Influenza

Influenza update - 3 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 122

3 December 2010 - Summary:

Worldwide, influenza activity remained low, except in areas of South Asia and central and western Africa, which have seen recent surges in influenza H1N1 (2009) virus detections. As the northern hemisphere winter approaches, with few exceptions, most countries in the temperate zone of the northern hemisphere continued to report low levels of ILI and influenza virus detections. Except for a few countries in Southeast Asia, most countries in the tropics of the Americas and Asia have recently reported low levels of influenza activity. Globally, there continued to be co-circulation of influenza H1N1 (2009), A(H3N2), B viruses, with the latter two being predominant.

Countries in the temperate zone of the Northern Hemisphere

In North America, overall influenza activity and levels of ILI remained below baseline. Notably, however, in the southeastern part of the United States, influenza activity has steadily increased over the month of November 2010; in the southwestern region, as of the third week of November, approximately 17% of respiratory specimens tested positive for influenza, including both influenza A(H3N2) and B viruses, with the later being predominant.

Most countries of the European region continued to report low overall levels of ILI and low to sporadic levels of influenza virus detections. In Bulgaria and the Russian Federation, a medium intensity of respiratory diseases activity was reported, however, it is not yet known if these increases were associated with circulation of influenza viruses.

In East Asia, overall influenza activity remained low across China, Japan, and the Republic of Korea. In northern China, the number of respiratory specimens testing positive for influenza (primarily influenza A(H3N2)) increased between late October and mid-November 2010, however, the increase in the detection rate was associated with only a small rise the levels of ILI. In Mongolia, during mid to late November 2010, reported an increase in the detection rate of influenza A(H3N2) viruses which was associated with an increase in the rate of ILI above the seasonal threshold, suggesting that local winter influenza season has begun.

Countries in the temperate zone of the Southern Hemisphere

Overall, little influenza activity is being reported as the summer months approach in countries of the temperate Southern Hemisphere. Late season and regionally variable epidemics of influenza A(H3N2) virus in Chile and Argentina now appear to have largely subsided. In South Africa, influenza activity has also largely subsided after a period of low level springtime circulation of influenza B and H1N1 (2009) viruses detected in the sentinel ILI surveillance system during November 2010.

Countries in the tropical zone

In South Asia, only Sri Lanka reported a recent surge of influenza H1N1 (2009) virus detections during mid-October through late November 2010, however, to date there have not been reports of unusual clinical severity of cases. In India and Bangladesh, influenza activity observed during recent months has now largely subsided.

In Southeast Asia, several countries continued to report low to moderate levels of influenza A(H3N2) virus detections.

In Sub-Saharan Africa, overall influenza activity remained low in most countries, except in Cameroon and Ethiopia, which as of early to mid-November 2010, reported a recent surge in the numbers of specimens testing positive for H1N1 (2009) virus [18(69%) of 26 specimens testing positive in Ethiopia and 18(23%) of 79 specimens testing positive in Cameroon]. The extent to which these increased detections of influenza virus have been associated with increased ILI in the community is not yet known. Across the rest of the region, low to moderate levels of influenza A(H3N2) virus circulation continued to be detected in Kenya and Ghana, respectively.

In the tropical zone of the Americas, overall influenza activity remained low to sporadic in most areas. In Costa Rica, influenza A(H3N2) and B viruses continued to co-circulate at low levels during November 2010. In Columbia, small numbers of influenza H1N1 (2009) viruses were detected during November 2010. In Bolivia, sustained active circulation of influenza A(H3N2) viruses has been observed since mid-September 2010. In Cuba, there has been a fluctuating low to moderate level circulation of influenza A(H3N2) viruses since early August 2010. In southern Mexico, influenza activity has largely subsided after a period of active influenza A(H3N2) circulation spanning August to mid-November 2010.

Virological surveillance

In general, influenza virus activity remained low worldwide, with influenza A(H3N2) predominating.

FluNet reports

During weeks 45 to 46 (7 to 20 November 2010), National Influenza Centres (NICs) from 52 countries reported data to FluNet*. A total of 1,299 specimens were reported as positive for influenza viruses, 932 (71.7%) were typed as influenza A, 367 (28.3%) as influenza B. Of the sub-typed influenza A viruses reported, 29.5% were influenza H1N1(2009) and 69.6% were influenza A(H3N2). In addition, very few old seasonal A(H1N1) viruses were detected and one A(H5N1) virus infection in human was confirmed by laboratory.

Influenza virus detection by type/subtype in countries:

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

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

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