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Archive Number 20110107.0086
Published Date 07-JAN-2011
Subject PRO/EDR> Influenza (02): UK
INFLUENZA (02): UNITED KINGDOM
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A ProMED-mail post
<http://www.promedmail.org>
ProMED-mail is a program of the
International Society for Infectious Diseases
<http://www.isid.org>
Date: Thu 6 Jan 2011
Source: Eurosurveillance, Volume 16, Issue 1 [abbreviated and edited]
<http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19760>
Ref: Virological analysis of fatal influenza
cases in the United Kingdom during the early wave
of influenza in winter 2010/11.
By J Ellis and 11 others
Health Protection Agency, Centre for Infections, London, United Kingdom
Summary
-------
The 2010/11 winter influenza season is underway
in the United Kingdom, with co-circulation of
influenza A(H1N1)2009 (antigenically similar to
the current 2010/11 vaccine strain), influenza B
(mainly B/Victoria/ 2/87 lineage, similar to the
2010/11 vaccine strain) and a few sporadic
influenza A(H3N2) viruses. Clinical influenza
activity has been increasing. Severe illness,
resulting in hospitalisation and deaths, has
occurred in children and young adults and has
predominantly been associated with influenza
A(H1N1)2009, but also influenza B viruses.
Introduction
------------
The onset of this winter season in the northern
hemisphere is associated with more uncertainty
than usual about which influenza viruses are
likely to circulate and predominate, given the
varying proportions of different virus strains
circulating in the southern hemisphere between
June and September 2010 [1]. Notably, influenza
A(H3N2) predominated over influenza A(H1N1)2009
in several countries, e.g. South Africa and
Chile. The 2nd wave of the pandemic in the United
Kingdom (UK) during the winter season of 2009/10
was almost exclusively associated with
circulation of influenza A(H1N1)2009 [2].
Serological evaluation in the UK of population
immunity to the pandemic strain after the 2nd
wave suggested that susceptibility was lowest in
younger age groups (<15 years), with significant
remaining susceptibility in the age group of 1544 year-olds [3].
In view of the importance of children in the
transmission of influenza A(H1N1)2009 [4], and
the limited remaining susceptibility within this
group, the probability of extensive morbidity in
this age group associated with this strain in
winter 2010/11 was considered unlikely in the
absence of significant antigenic change in the
pandemic virus. The extent, however, to which
influenza A(H1N1)2009 would predominate over
influenza A(H3N2) and cause illness in the
remaining susceptible children and younger adults was unknown.
Investigations
--------------
Virological surveillance in the UK operates
through hospital laboratories in secondary care
and community-based schemes. Specimens containing
influenza virus from community, hospitalised and
fatal cases are forwarded to the UK National
Influenza Centre for further characterisation.
Samples are also received directly from sentinel
primary care physicians participating in
virological surveillance schemes in the community
[5]. An antigenic typing profile is developed for
each virus isolate and compared with influenza
vaccine and reference strains. Genotypic and,
where appropriate, phenotypic antiviral
susceptibility analyses are performed on
influenza-positive clinical material and/or virus
isolates. Genetic characterisation is performed
by targeted haemagglutinin (HA) sequence analysis
and/or whole genome sequencing for a subset of
isolates (primer sequences available on request).
[Epidemiological findings -- the data, figures,
tables, references and accompanying text -- are
omitted and interested readers are referred to
the original article for this information. Only
the discussion and conclusions are presented here
on account of their general interest.]
Discussion and conclusions
--------------------------
Early detections of influenza A(H1N1)2009 virus
were 1st reported in weeks 4042 from cases in
the community. Indicators of clinical activity
began to rise in week 47 crossing the traditional
baseline threshold level indicating generalised
influenza activity in the community in week 49,
and have continued to increase up to week 52.
Influenza virus circulation is underway in the UK
and is contributing to seasonal winter pressures
in the health system. The circulation of other
winter viruses such as respiratory syncytial
virus (RSV) and the particularly cold weather are
also contributing. The virological picture is
complex, with many strains of influenza virus
circulating but no antigenic change in the
influenza A(H1N1)2009 virus, and no immediately
obvious genetic differences between viruses
recovered from fatal cases and those causing mild illness.
The picture of the illness associated with
influenza A(H1N1)2009 infection is consistent
with what was seen in the 2009 pandemic, with a
similar demographic impact, particularly
affecting children and young adults. Whilst young
age groups have the least experience of influenza
and are recognised as important in the
transmission of influenza, it is also possible
that propensity to consult a doctor is greatest
in younger age groups. Although the remaining
susceptibles in the age group under 15 year
account for high rates of positivity in peak
weeks in community samples (as is often the case
during seasonal influenza), it is notable that
overall, sustained high rates of positivity are
most marked in the age group between 15 and 44
years. This is in contrast to earlier pandemic
waves in 2009 when highest rates of positivity in
the community were observed in the 5-14 year-olds.
The age group of 15-44 year-olds is also clearly
the major group contributing to hospital
admissions and deaths. The increase in
requirement for critical care in the current
season reflects the impact of influenza
A(H1N1)2009 illness in the remaining susceptible
young adults (15-44 years) and risk groups in the population.
Most of those with severe illness, and those
dying, have not previously been vaccinated
against influenza and have not had the benefit of
the early use of antiviral drugs. Countries in
Europe yet to experience substantial influenza
activity this winter may wish to take all
reasonable measures to increase the uptake of
seasonal influenza vaccine in those at high risk
of the complications of influenza and to ensure
that antiviral drugs are readily available for
those who are either severely ill or at increased
risk of severe illness from influenza.
---
Communicated by:
ProMED-mail
<promed@promedmail.org>
[The important interim conclusions of this
analysis are that the virological picture is
complex, with many strains of influenza virus
circulating but no antigenic change in the
influenza A(H1N1)2009 virus, and no immediately
obvious genetic differences between viruses
recovered from fatal cases and those causing mild
illness. The picture of the illness associated
with influenza A(H1N1)2009 infection is
consistent with what was seen in the 2009 pandemic.
To put this information in perspective the
corresponding situation throughout Europe
according to the EuroFlu - Weekly Electronic
Bullet of Fri 7 Jan 2010
(<http://www.euroflu.org/cgi-files/bulletin_v2.cgi>)
is the following: "Increasing consultation rates
were reported by 12 of the 32 countries
submitting data on influenza-like illness (ILI)
and/or acute respiratory infection (ARI), mostly
in children aged 0-4 years. In the United Kingdom
(England), the group aged 5-14 was most affected.
Of the 10 countries presenting calculated
baseline thresholds, 5 (France, Ireland, Israel,
Luxembourg and Ukraine) reported clinical
consultation rates above the thresholds. Denmark
and the United Kingdom (England) reported a high
intensity of influenza activity.
"Of the 38 countries reporting on the
geographical spread of influenza, 11 reported
widespread activity; 5 reported regional
activity; 6 reported local activity and the
remaining 16 reported no or sporadic activity.
The impact of influenza on health care systems
was low in 16 of the 21 countries reporting on
this indicator, with Ireland, Israel, the United
Kingdom (Wales and Scotland) and Turkey reporting moderate impact."
The HealthMap/ProMED-mail interactive map of the
United Kingdom can be accessed at: <http://healthmap.org/r/008E>. - Mod.CP]
[see also:
Influenza: Egypt 20110103.0029
2010
----
Influenza (26): Russia (SV) H1N1 20101231.4612
Influenza (25): Europe 20101231.460
Influenza (24): Sri Lanka 20101224.4532
Influenza (23): USA, Egypt, Sri Lanka 20101223.4519
Influenza (22): WHO update 123 20101221.4495
Influenza (21): Egypt (NS) H1N1 fatal 20101218.4467
Influenza (20): WHO, Europe, UK 20101217.4463
Influenza (19): Europe, Israel, Yemen 20101216.4454
Influenza (18): WHO update, UK 20101212.4418
Influenza (17): Canada (MB), 1st nation 20101203.4341
Influenza (16): Zimbabwe (MV) 20101126.4274
Influenza (15): WHO update 20101124.4243
Influenza (14): swine origin (tr) H3N2 viruses 20101112.4117
Influenza (13): WHO update 20101111.4092
Influenza (06): WHO update 116 20100912.3295]
...................cp/ejp/mpp