Global Alert and Response (GAR)

Pandemic (H1N1) 2009 - update 79

Weekly update

As of 13 December 2009, worldwide more than 208 countries and overseas territories or communities have reported laboratory confirmed cases of pandemic influenza H1N1 2009, including at least 10582 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 data.

Situation update:

In the temperate zone* of the northern hemisphere, transmission of pandemic influenza virus remains active and geographically widespread, however disease activity has peaked or passed its peak in many places, particularly North America. Influenza activity continues to increase in later affected areas of south-eastern and central Europe, and in central and south Asia.

In United States and Canada, active influenza transmission persists but overall levels of ILI** have declined substantially to near seasonal baselines. In the US, proportional mortality due to pneumonia and influenza (P&I mortality) has remained consistently elevated above the epidemic threshold for the past 10 weeks; however, weekly numbers of lab-confirmed hospitalizations and deaths continue to decline over the past month.

The preliminary analysis of data from Northern Hemisphere countries that have now passed through an entire season of winter transmission indicate that the mortality rate, as expressed in fatal cases per million people, is in the same range as that which was observed in the Southern Hemisphere winter. This would indicate that the overall severity of the pandemic has not changed although the proportion of the population infected has been much higher in the temperate countries of the Northern Hemisphere during their winter season compared to the circulation observed in their summer season.

In Europe, geographically widespread and active transmission of pandemic influenza virus continued to be observed across the continent. At least 10 countries, mostly in western and northern Europe, reported declining respiratory disease activity. During the last reporting period, ILI/ARI activity continued to increase or reach a plateau in a limited number of countries: the Czech Republic, Estonia,, Hungary, Montenegro and Switzerland (a range of 28-71% of sentinel respiratory samples were positive for influenza in these countries). A high intensity of respiratory disease activity was reported in parts of northern and south-eastern Europe and in parts of the Russian Federation. 99% of subtyped influenza A viruses in Europe were pandemic H1N1 2009. Detections of RSV in Europe continued to increase over the past five weeks, partially accounting for elevated ILI activity among young children in some countries.

In Western and Central Asia, influenza transmission remains active. ILI/ARI activity continues to increase in Kazakhstan and Kyrgyzstan, and has peaked in some countries including in Afghanistan, Oman, and Israel. Influenza virus continues to circulate in Iran, Iraq, Jordan, Egypt and in much of the surrounding region but may have recently peaked in some parts.

In East Asia, influenza transmission remains active but appears to be declining overall. Influenza activity has recently peaked and begun to decline in Japan. ILI activity continued to decline but remained elevated in northern and southern China, Chinese Taipei and in Mongolia. In southern Asia, influenza activity continues to increase in the northern parts of India, Nepal, Sri Lanka, and the Maldives.

In the tropical region of Central and South America and the Caribbean, influenza transmission remains geographically widespread but overall disease activity has been declining.

Pandemic H1N1 2009 virus appears to be the predominant influenza virus circulating in northern and eastern Africa. In West Africa, a mixture of pandemic and seasonal influenza viruses have been detected. Seasonal viruses have included both seasonal H1N1 and H3N2, with the later predominating.

In the temperate region of the southern hemisphere, sporadic cases of pandemic influenza are being reported without evidence of sustained community transmission.

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)

Qualitative indicators (Week 29 to Week 49: 13 July - 6 December 2009)

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 13 December 2009

The countries and overseas territories/communities that have newly reported their first pandemic (H1N1) 2009 confirmed cases since the last web update (No.78): 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 78): Bahamas, Bosnia & Herzegovina, Estonia, Montenegro, Libyan Arab Jamahiriya.

* No update since web update no. 78

** 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.

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