Emergencies preparedness, response

Pandemic (H1N1) 2009 - update 101

Weekly update

21 May 2010 - As of 16 May, worldwide more than 214 countries and overseas territories or communities have reported laboratory confirmed cases of pandemic influenza H1N1 2009, including over 18097 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 current situation is largely unchanged since the last update. The most active areas of pandemic influenza virus transmission currently are in parts of the Caribbean and Southeast Asia. In the temperate zone of the northern and southern hemisphere, overall pandemic influenza activity remains low to sporadic. In central Africa, there has been increased transmission of seasonal influenza type B viruses, accounting for 85% of all influenza isolates in the region. Influenza B also continues to be detected at low levels across parts of Asia and Europe, and has now been reported in Central America.

In the tropical region of the Americas, the most active areas of pandemic influenza virus transmission continue to be in parts of the Caribbean. In Cuba, a second period of active community transmission of pandemic influenza virus began during late February 2010, peaked during late April 2010, and has been declining since; this second period of transmission, although associated with severe and fatal cases, appears to be less intense overall than the first period of transmission which occurred during late September to late November 2009. In contrast, in the Dominican Republic, low to moderate intensity of respiratory diseases activity has been primarily associated with co-circulation of respiratory viruses other than influenza; only sporadic detections of seasonal influenza viruses have been reported. Low levels of pandemic influenza viruses have been circulating across parts of Central America and tropical areas of South America, for example, in Mexico since December 2009, in Colombia and Brazil since early 2010, and in Guatemala since early April 2010. Nicaragua and Honduras have also been recently reporting geographically regional spread of influenza viruses, however, the relative proportions of seasonal influenza, pandemic influenza, and other respiratory virus detections are not known. In contrast, in Panama, low levels of respiratory disease over the past three months have been primarily associated with circulating respiratory viruses other than influenza. Of note, Bolivia experienced a recent period of low but sustained transmission of seasonal influenza type B viruses between late February and early May 2010. There continues to be evidence from several countries in this region that there is ongoing co-circulation of influenza with other respiratory viruses (including respiratory syncytial virus (RSV), and adenovirus).

In Asia, the most active areas of pandemic influenza virus transmission are in parts of South and Southeast Asia, particularly in Bangladesh, Malaysia, and Singapore. In Malaysia, limited data suggests that a second period of active pandemic influenza virus transmission has been occurring since early April 2010, but overall activity may have recently stabilized and does not appear to exceed pandemic influenza activity seen during an earlier period of transmission lasting from July until early September 2009. In Singapore, levels of ARI have remained elevated since mid April 2010; during the most recent reporting week, levels of ARI exceeded the epidemic threshold and the proportion of patients with ILI testing positive for pandemic influenza virus infection was 39%. In Bangladesh increased co-circulation of pandemic influenza and seasonal influenza type B viruses has been detected since mid April 2010 but now appears to have stabilized. Low level circulation of pandemic influenza continues to persist in Thailand and in the western and southern parts of India; sporadic detection of pandemic influenza continue to be reported in Cambodia and in the Philippines. In East Asia, only sporadic detections of pandemic influenza virus are being reported; seasonal influenza type B viruses have been predominant in this region, however circulation appears to be declining in China and the Republic of Korea.

In the temperate regions of the northern and southern hemisphere, overall pandemic influenza activity remains low to sporadic. In Australia and New Zealand, slight increases in ILI activity were reported; however, in Australia, these increases have been attributed primarily to circulating respiratory viruses other than influenza. In the southern temperate regions of the Americas, only sporadic detections of influenza viruses have been reported, except in Chile, which continues to report localized areas of increased ILI activity (in the Los Lagos area) associated with co-circulation of pandemic influenza and other respiratory viruses. In Europe, very low to sporadic levels of pandemic and seasonal influenza type B viruses continue to be detected. Seasonal influenza type B virus persists mainly in parts of eastern and northern Europe. Georgia reported an increase in the number of respiratory disease consultations due to influenza-like-illness (ILI), mainly in children (under age 5) and school-age children (5-14 years old age group); whether this increase is associated with pandemic influenza A (H1N1) virus is not yet known.

In Sub-Saharan Africa, limited data from several countries suggest that active transmission of pandemic influenza virus in West Africa has now largely subsided. In Ghana, 6% of respiratory samples tested positive for pandemic influenza virus during the most recent reporting week. Across the rest of region, the pandemic influenza virus continues to be detected sporadically or at low levels, most recently in Angola and Rwanda. Sporadic detections of seasonal influenza H3N2 and influenza B viruses have been reported in western, central Africa and to a lesser extent southern Africa.

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 (WEEK 18: 25 APRIL - 8 MAY 2010)

  • 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 18: 13 July 2009 - 8 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 16 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. 100): 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. 100): 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