Influenza

Influenza update - 8 November 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 120

8 November 2010 - Summary:

Worldwide, overall influenza activity remained low, except in parts of the tropics, most notably in Southeast Asia, and to a lesser extent in the tropical areas of the Americas. After late winter and springtime influenza epidemics in several countries of the temperate southern hemisphere, influenza activity has returned to near or below baseline in most places. Notably, however, a recent post-season rise in cases has been noted across parts of southern Africa associated with localized outbreaks of influenza H1N1 (2009) virus. Seasonal influenza A(H3N2) viruses continued to be the predominant circulating type or subtype of influenza viruses worldwide, however, in addition, in many countries there has been co-circulation of seasonal influenza B viruses and to a lesser extent, influenza H1N1 (2009) viruses. The latter has been recently predominant in a limited number of countries, including in India.

Countries in the temperate zone of the Southern Hemisphere

In Chile, an unusually late winter and springtime influenza epidemic, characterized by predominance of circulating seasonal influenza A (H3N2) viruses, and to a lesser extent seasonal influenza B and H1N1 (2009) viruses, appears to have largely subsided. A similarly timed influenza epidemic was also observed in Paraguay and Uruguay. In Argentina, however, little winter and springtime influenza activity was observed during 2010, with influenza B viruses accounting for the majority of sporadic influenza virus detections.

In South Africa, the 2010 winter influenza season, characterized by a predominance of seasonal influenza B viruses, and to lesser seasonal A(H3N2) viruses, had largely concluded by the end of September 2010 but was followed by a mild resurgence of influenza activity (with a similar distribution of influenza viruses) during October 2010. In neighboring Namibia, there have been reports of school and community outbreaks of influenza H1N1 (2009) during October 2010.

As of early to mid-October 2010, influenza activity had declined substantially or had fallen below seasonal baselines in Australia and New Zealand, respectively. In both countries, the season was marked by a predominance of circulating influenza H1N1 (2009) viruses, however, in Australia there was also co-circulation of seasonal A (H3N2) and B viruses.

Countries in the tropical zone

In the tropics of Asia, the most active reported circulation of influenza viruses continued to be in Thailand. Since late July 2010, influenza H1N1 (2009) viruses have been the predominant circulating influenza viruses in Thailand, however, more recently beginning in early October 2010, seasonal influenza A(H3N2), B, and H1N1 (2009) viruses began to co-circulate at similar levels. In southern China and Hong Kong (SAR), recent periods of active circulation of seasonal influenza A(H3N2) viruses during late summer and autumn now appear to have largely subsided. In Hong Kong SAR (China) but not in southern China, circulation of seasonal influenza A(H3N2) viruses was associated with a significant increase in sentinel levels of ILI activity. In India, the national epidemic of influenza H1N1 (2009), which began during June 2010 and lasted until late September 2010, has largely subsided but small numbers of new cases continued to reported weekly. In neighboring Bangladesh, there has been persistent influenza virus transmission since the early part of 2010, however, only in recent months has circulation of seasonal influenza A(H3N2) become predominant.

In the tropics of the Americas, between late July and early October, many countries or parts of countries experienced periods of active circulation of influenza viruses, including but not limited to southern Mexico, Costa Rica, Nicaragua, El Salvador, Honduras, Jamaica, Cuba, Peru, Colombia, and Bolivia. In most of these countries, seasonal influenza A(H3N2) was the predominant circulating influenza virus. Notably, Nicaragua observed circulation of predominantly influenza B viruses, while Colombia and Bolivia experience circulation of predominantly influenza H1N1 (2009) viruses. In most countries of the region, overall influenza virus transmission has declined substantially or returned to very low levels.

Limited data from the tropical areas of sub-Saharan Africa suggest that overall influenza activity has remained low. Since late spring and late summer, there has been persistent low levels of circulation of seasonal influenza A(H3N2) viruses in Kenya and Madagascar, respectively. A similar, but brief period of late summer circulation of seasonal influenza A(H3N2) viruses was also observed in Tanzania. More recently, since late September 2010, Cameroon, in central Africa, has also begun to detect significant level of seasonal influenza A(H3N2) viruses. In contrast, little influenza activity has been reported in West Africa during recent months.

Countries in the temperate zone of the Northern Hemisphere

In Canada and the United States, rates of ILI have increased slightly, but remain at or below seasonal baselines; small numbers of seasonal influenza A(H3N2) and B viruses have been detected during the past month.

Most countries in the European Region continued to report low overall levels of ILI activity, with sporadic detections of influenza A(H3N2), H1N1 (2009) and influenza B viruses.

Overall influenza activity remains sporadic in Northern China, Japan, and South Korea.

Virological surveillance

The WHO Global Influenza Surveillance Network is constantly monitoring the evolution of influenza viruses. Like other influenza viruses, the influenza H1N1 (2009) viruses have being undergoing genetic evolution. Since their emergence, variants having substitutions at residues 125/142, 222 and/or 374/391 in the haemagglutinin gene have been detected. Recently other genetic mutations have also been reported. However, antigenic characterization to date has shown that all these viruses are not antigenically distinguishable from the vaccine virus A/California/7/2009.

FluNet reports

During weeks 41 to 42 (10 -23 October, 2010), National Influenza Centres (NICs) from 31 countries reported data to FluNet*. A total of 1,749 specimens were reported as positive for influenza viruses, 1,512 (86.4%) were typed as influenza A and 237 (13.6%) as influenza B. Of the sub-typed influenza A viruses reported, 15.6% were influenza H1N1(2009) and 84.0 % were influenza A(H3N2).

Influenza virus detection by type/subtype in countries:

  • Influenza H1N1 (2009): Argentina, Australia, Bangladesh, Bolivia, Cambodia, Cameroon, Canada, China, China Hong Kong SAR, Central African Republic, Chile, Columbia, India, Japan, Kenya, Mali, Nigeria, Oman, Paraguay, Republic of Korea, Senegal, Singapore, South Africa, Thailand and United States of America.
  • Influenza A(H3N2): Argentina, Australia, Bangladesh, Bolivia, Cambodia, Cameroon, Canada, Chile, China, China Hong Kong SAR, Columbia, Costa Rica, Cuba, Greece, Jamaica, Japan, Kenya, Madagascar, Mexico, Nigeria, Paraguay, Republic of Korea, Rwanda, Senegal, Singapore, South Africa, Thailand, United Republic of Tanzania and United States of America.
  • Influenza B: Algeria, Argentina, Australia, Bolivia, Cambodia, Cameroon, Canada, Chile, China, China Hong Kong SAR, Columbia, Costa Rica, Cuba, Germany, Guatemala, Honduras, India, Israel, Jamaica, Japan, Kenya, Nicaragua, Nigeria, Paraguay, Republic of Korea, Senegal, Singapore, Slovakia, South Africa, Switzerland, Thailand and United States of America.
  • No influenza activity reported: Angola, Austria, Azerbaijan, Belgium, Bulgaria, Costa Rica, Czech Republic, Denmark, Dominican Republic, El Salvador, Estonia, Ethiopia, Finland, France, Georgia, Ghana, Hungary, Kazakhstan, Kyrgyzstan, Latvia, Luxembourg, Mozambique, Netherlands, Norway, Panama, Poland, Republic of Moldova, Romania, Serbia, Slovenia, Spain, Sweden, Tunisia, Turkey and Uzbekistan

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

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