WHO: Pandemic (H1N1) 2009 - update 66

Weekly update

In the temperate regions* of the northern hemisphere, influenza activity remains widely variable. In North America, the United States is reporting increases in influenza-like-illness activity above the seasonal baseline, most notably in the southern, southeastern, and parts of the northeastern United States.

In Canada, influenza activity remains low. In Europe and Central Asia influenza activity remains low overall, except in France, which is reporting increases in influenza-like-illness activity (for week 37) above the seasonal epidemic threshold. Geographically localized influenza activity is being reported in several countries (Austria, Georgia, Ireland, Luxembourg, Norway, Portugal, the Czech Republic, Cyprus, and Israel). In Japan, influenza activity remains stably increased above the seasonal epidemic threshold with the most notable increases being reported on the southern island of Okinawa.

In the tropical regions of the Americas and Asia, influenza transmission remains active. Geographically regional to widespread influenza activity continues to be reported throughout much of South and Southeast Asia, with increasing trends in respiratory diseases being reported in India and Bangladesh. Geographically regional to widespread influenza activity continues to be reported for the tropical regions of Central and South America without a consistent pattern in the trend of respiratory diseases (continued increases are being reported in Bolivia and Venezuela).

In the temperate regions* of the southern hemisphere, influenza activity continues to decrease or has returned to the seasonal baseline in most countries. In Australia, later affected areas are also now reporting declining levels of influenza-like-illness. In South Africa, influenza activity appears to have recently passed over the second peak (the first peak was due to seasonal influenza A (H3N2) and second peak was due to pandemic (H1N1) 2009).

WHO Collaborating Centres and other laboratories continue to report sporadic isolates of oseltamivir resistant influenza virus. Twenty six such virus isolates have now been described from around the world, all of which carry the same H275Y mutation that confers resistance to the antiviral oseltamivir but not to the antiviral zanamivir. Of these, 12 have been associated with post-exposure prophylaxis, five with long term oseltamivir treatment in patients with immunosuppression. Worldwide, over 10,000 clinical samples and 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.

Pandemic (H1N1) influenza virus continues to be the predominant circulating influenza virus, both in the northern and southern hemisphere. See below for detailed laboratory surveillance update.

*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.

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