influenza A (mainly A(H1N1)pdm09) and B (Map 1) in week 10/2013 than the previous week.

 

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 recommendations for the 2013/2014 northern hemisphere influenza season (see the WHO headquarters web site).

Since week 40/2012, 3426 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, Scotland)) corresponded with the viruses recommended by WHO for inclusion in the current northern hemisphere seasonal influenza vaccine (Fig. 3).

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 1070 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.

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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

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 787 viruses for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir.

Of the 324 A(H1N1)pdm09 viruses tested, 316 showed susceptibility to both drugs, and 8 viruses carried the neuraminidase H275Y amino acid substitution, causing resistance to oseltamivir. 1 virus from the Russian Federation was detected in a hospitalized patient and 2 viruses from the United Kingdom were detected in outpatients not exposed to oseltamivir through treatment. 5 viruses from Germany (2) the Netherlands (2) and Switzerland (1) were detected in hospitalized immunocompromised patients exposed to oseltamivir through treatment.

The 207 influenza A(H3N2) tested showed susceptibility to both drugs.

Of the 256 influenza B viruses tested, 255 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)

In comparison with week 9/2013, many more countries all over the Region reported decreasing influenza activity in week 10/2013 (Map 4). Nevertheless, most countries continued to report medium intensity levels (Map 2) and widespread circulation of influenza (Map 3).

Of the countries that have established epidemic thresholds, the Czech Republic, France, Israel, Kyrgyzstan and Ukraine reported ILI/ARI consultation rates below their national threshold levels.

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The percentage of sentinel specimens testing positive for influenza remained high: in week 10/2013, 1887 sentinel specimens were tested, of which 945 (50%) were positive for influenza, similar to week 9/2013 (Fig. 5).

In the 23 countries testing 20 or more sentinel specimens, influenza positivity ranged from 5% to 77%, with a median of 54% (mean: 50%).

Of the 945 influenza-positive specimens from sentinel sources, 55% were positive for influenza B. The proportion of sentinel samples testing positive for influenza B, has gradually increased since week 3/2013 (Fig. 6a). Similarly to the two previous weeks, most of the influenza B detections were reported by France, 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.

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Hospital surveillance for SARI

In week 10/2013 the number of SARI hospitalizations and the proportion of SARI respiratory specimens testing positive for influenza decreased from the levels seen in previous weeks (Fig. 7). This is concurrent with decreasing influenza activity in most of the countries taking part in hospital surveillance for SARI.

The decreasing trend in the number of SARI hospitalizations indicates that they have peaked for the season in Albania, Belgium, Kyrgyzstan and the Russian Federation.

During week 10/2013 Georgia and Ukraine showed increased cases in the groups aged 30–64 and/or ≥65 years, coinciding with increased positivity rates.

For week 10/2013, similarly to the two previous weeks, 12 countries (Armenia, Belarus, Belgium, Georgia, Kazakhstan, Kyrgyzstan, the Republic of Moldova, Romania, the Russian Federation, Serbia, Slovakia and Ukraine) reported 97 influenza detections among 365 specimens tested, 77% of which were influenza A (Fig. 8a). Most of the detections were reported by 5 countries (Armenia, Georgia, Romania, the Russian Federation and Ukraine). Since week 40/2012, 5189 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), 78 such cases were reported for week 10/2013. 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 graphsfor 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 10/2013 data, based on 15 countries or regions, showed excess mortality among people aged 65 and older since week 01/2013.

No excess mortality in younger age groups has been detected so far this season.

Results of pooled analysis may vary dependent on which countries are included in the weekly analysis. 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)

  • Republic of Moldova: During week 10/2013, 1 death from seasonal influenza A (H1N1)pdm09 (non-sentinel) were registered: 1 male aged 62 in Cantemir district. Patient asked late for medical care, and antiviral treatment was initiated late. Neither had been vaccinated against influenza.  In addition, 37 samples were tested for Influenza viruses, of which 8 were positive for RNA influenza virus A(H1N1)pdm09; 4 samples, positive for RNA influenza virus A(H3N2); and 4, for RNA influenza virus type B.
  • Romania: one of the laboratory confirmed cases was a double infection (coinfection): SWOAH1 and B virus

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