EuroFlu - Weekly Electronic Bulletin - Week 45 : 05/11/2012-11/11/2012 - 16 November 2012, Issue N° 462: 63% of A typed viruses were H1pdm09

[Giuseppe Michieli]

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


EuroFlu - Weekly Electronic Bulletin - Week 45 : 05/11/2012-11/11/2012 - 16 November 2012, Issue N° 462

Influenza detections in Europe still sporadic



Summary, week 45/2012

Influenza activity in the WHO European Region remains at a pre-season level, with several countries reporting sporadic detections of influenza A(H1N1)pdm09, A(H3N2) and type-B viruses.

The influenza positivity rate is relatively stable, as is usual for this time of the year.

The number of hospitalizations due to severe acute respiratory infection (SARI) remains stable, with none of the cases reported this week due to influenza.



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 and 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 and lineage), and severity.



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 of B/Yamagata). Where there are sufficient data, the dominant virus type and/or subtype/lineage is shown for individual countries. 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 susceptibility to antiviral drugs.



Circulation of influenza viruses

Overall, a total of 95 specimens tested positive for influenza in week 45/2012, slightly more than in week 44/2012: 56 were type A and 39 were type B.

Of the influenza A viruses, 33 were subtyped: 12 as A(H3) and 21 as A(H1)pdm09 (Fig. 1).

Since week 40/2012, 311 influenza viruses from sentinel and non-sentinel sources have been typed: 206 (66%) were influenza A and 105 (34%) influenza B.

Of the influenza A viruses 121 were subtyped: 64 (53%) as A(H3) and 57 (47%) as A(H1)pdm09.

Owing to the low number of viruses detected in week 45/2012 only 1 country (United Kingdom (Scotland)) reported a dominant virus, as influenza A and B, as shown in the map below.



Virus strain characterizations

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, 1 country (Germany) has characterized 3 influenza viruses antigenically:

• 2 were A(H3N2) viruses (A/Victoria/361/2011 (H3N2)-like) and
• 1 influenza B virus was B/Wisconsin/1/2010-like (B/Yamagata/16/88 lineage).

This corresponds with the viruses recommended by WHO for inclusion in the current northern hemisphere seasonal influenza vaccine.

2 countries (Norway and Sweden) have characterized 4 influenza viruses genetically, 1 A(H3N2), 1 A(H1N1)pdm09 and 2 influenza B viruses (Yamagata lineage).

• 1 A(H3N2) virus belonged to the subgroup (3C) represented by A/Victoria/361/2011 in the A/Victoria/208/2009, A(H3) clade);
• 1 A(H1N1)pdm09 belonged to the group (6) represented by A/St Petersburg/27/2011 in the A(H1N1)pdm09 clade;
• 1 influenza B virus belonged to the clade 3 represented by B/Wisconsin/1/2010 in the B(Yamagata) lineage and
• 1 belonged to the clade 2 represented by B/Estonia/55669/2011 in the B(Yamagata) lineage.

Monitoring of susceptibility to antiviral drugs

Since week 40/2012, 2 countries (the Netherlands and Sweden) have screened 4 viruses for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir. All 3 A(H3N2) viruses and the single A(H1N1)pdm09 virus showed susceptibility to oseltamivir and zanamivir. The 3 influenza A(H3N2) viruses were screened for susceptibility to adamantanes and found to be resistant.



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

Consultation rates for ILI and ARI continue to be low, as usual for this time of the year, throughout the WHO European Region.

Only 13 of 41 countries reported sporadic geographic spread, while 7 of 40 reported increasing trends.

Similar to the previous week, only 1 among 18 countries that have established epidemic thresholds (the Republic of Moldova) reported ILI/ARI consultation rates for above their national threshold. The map below presents the weekly intensity, geographic spread and trend for Europe.

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The influenza-positivity rate among ILI and ARI cases from sentinel sources increased slightly, along with the number of specimens tested: 14 (2.3%) of 608 specimens tested were influenza positive. The number of specimens testing positive for influenza in weeks 40–45/2012 remains below the set cut-off for presentation, which requires at least 20 positive specimens per week (see Fig. 2).

Of 608 specimens from sentinel sources, 14 tested positive for influenza A. This week 4 influenza B viruses were detected, in comparison with none last week. Click here for a detailed overview of cumulative influenza virus detections by type and subtype since week 40/2012.
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81 specimens were reported positive for influenza: 46 were influenza A and 35 were influenza B. Of the influenza A viruses, 28 were subtyped: 7 as A(H3N2) and 21 as A(H1)pdm09.

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Hospital surveillance for SARI

Sentinel SARI hospitalization rates are still low and at pre-season levels, with most of the cases occurring in the group aged 0–4 (Fig. 3). Similar to week 44, 9 out of 11 reporting countries (Armenia, Belarus, Georgia, Kazakhstan, Kyrgyzstan, Republic of Moldova, Russian Federation, Serbia and Ukraine) reported hospitalizations due to SARI. None of these SARI cases was positive for influenza.

A total of 106 specimens was collected from hospitalized SARI cases in 8 countries (Armenia, Belarus, Georgia, Kazakhstan, Kyrgyzstan, Russian Federation, Serbia and Ukraine).Click here for a detailed overview of cumulative influenza virus detections by type and subtype since week 40/2012.

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For the surveillance of confirmed hospitalized influenza see the Weekly Influenza Surveillance Overview (WISO) at European Centre for Disease Prevention and Control web site.

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Country comments (where available)

Belgium: Four adult persons recently coming back from the Hajj in Saudi Arabia presented respiratory symptoms and were tested for respiratory viruses. Two tested positive for influenza B, one tested positive for influenza A and one was negative. Among the 4 persons was a couple with discordant results, the women testing positive for influenza A and the man testing positive for influenza B. The other persons had no epidemiologic links. No other respiratory viruses, including coronavirus, have been identified.

Greece: During the weeks 42-44, nineteen specimens from paediatric patients with ARI in Southern Greece found negative for influenza virus, were tested for other respiratory viruses. Human rhinoviruses (n=2), human enteroviruses (n=2) and human respiratory syncytial virus type B (n=1) were detected in these specimens by molecular methods.

Norway: Low but increasing number of influenza virus detections. A(H1)pdm09, A(H3) and B Yamagata lineage viruses appear to be circulating sporadically, in approximately equal numbers.

Republic of Moldova: This week from 16 sentinel specimens, 2 samples were positive for RNA Parainfluenza type I and type III, respectively.

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