Pandemic (H1N1) 2009 - update 105

Pandemic (H1N1) 2009 - update 105

The situation remains largely unchanged since the last update. Overall pandemic influenza activity remains low worldwide with geographically limited circulation of pandemic influenza virus in parts of the tropics, particularly in parts of Central America and the Caribbean and in parts of South and Southeast Asia. Seasonal influenza type B viruses continue to circulate at low levels across Asia and to a lesser extent across parts of Africa and South America. Recently re-emerged seasonal influenza H3N2 viruses continue to circulate in East Africa. As countries of the temperate southern hemisphere enter winter, overall only sporadic influenza activity has been detected so far.

In tropical region of the Americas, low or waning circulation of pandemic virus has been primarily reported in Costa Rica (since early 2010) and in Cuba (last reported at the end of May 2010), respectively. In Cuba and to a lesser extent in Costa Rica, recent pandemic influenza activity has been associated with small numbers of fatal cases. In Colombia, during the first week of June 2010, an increasing trend of respiratory diseases was associated with regional spread of pandemic influenza activity and a small number of new fatal cases, likely reflecting increasing but low level circulation of pandemic influenza virus. Throughout the rest of the region, there have been only sporadic detections of pandemic influenza virus during the past month. In several countries of the region, there has been recent circulation of seasonal influenza viruses including type A (Venezuela since May 2010) and B (Bolivia since March 2010). Throughout the region there has been variable ongoing co-circulation of other respiratory viruses, particularly RSV.

In Asia, pandemic influenza virus continues to actively circulate in Malaysia, Singapore, and to a much lesser extent in parts of India, Bangladesh, and Bhutan. In Malaysia, limited data suggest that virus transmission persists but continues to decline; the number of new cases reported per week plateaued during mid-April 2010 and began to decline at the end of May 2010. In Singapore, during the second week of June 2010, the levels of ARI remained near the warning level but below the epidemic threshold; approximately 28% of respiratory samples from patients with ILI tested positive for pandemic influenza virus. In South Asia, low level circulation of pandemic influenza virus has persisted in western India (since early 2010) and Bangladesh (since late February 2010); in India but not Bangladesh, regional, low intensity transmission during 2010 has been associated with small numbers of fatal cases over time. Seasonal influenza type B viruses continue to co-circulate with pandemic influenza virus in Bangladesh and have only recently emerged and become predominant in India, although at low levels. Of note, there have been recent media reports of increasing pandemic influenza activity in the southern Indian state of Kerala and more information is expected to become available soon. In Bhutan, there have recent reports of school outbreaks of pandemic influenza virus infection in three separate areas of the country, however, the overall intensity of respiratory diseases in the population was reported to be low.

In Sub-Saharan Africa, pandemic influenza virus continued to circulate at low levels in limited areas of East and West Africa. During the first week of June 2010, 10% and 16% of all respiratory samples tested positive for pandemic influenza virus in Tanzania and Ghana, respectively. Small but significant numbers of seasonal H3N2 viruses continue to be 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. Other respiratory viruses, most notably RSV, are known to be circulating in Chile and Argentina. During first two weeks of June 2010, small numbers of seasonal influenza H3N2 and type B viruses have been detected 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.

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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.