Global Alert and Response (GAR)

Pandemic (H1N1) 2009 - update 104

Weekly update

As of 6 June, worldwide more than 214 countries and overseas territories or communities have reported laboratory confirmed cases of pandemic influenza H1N1 2009, including over 18156 deaths.

WHO is actively monitoring the progress of the pandemic through frequent consultations with the WHO Regional Offices and Member States and through monitoring of multiple sources of information.

Situation update:

Active but declining transmission of pandemic influenza virus persists in limited areas of the tropics, particularly in Southeast Asia and the Caribbean. As countries of the temperate southern hemisphere enter winter, only sporadic influenza activity has been detected so far, except in Chile and Uruguay, both of which have recently reported small numbers of pandemic influenza virus detections. Although seasonal influenza B viruses have been the predominant type of influenza virus circulating worldwide since the end of February 2010, there have been increasing but low level detections of seasonal influenza H3N2 viruses, particularly in South America and in East Africa.

In the tropics of the Americas, overall pandemic influenza activity is low, however, both seasonal influenza H3N2 and type B viruses are actively circulating in parts of tropical South America. Active but declining transmission of pandemic influenza virus continues to be detected primarily in Cuba. Since early 2010, pandemic influenza virus has circulated at low levels in Costa Rica. Sporadic detections of pandemic influenza virus continue to be reported in Brazil. During the most recent reporting week (last week of May 2010), both Brazil and Venezuela reported regional spread of influenza activity associated with an increasing trend of respiratory diseases. In Venezuela, recent influenza activity (which began during early May 2010) has been predominantly due to circulating seasonal influenza A viruses. In Bolivia, circulation of seasonal influenza viruses, predominantly type B, was observed between March and May 2010 and now appears to be subsiding.

In Asia overall pandemic influenza virus transmission remains low, except in parts of tropical South and Southeast Asia, particularly Singapore, Malaysia, and Bangladesh. In Singapore, overall levels of ARI remained slightly below the epidemic threshold and the proportion of respiratory samples testing positive for pandemic influenza virus increased slightly to 34% (during the last week of May 2010). In Malaysia, limited data suggests that pandemic influenza virus transmission has begun to decline since plateauing during May 2010. In Bangladesh, there has been stable persistent low level co-circulation of pandemic and seasonal influenza B viruses since March 2010. Sporadic detections of pandemic influenza virus continued to be reported across other parts of Asia. In East Asia, overall influenza activity remains low, however, seasonal influenza B viruses continue to circulate at low and declining levels.

In Sub-Saharan Africa, pandemic influenza virus continued to circulate at low levels in parts of West Africa, most notably in Ghana. During the most recent reporting week, 13% of all respiratory samples tested positive for pandemic influenza virus in Ghana. Small but significant numbers of seasonal H3N2 viruses have been detected in Kenya and Tanzania since late May 2010.

Overall, in the temperate regions of the northern hemisphere, pandemic influenza viruses have been detected only sporadically during the past month. In the temperate southern hemisphere, only two countries, Chile and Uruguay, have recently reported small numbers of pandemic influenza virus detections. In Chile, there was low level geographically limited circulation of pandemic influenza virus during May 2010; 3.4% of respiratory samples tested positive for pandemic influenza virus during the last week of May 2010. Of note, in Uruguay, 11 (44%) of 25 samples tested positive for pandemic influenza during the most recent reporting week (the last week of May 2010); however, the corresponding intensity of respiratory diseases in the population is not yet known. Other respiratory viruses, most notably RSV, are known to be circulating in Chile and Argentina. There have been no recent detections of pandemic influenza virus in South Africa. In New Zealand and Australia, overall levels of ILI remain low; only sporadic detections of seasonal and pandemic influenza viruses have been recently reported in Australia.

The Global Influenza Surveillance Network (GISN) continues monitoring the global circulation of influenza viruses, including pandemic, seasonal and other influenza viruses infecting, or with the potential to infect, humans including seasonal influenza. For more information on virological surveillance and antiviral resistance please see the weekly virology update (Virological surveillance data, below).

*Countries in temperate regions are defined as those north of the Tropic of Cancer or south of the Tropic of Capricorn, while countries in tropical regions are defined as those between these two latitudes.

**Abbreviations: influenza-like-illness (ILI), acute respiratory infection (ARI), and severe acute respiratory infection (SARI)

MAP OF INFLUENZA ACTIVITY AND VIRUS SUBTYPES (WEEK 21: 23 MAY - 29 MAY 2010)

  • Map of influenza activity and virus subtypes
    png, 256kb

    Description: Displayed data reflect the most recent data reported to Flunet (www.who.int/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 seasonal or pandemic influenza. 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 with similar influenza transmission patterns to be able to give an overview (http://www.who.int/csr/disease/swineflu/transmission_zones/en)

Qualitative indicators (Week 29 to Week 21: 13 July 2009 - 29 May 2010)

The qualitative indicators monitor: the global geographic spread of influenza, trends in acute respiratory diseases, the intensity of respiratory disease activity, and the impact of the pandemic on health-care services.

The maps below display information on the qualitative indicators reported. Information is available for approximately 60 countries each week. Implementation of this monitoring system is ongoing and completeness of reporting is expected to increase over time.

Geographic spread of influenza activity
Trend of respiratory diseases activity compared to the previous week
Intensity of acute respiratory diseases in the population
Impact on health care services
Laboratory-confirmed cases of pandemic (H1N1) 2009 as officially reported to WHO by States Parties to the IHR (2005) as of 6 June 2010

The countries and overseas territories/communities that have newly reported their first pandemic (H1N1) 2009 confirmed cases since the last web update (No. 103): none.

The countries and overseas territories/communities that have newly reported their first deaths among pandemic (H1N1) 2009 confirmed cases since the last web update (No. 103): none.

*The reported number of fatal cases is an under representation of the actual numbers as many deaths are never tested or recognized as influenza related.
**No update since 7 March 2010
***No update since 23 May 2010

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