WHO | Pandemic (H1N1) 2009 - update 98

Pandemic (H1N1) 2009 - update 98
Weekly update
30 April 2010 -- As of 25th of April, worldwide more than 214 countries and overseas territories or communities have reported laboratory confirmed cases of pandemic influenza H1N1 2009, including over 17919 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 transmission of pandemic influenza H1N1 virus continue to be parts of West and Central Africa with some focal areas of activity in South and Southeast Asia. Pandemic influenza activity H1N1 remains low in much of the temperate areas of both the northern and southern hemispheres. Seasonal influenza type B virus is the predominant influenza virus, though also at low levels of circulation, across East Asia, Northern and Eastern Europe. Influenza type B viruses have also been detected in Central Africa and this week in West Africa. Seasonal influenza H3N2 viruses have continued to be detected in South and Southeast Asia, as well as sporadically in some countries of West and Central Africa, and Eastern Europe.

In Sub-Saharan Africa, data from a limited number of countries suggests that active transmission of pandemic influenza H1N1 virus is declining across West and West-central Africa. Ghana is reporting moderate amounts of pandemic virus (16 % of all clinical specimens tested were positive for pandemic influenza) but smaller numbers of cases continue to be detected in Senegal, Niger and Cameroon. In East Africa, influenza activity has returned to low levels. Only Rwanda has detected small numbers of pandemic virus in the past week. In addition, a few seasonal influenza H3N2 viruses are seen in Ghana. Influenza type B has been increasingly detected in the area, notably in Ghana and Cameroon.

In East Asia, pandemic influenza H1N1 virus circulation is now sporadic. In China, Mongolia, and Republic of Korea most influenza like illness cases continued to be primarily due to seasonal influenza type B viruses. In China and Mongolia influenza detections have continued to decline compared to previous recent weeks. The Republic of Korea reported increasing levels of respiratory disease activity associated with increasing detections of seasonal influenza type B in respiratory specimens over five consecutive weeks. Of note, small numbers of pandemic influenza H1N1, seasonal H3N2 and H1N1 viruses continued to be sporadically detected in some countries of the region.

In Southeast Asia, overall levels of influenza activity were low. Although the predominant influenza virus circulating was still pandemic influenza H1N1, there was co-circulation of seasonal influenza type B and, to a lesser extent, H3N2 viruses in several countries including Singapore, Cambodia, Indonesia and Thailand. Malaysia has reported increasing levels of respiratory diseases activity associated with pandemic influenza H1N1 laboratory confirmed cases. Media sources have also reported school closures in the country. In Singapore, influenza-like-illness levels are still below the seasonal epidemic threshold but have increased compared to previous week.

In South Asia, Bangladesh reported an increase in respiratory diseases activity associated with increasing numbers of pandemic influenza H1N1 laboratory confirmed cases since beginning of April. India reported pandemic influenza activity in the states of Maharashtra and recently Karnataka. Levels of respiratory diseases activity in both of these countries appear much less intense than in the initial wave of transmission which occurred late 2009. Although pandemic influenza is the predominant virus circulating in the region, seasonal influenza type B viruses continued to be detected in Iran and Bangladesh.

In the tropical zone of the Americas, limited data suggested that pandemic influenza H1N1 activity remains low but with a few localized areas of transmission. Jamaica, Panama and Guatemala, reported increasing trends in respiratory disease activity. In Cuba, all provinces reported an increase in numbers of acute respiratory diseases cases in the last two weeks, mainly from the city of Havana. In Peru, the number of pneumonia cases in children under 5 years of age in Lima has been increasing since six consecutive weeks and remained above the epidemic threshold. However, the extent to which these pneumonia cases have been due to pandemic influenza H1N1 virus is not known. Notably, respiratory syncitial virus (RSV) has been reported to be circulating in the area.

In the temperate zone of the Northern Hemisphere, overall pandemic influenza H1N1 activity remained low. In United States, the proportion of outpatient visits for influenza-like illness was below the national baseline. No influenza B is reported by countries of North America. In Europe, pandemic influenza activity is at very low intensity in all countries. The overall proportion of sentinel respiratory samples testing positive for influenza remained stable at about 4.5%. For the current week, the total number of sentinel influenza B detections continued to exceed that of influenza A, mainly due to viral detections from Eastern Europe: Central, Siberian, Far Eastern regions of the Russian Federation and Kazakhstan.

In the temperate countries of the Southern Hemisphere, influenza-like illness activity remained low and at the levels experienced at the same time in previous years. Australia has continued to report sporadic detections of pandemic influenza H1N1, seasonal influenza B and H3N2 viruses in low numbers in recent weeks.

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).

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WHO | Pandemic (H1N1) 2009 - update 98