Influenza

Influenza update - 22 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 121

19 November 2010 - Summary:

Worldwide, influenza activity remains low, except in limited areas of tropical Asia and temperate South America. Although the winter influenza season in the temperate zone of the Southern Hemisphere formally concluded during early October 2010 and generally transmission has been negligible since then, there have been recent reports of localized, late season epidemic influenza activity in Argentina, most notably in several provinces in the northwestern part of the country. As the temperate zone of the Northern Hemisphere enters the late autumn and winter months, influenza activity remains at or below seasonal baseline in most countries of Europe, North America, and temperate Asia. Seasonal influenza B and A(H3N2) viruses continue to co-circulate worldwide, with the later slightly predominant; influenza H1N1 (2009) virus circulation continues to be detected at low to moderate levels across Asia, and sporadically in other parts of the world.

Countries in the temperate zone of the Southern Hemisphere

In most countries of the temperate zone of the Southern Hemisphere, influenza virus circulation remained low to sporadic and ILI activity levels remained near or below baseline. In Argentina, however, there have been recent reports of localized, late season epidemics of influenza occurring during September and October 2010 in the several northwestern and far southern provinces. These outbreaks have been associated with circulation of influenza A viruses (some isolates have been characterized as seasonal influenza A(H3N2) but most have not been subtyped). In neighboring Chile, overall influenza activity remained low through late October 2010 after a recently concluded influenza season characterized by a predominance of circulating seasonal influenza A(H3N2) viruses. In South Africa, small numbers of influenza B viruses continued to be detected as the winter influenza season came to an end. In Australia, low level co-circulation of influenza B and H1N1 (2009) viruses continued to be detected through early November 2010 as levels of ILI remained low.

Countries in the tropical zone

Several countries of Southeast Asia continued to report active circulation of influenza viruses. In Thailand, as of mid to late October 2010, there continued to be reports of active but declining co-circulation of seasonal influenza A(H3N2), B, and influenza H1N1 (2009) viruses. In neighboring Cambodia, since September 2010, there has been sustained active circulation of predominantly seasonal A(H3N2) viruses, but also to a lesser extent, seasonal influenza B and H1N1 (2009). In Hong Kong SAR (China), small numbers of seasonal influenza A(H3N2) viruses continue to be detected as levels of ILI have largely returned to seasonal levels after a recently concluded period of epidemic influenza activity. In Singapore, sustained co-circulation of seasonal influenza and H1N1 (2009) viruses has been observed, in varying proportions over time, since April 2010; levels of ARI have remained within the expected seasonal range over past two months. Elsewhere in Asia, Sri Lanka has reported a recent increase in the circulation of seasonal influenza A(H3N2), B, and H1N1 (2009) viruses, while in both Bangladesh and India, influenza activity appears to have significantly subsided after a period of persistent influenza virus circulation since March and June 2010, respectively.

In most countries in the tropics of the Americas, influenza activity has largely subsided. This comes after a period of variable influenza virus transmission spanning late July through early October 2010 during which many countries in the region observed active circulation of seasonal A(H3N2) viruses, while a few noted either seasonal influenza B or H1N1 (2009) activity. More recently, during October 2010, low to moderate levels of influenza A(H3N2) and H1N1 (2009) viruses have been detected in parts of Bolivia and Colombia, respectively.

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. During late September through mid-October 2010, Cameroon, in central Africa, has also begun to detect significant levels of seasonal influenza A(H3N2) and B viruses. In contrast, little influenza activity has been reported in West Africa during recent months, except in Togo, which has recently reported small numbers of H1N1 (2009) virus detections.

Countries in the temperate zone of the Northern Hemisphere

In Canada and the United States, overall influenza activity and levels of ILI remained near or below baseline; 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.

As of late October 2010, overall influenza activity remained low to sporadic in China and Japan. In both, seasonal influenza A(H3N2) viruses were detected at low levels during October 2010.

Human infections with other influenza viruses:

Swine-origin H3N2 virus infection in the US

On 12 November, 2010, the United States Centers for Disease Control and Prevention (US CDC), reported two sporadic cases of human infection with triple reassortant swine origin influenza A(H3N2) viruses. The two cases occurred in separate states, are not believed to be epidemiologically linked to each other, and both occurred in the vicinity of live pigs. Both patients have fully recovered from their illness. The viruses isolated from both patients had some genetic differences further suggesting that two cases were not linked. Investigations thus far have not shown any evidence of community transmission of these viruses. For more information visit: http://www.cdc.gov/flu/weekly/pdf/External_F1044.pdf or http://www.cdc.gov/media/subtopic/heard.htm

The first detection in a human of the triple reassortant swine A(H3N2) virus was in 2005 in Ontario Canada. Since then human cases have been reported nearly every year. All cases have fully recovered and no increased severity has been associated with the infection with these viruses in humans

In North America, A(H3N2) viruses in pigs emerged around 1998-99, when the human influenza A(H3N2) viruses entered into swine population and reassorted with other influenza viruses already circulating in pigs. The A(H3N2) viruses currently circulating in the swine population in US and Canada contain gene segments from avian-like, swine-like, and human-like viruses.

Early identification and investigation of human infections with novel influenza A viruses is critical to evaluate the extent of the outbreak and possible human-to-human transmission and WHO continues to encourage member states to investigate and report these events.

H5N1 case in Hong Kong

On 17 November 2010, the Department of Health of Hong Kong SAR, China, reported a confirmed human case of influenza A(H5N1) virus infection to WHO. The case has a travel history to Shanghai, Nanjing and Hangzhou. The investigation is still ongoing but based on current information this is a sporadic case of human infection with influenza A(H5N1) virus without secondary spread. See also http://www.who.int/csr/disease/avian_influenza/en/index.html

Virological surveillance

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

On November 5, 2 cases of human infection with swine-origin triple reassortant A(H3N2) viruses were reported by CDC through IHR.

FluNet reports

During weeks 43 to 44 (24 October to 6 November 2010), National Influenza Centres (NICs) from 43 countries reported data to FluNet*. A total of 1,442 specimens were reported as positive for influenza viruses, 1,123 (77.9%) were typed as influenza A and 313 (21.7%) as influenza B. Of the sub-typed influenza A viruses reported, 23.8% were influenza H1N1(2009) and 75.5% were influenza A(H3N2).

Influenza virus detection by type/subtype in countries:

  • Influenza H1N1 (2009): Australia, Bolivia, Brazil, Cambodia, Cameroon, China, China Hong Kong SAR, Fiji, Ghana, Guadeloupe, Ireland, Japan, Kenya, Lao People's Democratic Republic, Norway, Singapore, South Africa, Sri Lanka, Togo and United States of America.
  • Influenza A(H3N2): Algeria, Australia, Bolivia, Brazil, Cambodia, Cameroon, Canada, Chile, China, China Hong Kong SAR, Costa Rica, Cuba, Fiji, French Guiana Ghana, Ireland, Japan, Kenya, Madagascar, Mexico, Mongolia, Norway, Republic of Korea, Singapore, South Africa, United Kingdom and United States of America.
  • Influenza A(H1N1): China
  • Influenza B: : Algeria, Australia, Bolivia, Brazil, Cambodia, Cameroon, Canada, Chile, China, China Hong Kong SAR, Costa Rica, Cuba, El Salvador, Honduras, Ireland, Kenya, Lao People's Democratic Republic, Norway, Singapore, South Africa, Sri Lanka, Togo, United Kingdom and United States of America.

Afghanistan, Denmark, Estonia, Ethiopia, Finland, France, Greece, Iran (Islamic Republic of), Martinique, Morocco, Poland, Republic of Korea, Romania, Russian Federation, Slovenia, Spain, Switzerland and Tunisia reported no influenza activity.

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

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