H1N1 2009 virus continues to circulate

13 September 2009

In the latest weekly update the World Health Organisation (WHO) reports that in the temperate region of the southern hemisphere (represented by countries such as Chile, Argentina, Australia, New Zealand, and South Africa), influenza activity continues to decrease or return to baseline.

Active transmission persists in tropical regions of the Americas and Asia. Many countries in Central America and the Caribbean continue to report declining activity for the 2nd week in a row.  However, countries in the tropical region of South America (represented by countries such as Bolivia, Ecuador, and Venezuela) are reporting increasing levels of respiratory disease.

In the tropical regions of Asia, respiratory disease activity remains geographically regional or widespread but the trend is generally increasing as noted in India, Bangladesh, and Cambodia.

In the temperate regions of the Northern Hemisphere activity is variable. In the United States, regional increases in influenza activity are being reported, most notably in the south-eastern states.  Most of Europe is reporting low or moderate respiratory diseases activity, but parts of Eastern Europe are beginning to report increases in activity.

WHO Collaborating Centres and other laboratories continue to report sporadic isolates of oseltamivir-resistant influenza virus. 21 such virus isolates have now been described from around the world, all of which carry the same mutation that confers resistance to the antiviral oseltamivir but not to the antiviral zanamivir. Of these, 12 have been associated with post-exposure prophylaxis, 4 with long term oseltamivir treatment in patients with immunosuppression. Worldwide, more than 10 000 isolates of the pandemic (H1N1) 2009 virus have been tested and found to be sensitive to oseltamivir. WHO will continue to monitor the situation closely in collaboration with its partners, but is not changing its guidelines for use of antiviral drugs at this time.

Pandemic (H1N1) 2009 influenza virus continues to be the predominant circulating virus of influenza, both in the northern and southern hemisphere.

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