Emergencies preparedness, response

Pandemic (H1N1) 2009 - update 102

Weekly update

As of 23 May, worldwide more than 214 countries and overseas territories or communities have reported laboratory confirmed cases of pandemic influenza H1N1 2009, including over 18114 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:

The most active areas of pandemic influenza virus transmission currently are in parts of the Caribbean and Southeast Asia, where low level circulation is occurring. Except for localized areas of pandemic influenza activity in parts of Chile, there is little evidence of pandemic influenza activity in the temperate zone of the southern hemisphere. Of note, Respiratory Syncitial Virus (RSV) is widely circulating in South America resulting in an increase in respiratory disease activity, complicating somewhat the interpretation of syndromic surveillance data from the area. RSV primarily affects children under the age of 5 years. Seasonal influenza A viruses continue to be detected at low to sporadic levels in all regions. Influenza B has been reported in increasing but low numbers in South America, where it only recently appeared, while it is decreasing in Asia.

In the Caribbean and Central America, Cuba and to a much lesser extent Costa Rica, continue to experience active circulation of pandemic influenza virus. In Cuba, current pandemic influenza activity, which began during late February 2010, remains unchanged since reaching a plateau during mid-April 2010; in addition, over the past month, there have been sporadic detections of seasonal influenza B viruses and also evidence of co-circulation of other respiratory viruses. In Costa Rica, sustained low levels of pandemic influenza virus have been co-circulating with other respiratory viruses since the beginning of 2010. Several other countries in the region continue to report sporadic detections of seasonal influenza B viruses and low level co-circulation of other respiratory viruses.

In the tropical zone of South America, pandemic and seasonal influenza viruses continued to circulate at low to sporadic levels. In Peru, recent regional increases in respiratory diseases activity (in children under age 5) has been largely associated with circulating respiratory syncitial virus (RSV). In Colombia and Brazil, low levels of pandemic and seasonal influenza H3N2 viruses have been detected over the past month. In Bolivia, a recent period of circulation of predominantly seasonal influenza type B viruses appears to have concluded.

In Asia, overall pandemic influenza activity remains low to sporadic, except in limited areas of south and southeast Asia, particularly Singapore, Malaysia, and Bangladesh. In Singapore, levels of ARI have been elevated since April 2010 and in recent weeks have remained near epidemic threshold; approximately 39% of respiratory specimens from ILI patients tested positive for pandemic influenza virus during mid May 2010. In neighboring Malaysia, limited data suggest that active pandemic influenza virus circulation persist after recent activity peaked during mid April 2010; small numbers of fatal cases have been reported since that time. In Bangladesh, co-dominant circulation of pandemic and seasonal influenza B viruses has been observed since mid April 2010, however, the overall intensity of respiratory diseases was reported to low during this period. Low levels of pandemic influenza virus continued to circulate in western India, while low and declining levels of seasonal influenza B viruses continued to be reported across East Asia.

In Sub-Saharan Africa, limited data from several countries continues to suggest that active transmission of pandemic influenza virus in West Africa has now largely subsided. In addition to the persistence of low level circulation of pandemic influenza virus in Ghana, sporadic detections of pandemic influenza virus have been reported during the past month in Cameroon, Angola, and Rwanda. In Cameroon, there has been persistent active circulation of seasonal influenza B viruses since mid-March 2010.

In the temperate regions of the northern and southern hemisphere, overall pandemic influenza activity remains low to sporadic. In southern hemisphere, Chile continues to report increased ILI in several regions of the country (notably Los Lagos), however, the increase in respiratory disease activity has been predominantly associated with circulating RSV and only to a much lesser extent pandemic influenza virus. In neighboring Argentina, Paraguay, and Uruguay, all recent respiratory diseases activity during the past month has been associated with viruses other than influenza. Similarly, there have been no recent detections of influenza virus in South Africa. In New Zealand and Australia, overall levels of ILI remain low; only sporadic detections of seasonal influenza H3N2 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).

  • Weekly update (Virological surveillance data)
    As of May 12 May 2010, 4 additional cases of oseltamivir resistant pandemic influenza A (H1N1) 2009 viruses have been reported. It brings the cumulative total to 289 so far. All but one of these have the H275Y substitution and are assumed to remain sensitive to zanamivir.

*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
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    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 19: 13 July 2009 - 15 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 23 May 2010

The countries and overseas territories/communities that have newly reported their first pandemic (H1N1) 2009 confirmed cases since the last web update (No. 101): 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. 101): 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