Influenza update - 11 February 2011
Update number 127
Table of contents
- Summary
- Countries in the temperate zone of the northern hemisphere
- Countries in the tropical zone
- Countries in the temperate zone of the southern hemisphere
- Virological surveillance
Summary
Influenza activity is increasing on the European continent, particularly in the central, south and eastern part. In the tropics, several countries of southern Asia have seen a recent increase in influenza virus transmission mainly due to influenza A(H1N1) 2009 virus. Other tropical areas of the world and the temperate countries of the southern hemisphere are currently reporting very little influenza circulation. Influenza transmission in North America, notably in the United States of America (USA) has increased this week with a slight increase of (H1N1) 2009 compared to earlier weeks. Transmission in most of northern Africa and the Middle East has peaked recently and is declining. Some countries in northern Asia are seeing an increase in (H1N1) 2009 transmissions and some are seeing an increase in influenza-like illness activity. The majority of the viruses characterized from North America and Europe are closely related to the vaccine viruses for the current seasonal vaccines.
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Countries in the temperate zone of the northern hemisphere
Europe:
Overall, influenza transmission continues to be high and is increasing in Europe while the countries in the north are starting to show decreasing trends. Of the samples tested from sentinel sites across Europe 46% were positive for influenza virus (43-44% in the previous weeks). The dominant influenza virus in Europe is still (H1N1) 2009. Of influenza viruses detected, 65% were type A and 35% type B (72% A and 28% B in the last update). Of the type A viruses subtyped, 94% were (H1N1) 2009 and 6% influenza A(H3N2). In the western European countries, hospital admissions due to influenza are declining while the eastern countries report an increase. From the western countries, severe cases are in 15- 64 year old age range, a substantial proportion (43%) is not in the known higher risk groups and a majority of them are due to (H1N1) 2009 virus infection. For example, in France, of the cases admitted to intensive care units and for which subtype data are available, 90% were found to have (H1N1) 2009 virus or unsubtyped influenza A, 8% influenza type B and only 1 % influenza A(H3N2), while in the community 43% of the detected viruses are influenza type B and 7% A(H3N2). A similar disparity between mild and severe cases was earlier noted in the United Kingdom.
Characterized viruses in Europe were nearly all antigenically closely related to the current seasonal influenza vaccine viruses, with only a small number of influenza B viruses of the Yamagata lineages detected.
North America: Influenza transmission continued this week across North America, with increasing trends in the USA but declining in Canada. In Canada influenza virus detections in most parts of the country have declined, except in the Atlantic provinces. Other influenza activity indicators are either decreasing or stable compared to earlier weeks. About 18% of specimens tested in Canada are now positive for influenza; influenza type A accounts for 95%, a decrease from previous weeks related to a slight increase of influenza type B detections. Of the influenza type A viruses characterized, 87% are A(H3N2) and the 13% are (H1N1) 2009. In the USA, influenza activity increased. The proportion of outpatient visits for influenza-like illness increased to 4.0% from 2.9% in two weeks, which is above the national baseline of 2.5%. Pneumonia and influenza deaths from 122 cities across the country are currently at 8.5% of total mortality, slightly above the epidemic threshold and increased from two weeks ago (7.5%). About 33% of clinical specimens tested are positive for influenza, an increase from the 26% reported previously. The proportion of the detections accounted for influenza type B was 18%. Of the influenza type A viruses, 63% are influenza A(H3N2) and 37% are (H1N1) 2009. This represents a further increase in the proportion of (H1N1) 2009 in comparison to earlier weeks. In Mexico the percentage of samples positive for influenza was 18%, about half influenza type B and half influenza A(H3N2). Based on the proportion of samples tested positive, influenza activity in Mexico appears to be declining. All of the influenza A viruses from Canada and the USA, and more than 90% of the influenza type B viruses that have been antigenically characterized are closely related to the current seasonal influenza vaccine viruses.
North Africa and the Middle East:
Influenza transmission in North Africa and the Middle East appears to have peaked overall, though Algeria is showing an increase. In Pakistan, Iran and Oman the percentage of samples tested positive for influenza was still rather high (range 28%-70%). (H1N1) 2009 and type B viruses are co-circulating in nearly equal distribution.
Northern Asia: The influenza-like illness activity has been variable in the different countries in northern Asia. A number of countries already went through a peak of influenza activity, and most of these were predominated by A(H3N2), notably northern China and Mongolia, while the Republic of Korea has had a (H1N1) 2009 season which peaked around week 52 of 2010. In recent weeks, however, Mongolia and northern China are reporting an increase in (H1N1) 2009 detections, although without a significant increase in the ILI indicator. Japan is reporting a sharp increase of ILI activity, but does not report as many positive detections of influenza viruses as in previous weeks.
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Countries in the tropical zone
The most active area of transmission in tropical regions of the world continues to be in Asia. In tropical areas of the Americas, reports continue to indicate very little transmission of influenza viruses. In sub-Saharan Africa, available data indicate little activity in most countries. Madagascar, however, shows an increase in influenza activity with a mixture of influenza B and A(H3N2) circulating. In tropical Asia, Singapore and China, Hong Kong Special Administrative Region report respiratory disease activity above their epidemic thresholds with (H1N1) 2009 virus accounting for about 90% of the samples tested. An increase in (H1N1) 2009 positive samples is also reported from southern China. Data from South-East Asia indicate only small numbers of influenza virus detections and no increases in respiratory disease activity.
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Countries in the temperate zone of the southern hemisphere
The countries in the southern temperate regions of the world continue to have very little influenza transmission since the end of their winter season. Australia, however, continues to report out-of-season transmission of influenza A(H3N2) at low level.
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Virological surveillance
During weeks 3 to 4, widespread outbreaks of laboratory confirmed influenza A(H1N1) 2009, A(H3N2) and B viruses continued to be reported in many parts of the northern hemisphere. In general (H1N1) 2009 and B viruses predominated in Asia and Europe. In the North Americas A(H3N2) activity remained high but A(H1N1)2009 activity increased.
FluNet reports
During weeks 3 to 4 (16/01/2011 to 29/01/2011), National Influenza Centres (NICs) from 78 countries, areas or territories reported data to FluNet. A total of 24,543 specimens were reported as positive for influenza viruses, 19,078 (77.7%) were typed as influenza A and 5,464 (22.3%) as influenza B. Of the sub-typed influenza A viruses reported, 77.6% were (H1N1) 2009 and 22.4% were (H3N2).
Influenza virus detection by type/subtype in countries, areas or territories:
- Influenza H1N1 (2009): Albania, Algeria, Australia, Austria, Belarus, Belgium, Bosnia and Herzegovina, Bulgaria, Cameroon, Canada, Chile, China, Costa Rica, Croatia, Cuba, Czech Republic, Denmark, Egypt, Estonia, Finland, France, France - French Guiana, France - Guadeloupe, France - Martinique, Georgia, Germany, Greece, Hungary, Iceland, Iran (Islamic Republic of), Italy, Jamaica, Japan, Kenya, Lao People's Democratic Republic, Latvia, Lithuania, Luxembourg, Madagascar, Mongolia, Morocco, Netherlands, Norway, Oman, Pakistan, Poland, Portugal, Republic of Korea, Romania, Russian Federation, Serbia, Singapore, Slovakia, Slovenia, South Africa, Spain, Sri Lanka, Sweden, Switzerland, Thailand, Tunisia, Turkey, Ukraine, United Kingdom of Great Britain and Northern Ireland and United States of America.
- Influenza A(H3N2): Albania, Australia, Austria, Brazil, Canada, China, Costa Rica, Cuba, Czech Republic, Denmark, France, France - Guadeloupe, France - Martinique, Ghana, Greece, Hungary, Italy, Japan, Madagascar, Mexico, Mongolia, Morocco, Republic of Korea, Russian Federation, Serbia, Singapore, Slovenia, Spain, Sweden, Thailand, Turkey, United Kingdom of Great Britain and Northern Ireland and United States of America.
- Influenza B: Albania, Algeria, Armenia, Australia, Austria, Belarus, Belgium, Brazil, Bulgaria, Cambodia, Cameroon, Canada, China, Costa Rica, Czech Republic, Denmark, Estonia, Finland, France, France - Guadeloupe, France - Martinique, Georgia, Germany, Ghana, Greece, Honduras, Hungary, Iceland, India, Iran (Islamic Republic of), Italy, Japan, Kenya, Kyrgyzstan, Lao People's Democratic Republic, Latvia, Lithuania, Luxembourg, Madagascar, Mexico, Morocco, Netherlands, Norway, Oman, Poland, Portugal, Romania, Russian Federation, Serbia, Singapore, Slovakia, Slovenia, Spain, Sri Lanka, Sweden, Switzerland, Thailand, Tunisia, Turkey, Ukraine, United Kingdom of Great Britain and Northern Ireland and United States of America.
- No influenza activity reported: Afghanistan, Angola, Austria, Azerbaijan, Bangladesh, Central African Republic, Côte d'Ivoire, Dominican Republic, El Salvador, Ethiopia, Mauritius and Senegal.
* Some NICs report to FluNet retrospectively resulting in updates of previous data in FluNet and subsequent charts and maps which based on FluNet data.
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Source of data
The Global Influenza Programme monitors influenza activity worldwide and publishes an update every two weeks.
The updates are based on available epidemiological and virological data sources, including FluNet (reported by the Global Influenza Surveillance Network) and influenza reports from WHO Regional Offices and Member States. Completeness can vary among updates due to availability and quality of data available at the time when the update is developed.
FluNet data as of 8 February 2011, 15:00 UTC.