Influenza

Influenza update - 17 December 2010

Introduction

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), FluID 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.

Description: Displayed data reflect the most recent information reported to FluNet, WHO regional offices or on ministry of health websites in the last 2 weeks.

The percent of specimens tested positive for influenza includes all specimens tested positive for all influenza subtypes. The pie charts show the distribution of virus subtypes among all specimens that were tested positive for influenza.

The available country data were joined in larger geographical areas (Influenza transmission zones)with similar influenza transmission patterns in order to present an overview.

Influenza - Update 123

17 December 2010 - Summary:

Since the last update, increasing influenza activity has been observed across parts of Europe, most notably in the United Kingdom, indicating the start of wintertime influenza epidemics in several countries. Influenza activity is also increasing in other temperate regions of the Northern Hemisphere, including East Asia and North America where there is evidence of the beginnings of the local winter influenza season. Worldwide, influenza A(H3N2), B, and H1N1 (2009) viruses are co-circulating with significant regional heterogeneity in the predominant circulating influenza viruses.

Countries in the temperate zone of the Northern Hemisphere

In the United Kingdom, the winter influenza epidemic is under way, particularly across England. Since mid to late November 2010 there have reports of increasing numbers of community outbreaks of influenza (due to both influenza H1N1 (2009) and B viruses), increasing proportions of sentinel respiratory specimens testing positive for influenza (56% in England during the second week of December; of which 67% were H1N1 (2009) and 33% were influenza B viruses), and increasing numbers of severe influenza cases requiring intensive care. Available data indicate that the currently circulating strain of the H1N1 (2009) virus in the UK is epidemiologically and virologically similar to that observed last year during the influenza H1N1 2009 pandemic. All influenza viruses characterized to date have been found to be similar to the strains currently included in the seasonal influenza trivalent vaccine. (see below in Virologic Surveillance for details on the characterization of the virus) It is too early to tell what the overall impact of the current epidemic will be in the UK in comparison to the 2009 season.

During the first week of December 2010, small to moderate increases in the levels of ARI or ILI were reported in at least 13 countries across European region, particularly among children <14 years of age. Among 11 countries who have established seasonal baseline levels for ILI or ARI, at least two, the Russian Federation and the Ukraine, reported levels of ILI or ARI above the seasonal baseline. During the last week of November and the first week of December 2010, the proportion of sentinel respiratory specimens testing positive for influenza increased from 5.9% to 9.8%; among the later, 48% and 52% were influenza A and B viruses, respectively. Of the influenza A viruses that were further subtyped, 90% were H1N1 (2009) and 10% were A(H3N2) viruses.

In East Asia, several countries, notably Mongolia and the Republic of Korea, have seen substantial recent increases in influenza activity. In Mongolia, rates of ILI have continued to rise above the seasonal baseline since mid to late November 2010 and were associated with increasing detections of influenza A(H3N2) virus, suggesting that the local winter influenza epidemic is under way. During the same time period in the Republic of Korea, influenza virus detections (of primarily H1N1 (2009) virus) increased substantially, however, overall levels of ILI in the population increased only slightly during the same period. Since mid to late October 2010, levels of ILI in northern (but not southern) China have increased slowly and have been associated with only low levels of circulating influenza A(H3N2) viruses.

Increasing rates of ILI are also noted in North America. In Canada, ILI activity has been geographically variable but overall within seasonal baseline levels, however, during the past two reporting weeks, both the number of influenza virus detections and the proportion of respiratory specimens testing positive for influenza viruses (predominantly A(H3N2) have increase substantially. In the United States, levels of ILI remain at the seasonal threshold in the southwestern region but are otherwise below threshold in other parts of the country; during the past month, influenza B viruses have been detected most frequently, followed by A(H3N2) viruses, and to a much lesser extent, H1N1 (2009) viruses. Persistent, low to moderate, and over time, geographically heterogeneous, circulation of influenza A(H3N2) viruses has been reported in Mexico since early August 2010.

Countries in the tropical zone

In the tropics of the Americas, overall influenza activity remained low. Although influenza A(H3N2) viruses have been predominant across the region during recent months (most notably in Cuba, Paraguay, and in the eastern parts of Bolivia), low levels of H1N1 (2009) virus (in Colombia) and influenza B (in Costa Rica) have also been reported.

In tropics of South and Southeast Asia, overall influenza activity remained low, except in Sri Lanka, where active circulation of H1N1 (2009) along with other influenza viruses, continues to be reported. The current influenza epidemic in Sri Lanka, which began during early October 2010, appears to have recently peaked during the first week of December 2010. To date, there have been no reports from Sri Lanka to suggest an unusual epidemiological or virological pattern of H1N1 (2009) virus infection as compared to last year.

In sub-Saharan Africa, little influenza activity has been reported during the past month, except in Cameroon (central Africa), where there has been a recent surge in the number of detections of H1N1 (2009) viruses. The extent to which the surge in virus detections has been associated with increases in community levels of ILI is not yet known. Elsewhere in sub-Saharan Africa, persistent low to moderate level circulation of influenza A(H3N2) viruses continued to be detected in several countries of East and West Africa, notably in Ghana and Kenya. During early December 2010 in Madagascar, an increase in the proportion of sentinel respiratory samples testing positive for influenza virus was reported. Influenza A(H3N2), H1N1 (2009), and B viruses have co-circulated in Madagascar since early November 2010.

Countries in the temperate zone of the Southern Hemisphere

Overall, only sporadic spring and summertime influenza activity is being reported in countries of the temperate Southern Hemisphere, except in Uruguay, where there is persistent but declining levels of influenza A(H3N2) virus circulation associated with declining indices of severe clinical respiratory diseases in the population.

Virological surveillance

The WHO Global Influenza Surveillance Network is constantly monitoring the evolution of influenza viruses.

Human Infections with swine-origin triple reassortant A(H3N2) viruses.

On December 7, an additional case of human infection with swine-origin triple reassortant A(H3N2) viruses in Minnesota USA were reported through IHR. The Minnesota virus was confirmed by the WHO Collaborating Center in CDC Atlanta. Sequence analysis has shown that the virus is closely related but not identical to the previous swine-origin triple reassortant A(H3N2) viruses from Wisconsin and Pennsylvania in November 2010. To date a total of 6 sporadic cases of human infection of A(H3N2) triple reassortant swine viruses have been reported by CDC since 2005. No known unusual severity has been reported associated with the infection of the A(H3N2) triple reassortant swine virus in humans.

Outbreaks of influenza A H1N1 (2009) and influenza B viruses in the United Kingdom.

A number of severe and fatal cases of influenza A H1N1 (2009) and influenza B have recently been reported by the United Kingdom.

  • Influenza A H1N1 (2009) viruses characterised to date, in samples from the community, hospitalised patients and fatal cases in the United Kingdom, are antigenically homogeneous and similar to the vaccine virus A/California/7/2009.
  • Genetically these H1N1 (2009) viruses have several amino acid substitutions relative to the vaccine virus but these do not affect the antigenicity of the virus and have also been seen in viruses from other parts of the world.
  • The B viruses analysed in the United Kingdom to date are B/Victoria/2/87 lineage viruses and are antigenetically and genetically closely related to the B/Brisbane/60/2008 vaccine virus.

FluNet reports

During weeks 47 to 48 (21 November to 4 December 2010), National Influenza Centres (NICs) from 59 countries reported data to FluNet*. A total of 2,309 specimens were reported as positive for influenza viruses, 1,671 (72.4%) were typed as influenza A, 638 (27.6%) as influenza B. Of the sub-typed influenza A viruses reported, 31.3% were influenza H1N1(2009) and 68.0% were influenza A(H3N2).

Influenza virus detection by type/subtype in countries, areas or territories:

  • Influenza H1N1 (2009): Algeria, Australia, Brazil, Cambodia, Cameroon, China, China Hong Kong SAR, Denmark, Ethiopia, Georgia, Germany, Ghana, Italy, Japan, Kenya, Lao People's Democratic Republic, Lithuania, Luxembourg, Madagascar, Morocco, Netherlands, Norway, Oman, Republic of Korea, Romania, Russian Federation, South Africa, Spain, Sri Lanka, Sweden, Thailand, Togo, United Kingdom and United States of America.
  • Influenza A(H3N2): Algeria, Argentina, Australia, Belgium, Bolivia, Brazil, Cambodia, Cameroon, Canada, Chile, China, China Hong Kong SAR, Cuba, Denmark, France, French Guiana, Ghana, Guadeloupe, Iran (Islamic Republic of), Japan, Kenya, Lao People's Democratic Republic, Madagascar, Mali, Martinique, Mexico, Mongolia, Oman, Paraguay, Republic of Korea, Russian Federation, Slovenia, Spain, South Africa, Sweden, Thailand, Tunisia, United Kingdom and United States of America.
  • Influenza A(H1N1): China, Tunisia.
  • Influenza B: Algeria, Australia, Belgium, Brazil, Cambodia, Cameroon, Canada, Central African Republic, China, China Hong Kong SAR, Costa Rica, Cuba, France, Georgia, Germany, Ghana, Guadeloupe, Honduras, Iran (Islamic Republic of), Italy, Japan, Kenya, Lao People's Democratic Republic, Luxembourg, Madagascar, Mexico, Netherlands, Norway, Oman, Paraguay, Poland, Portugal, Russian Federation, South Africa, Spain, Slovenia, Sri Lanka, Sweden, Switzerland, Thailand, Turkey, United Kingdom and United States of America.
  • No influenza activity reported: Albania, Austria, Azerbaijan, Belarus, Bosnia and Herzegovina, Bulgaria, Croatia, Czech Republic, El Salvador, Estonia, Finland, Greece, Guatemala, Hungary, India, Kazakhstan, Kyrgyzstan, Latvia, Poland, Portugal, Rwanda, Serbia, Ukraine and Zambia.

* Some NICs report to FluNet retrospectively leading to updates of previous summary data.

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