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Date: Thu 31 Jan 2013 Source: World Health Organisation (WHO), Surveillance and Monitoring,

Influenza Update Number 178
- Influenza activity in North America remained high regionally, though
nationally most indicators of transmission began to decrease.
Influenza A(H3N2) was the most commonly detected virus subtype. The
United States of America reported a sharp increase in the number of
pneumonia and influenza-related deaths among adults aged over 65.
- Europe in general reported increasing influenza virus detections
over the past weeks, though activity started to decrease in some
countries in the northwest. The most commonly detected virus across
the continent was A(H1N1)pdm09, while influenza B virus predominated
in several countries of western Europe.
- In the temperate countries of Asia influenza virus detections
increased in the last weeks, while it remained low in most of tropical
- Influenza activity in North Africa and the Middle East declined
overall in the last several weeks, though a few countries reported
increases. Influenza A(H1N1)pdm09 was the most commonly detected virus
in the region.
- Low level activity was noted in most tropical countries, with slight
increases observed in the Plurinational State of Bolivia and Paraguay.

- Influenza in countries of the southern hemisphere were currently at
inter-seasonal levels.

Countries in the temperate zone of the northern hemisphere
North America

Influenza activity in North America during week 3 (13-19 Jan 2013) of
the 2012-13 influenza season remained elevated regionally. While
activity in some areas decreased, both Canada and the U.S. continued
to report widespread transmission of influenza.

Laboratory-confirmed cases of Influenza activity declined for the 3rd
week in a row in Canada nationally, though many regions continued to
report widespread and localized activity. The national influenza-like
illness (ILI) consultation rate decreased from 54.0/1000 patient
visits in the 2nd week of January to 43.8 during the 3rd week of
January, the 4th consecutive week of decline. The percentage of
clinical specimens from ILI patients that tested positive for
influenza also decreased slightly from 30.8 percent to 27.1 percent in
the same period of time; a persistent trend since the end of 2012. For
the past 4 weeks, the national rate of ILI consultation has remained
slightly above the upper 90 percent confidence interval for the 15
year average rate. The number of outbreaks reported in hospitals,
long-term care facilities, and schools peaked at 130 in the 2nd week
of January, more than twice as many as reported in the highest week of
either of the previous 2 influenza seasons. In addition, the 2212
influenza-associated hospitalizations that have been reported through
the Aggregate Surveillance System (a subset of all influenza
admissions in Canada) has surpassed the total of 1777 reported for the
entire previous season. More than half (57.6 percent) of the 2209
cases with available age were aged 65 years ore more and 13.3 percent
were children aged 0-4 years. Since the beginning of the season, 146
deaths have also been reported, 81.5 percent of which were aged 65
years or more. Among 461 influenza-associated pediatric admissions
under the age of 16 years reported through the Immunization Monitoring
Program Active (IMPACT) network since the beginning of the season,
45.1 percent were under the age of 24 months.

Of the 2840 influenza viruses detected in the 3rd week of January,
97.9 percent were identified as influenza A and 2.1 percent were
identified as influenza B. Of the influenza A viruses with subtype
information, 90.6 percent were A(H3N2) and 9.4 percent A(H1N1)pdm09.
The relative proportions of types and subtypes of influenza viruses
has remained consistent throughout the season. Among 461
influenza-associated pediatric hospitalizations reported since the
start of the season 96.3 percent (444/461) have been associated with
influenza A and 3.7 percent (17/461) with influenza B. Most of
influenza A viruses (84.7 percent) were not subtyped; of those with
subtype information, 89.7 percent (61/68) were A(H3N2) and 9.3 percent
(7/68) were A(H1N1)pdm09. The distribution of virus types and subtypes
among hospitalized adults has been similar to that in paediatric

Since the start of the season, the National Microbiology Laboratory
has antigenically characterized 285 influenza viruses (201 A(H3N2), 37
A(H1N1)pdm09, and 47 influenza B). Of these, all influenza A(H3N2) and
A(H1N1)pdm09 viruses were antigenically similar to the vaccine strains
A/Victoria/361/2011 and A/California/07/09 respectively. Among the
influenza B viruses, 37 were antigenically similar to the vaccine
strain B/Wisconsin/01/2010 (Yamagata lineage) and 10 were similar to
B/Brisbane/60/2008 (Victoria lineage; component of the 2011-2012
seasonal influenza vaccine). Thus far in the 2012-13 season, 274
influenza viruses have been tested for sensitivity to the
neuraminidase-inhibitors, oseltamivir and zanamivir, none were

Influenza activity in the United States of America (USA) remained high
during the 3rd week of January, but decreased in some areas;
nationally activity appears to have peaked in the last 2 weeks of
December. Nationally, the proportion of outpatient consultations that
were due to ILI decreased for the 4th consecutive week to 4.3 percent
from a peak of 6.1 percent in the last week of 2012. The proportion of
clinical ILI specimens testing positive for influenza also declined in
the same period from 37.6 percent at the end of 2012 to 26.1 percent
in the 3rd week of January. As in the last report, 47 states reported
widespread geographic influenza activity. The proportion of all deaths
attributed to pneumonia and influenza (P&I) reported through the 122
Cities Mortality Reporting System increased sharply to 9.8 percent in
the 3rd week of January, well above the epidemic threshold of 7.3
percent. In the previous 10 years period, the highest reported peak of
P&I mortality was 9.1 percent in the 2007-8 influenza season.

In that year, the P&I mortality exceeded the epidemic threshold for 8
consecutive weeks. In contrast, 34 influenza-related paediatric deaths
have been reported so far this season, compared to sonsons37 for the
entire season in 2011-12, 122 in 2010-11, and 282 during the winter
season of 2009-10 influenza pandemic. A total of 6191
laboratory-confirmed influenza related hospitalizations have been
reported since the beginning of the season (cumulative rate of
22.2/100 000 population). While this has not yet peaked, it is higher
than the previous 2 seasons (8.6 and 21.4/100 000 population for the
2011-12 and 2010-11 seasons respectively) but not as high as the
2009-10 season (29.0/100 000). However, the rate for individuals over
age 65 years has reached 97.7/100 000 compared to year-end cumulative
totals of 25.3, 64.0, and 30.5/100 000 for the years 2009-10, 2010-11,
and 2011-12 respectively.

In contrast to Canada, in the USA a higher proportion of detected
influenza viruses are influenza B. Of 40 962 influenza viruses
reported since the beginning of the season, 80.1 percent were
influenza A and 19.9percent, influenza B. However, as in Canada, 98
percent of the influenza A viruses with subtype information were
A(H3N2). Since the beginning of the 2012-13 influenza season, the
Centers for Disease Control and Prevention (CDC) has antigenically
characterized 751 influenza viruses. All 54 A(H1N1)pdm09 viruses
tested were characterized as A/California/7/2009-like and 99.6 percent
(463/465) of the A(H3N2) influenza viruses tested were
A/Victoria/361/2011-like, both of which are components of the 2012-13
Northern Hemisphere trivalent influenza vaccine. Of the 232 influenza
B viruses tested, 69 percent (160/232) were characterized as
B/Wisconsin/1/2010-like of the Yamagata lineage, a component of this
season's trivalent influenza vaccine, and 31 percent (72/232) were of
the Victoria lineage.

None of the 762 influenza A(H3N2) and 274 influenza B viruses tested
for sensitivity to the neuraminidase-inhibitors oseltamivir and
zanamivir since the beginning of the season have been resistant. The
first oseltamivir-resistant A(H1N1)pdm09 virus has been reported
during the 3rd week in January out of 119 tested.

Influenza activity in Europe in the 3rd week of January increased in
majority of countries of the region compared to the previous report,
though some decreases have also been reported, particularly in the
northwest. Increasing activity was reported in 17 countries, compared
to 19 countries in the previous report, while decreasing trends were
reported in 5 countries including Denmark, Ireland, the Netherlands,
Norway, and the United Kingdom, compared to only 2 countries in the
previous report. The proportion of ILI and Acute Respiratory Infection
specimens testing positive for influenza was nearly the same for 3
consecutive weeks across the continent at about 40 percent but in the
western part of the continent has declined slightly from a peak at the
end of December 2012. Among individual countries, numbers of reported
ILI cases are similar in magnitude to recent previous seasons. In
England, the number of registered respiratory deaths and all cause
deaths have been similar to previous influenza seasons. Pooled numbers
of all-cause deaths reported by 13 countries participating in the
European Mortality Monitoring project have also been close to
historical median values.

The most commonly detected viral subtype in the region was influenza
A(H1N1)pdm09 but the distribution varied among individual countries
and has changed since the beginning of the season. Since the start of
the 2012-13 season, 69 percent of 16 457 influenza viruses reported
from sentinel and non-sentinel sources have been type A and 31 percent
B across the continent. However, influenza B was more common in a few
countries of western Europe including Ireland, Italy, and the United
Kingdom, while more eastern countries including the Czech Republic,
Germany, Poland, and the Russian Federation reported much more
influenza A. Influenza A(H1N1)pdm09 has increased in proportion over
the course of the season and now accounts for 80 percent of influenza
A viruses with subtype information in the 3rd week of January.
However, overall for the season, influenza A(H1N1)pdm09 accounted for
only 68 percent of influenza viruses and A(H3N2) 32percent. Notably,
in the UK, while influenza B was the most commonly detected virus in
outpatient clinics, influenza A(H1N1)pdm09 and A(H3N2) was found in a
much larger proportion of hospitalized cases in all age groups. In
data from European sentinel sites the proportions of viruses found in
ILI and ARI specimens is similar to that found in hospitalized cases.

Since the start of the 2012-13 season, the majority of viruses
characterized are antigenically similar to the viruses included in the
current Northern Hemisphere seasonal influenza vaccine.

Since the start of the 2012-13 season, 7 countries have screened 196
viruses for susceptibility to neuraminidase inhibitors (oseltamivir
and zanamivir) and found all to be sensitive.

Northern Africa and the eastern Mediterranean region
Across the North Africa and the Middle East region, the number of
positive specimens reported has been decreasing over the past 5 weeks,
although increases were reported in individual countries. Of the
countries currently reporting, Algeria, Israel, the Islamic Republic
of Iran and Pakistan have noted increases in influenza activity. In
the Northern Africa region, Tunisia also reported transmission
increases. The Islamic Republic of Iran and Qatar noted decreases in
influenza activity. The most commonly reported virus also varied
between countries. Pakistan and Qatar reported more influenza B, while
Algeria, The Islamic Republic of Iran, and Iraq reported more
influenza A(H1N1)pdm09. Israel reported a nearly equal numbers of
influenza A(H3N2) and A(H1N1)pdm09.

Temperate Asia
Influenza activity continued to increase throughout most of the
temperate region of Asia during the 3rd week of January, including
northern China, Mongolia and the Republic of Korea. The proportion of
outpatient visits at sentinel surveillance sites that were due to ILI
in northern China was 5.1 percent, which was similar to that of the
previous report (4.2 percent). The proportion of influenza
A(H1N1)pdm09 has continued to increase in the area, approaching equal
proportions with influenza A(H3N2). Influenza A accounted for 99.2
percent (387/390) of influenza viruses detected. Of the influenza A
that were sub-typed, 54.3 percent were A(H3N2) and 45.6 percent were

Among influenza viruses antigenically characterized by the Chinese
National Influenza Center since October, 2012, 99 percent (n=101)
influenza A(H1N1)pdm09 viruses are related to
A/California/7/2009-like, 100 percent (n=397) of influenza A(H3N2)
viruses are related to A/Victoria/361/2011(H3N2)-like; 96 percent
(n=121) of influenza B/Victoria viruses are related to
B/Brisbane/60/2008-like; and 100 percent (n=19) influenza B/Yamagata
viruses are related to B/Wisconsin/01/2010-like. None of the influenza
samples tested were resistant to the neuraminidase inhibitors,
oseltamivir and zanamivir. In Mongolia, ILI activity based on the
proportion of outpatients has increased slightly. Much of ILI in
recent weeks has been associated with other respiratory viruses, such
as respiratory syncytial virus, rhinovirus and human coronaviruses.

Influenza activity continued to increase in the Republic of Korea,
with detections of A(H3N2) and A(H1N1)pdm09. Influenza activity
remained low in Japan, with influenza A(H3N2) the dominant sub-type

Countries in the tropical zone
Tropical countries of the Americas
In both Central America and the Caribbean, influenza activity in the
3rd week of January was similar or declined compared to previous weeks
and continued to decrease from their peaks in late summer. The most
commonly detected viruses were influenza A(H3N2) and B, with Cuba
being the only exception and where influenza A(H1N1)pdm09 was
observed. In French Territories, Martinique and Guadeloupe are
experiencing higher number of ILI consultations than the expected
levels for previous years but no influenza virus was reported.

Throughout South America, influenza activity was at undetectable or
low level with the exception of slight increases in activity seen in
Paraguay and the Plurinational State of Bolivia. Paraguay reported
circulation of both influenza A(H3N2) and B, while the Plurinational
State of Bolivia, reported a moderate increase in circulation of
A(H3N2) alone.

Central African Belt
Most countries in the Central African Belt experienced decreasing
detections of influenza. Influenza A(H1N1)pdm09 that had been
circulating previously in the Democratic Republic of the Congo and
Ghana has decreased to inter-seasonal levels. Cameroon and Madagascar
continued to report low levels of influenza B.

Tropical Asia
Influenza activity in most countries of south East Asia has remained
similar to previous weeks, with continuing low-level circulation in
Cambodia, Sri Lanka, Thailand and Viet Nam.

Influenza activity in India remained at inter-seasonal levels, with
low detections of mainly influenza A(H1N1)pdm09 and some influenza B.
Sri Lanka reported consistent circulation of all three influenza
sub-types, while influenza A(H3N2) and influenza B were detected in
Thailand. Cambodia and Viet Nam reported transmission of predominantly
influenza B virus.

Influenza activity in Singapore and southern China, including Hong
Kong SAR, remained below seasonal thresholds. In southern China, the
proportion of influenza A(H1N1)pdm09 has increased and exceeded the
proportion of influenza A(H3N2). Influenza A accounted for 97.5
percent (157/161) of influenza viruses detected. Of the influenza A
that were sub-typed, 47.2 percent were A(H3N2) and 52.7 percent were
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