WHO Update - Pandemic (H1N1) 2009 - update 99 (7 May 2010)

Weekly update
7 May 2010 -- As of 2nd May, worldwide more than 214 countries and overseas territories or communities have reported laboratory confirmed cases of pandemic influenza H1N1 2009, including over 18001 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 most active areas of pandemic influenza virus transmission currently are in parts of West Africa, the Caribbean, and Southeast Asia. In the temperate zone of the northern and southern hemisphere, overall pandemic influenza activity remains sporadic. Seasonal influenza virus type B continues to be detected sporadically across Asia, Africa, Europe, and the Americas, however, low levels of late season virus circulation have primarily detected in East and Central Asia, southern Europe, and central Africa.

In Sub-Saharan Africa, limited data from several countries suggest that active transmission of pandemic influenza virus persists in parts of West Africa while low levels of seasonal influenza type B viruses continue to circulate in parts of central Africa. In Ghana, pandemic influenza virus detections may be declining after peaking during early April 2010; during the most recent reporting week, 14% of respiratory specimens tested positive for pandemic influenza virus. In Cameroon, low levels of pandemic and seasonal influenza type B virus continue to co-circulate, though the latter have been predominant during April 2010. In the Democratic Republic of Congo, circulation of seasonal influenza H3N2 viruses during February and mid-March 2010 has been largely replaced by circulation of seasonal influenza type B viruses during April 2010. Localized, low level pandemic influenza virus circulation continues to be observed in parts of East Africa, particularly in Rwanda and Tanzania. Sporadic detections of seasonal influenza H3N2 viruses continue to be reported across eastern, central, and western Africa.

In tropical zone of the Americas, limited data suggest that pandemic influenza virus transmission remains active in several countries. In Central America, Guatemala reported three consecutive weeks of an increasing trend of respiratory diseases activity associated with regional spread of pandemic influenza virus and detection of severe cases. In Cuba, detections of pandemic virus and numbers of severe cases have increased since late March, however overall pandemic influenza activity may have recently peaked during the most recent reporting week. In Peru, the number of pneumonia cases in children under 5 years of age in the capital area has been increasing for the past seven weeks and remains above the epidemic threshold; however, the extent to which these pneumonia cases have been due to pandemic influenza H1N1 virus versus other respiratory viruses circulating in the region, is not known. Although the overall intensity of respiratory diseases across the region remained low to moderate during April 2010, for short periods of time, circulation of pandemic influenza virus was reported to widespread (in Cuba and Barbados) or regional (in Mexico, Honduras, Nicaragua, Columbia, Venezuela, Brazil, Ecuador and Bolivia).

In Southeast Asia, pandemic influenza virus continues to actively circulate in several countries of the region, however, respiratory disease trends in the region are variable. In Malaysia, limited data suggest that pandemic influenza virus transmission persists with ongoing reports of new cases (including severe cases) and media reports of several school outbreaks, particularly during late April and early May 2010. In Singapore, the national level of ARI has been steadily increasing since early April 2010 and now exceeds the epidemic threshold; 37% of sentinel respiratory specimens tested positive for influenza during the most recent reporting week. In Thailand, the proportion of sentinel outpatients with ILI and sentinel inpatients with pneumonia testing positive for pandemic influenza virus infection has declined significantly since peaking during late March 2010.

In South Asia, the most active area of pandemic influenza virus transmission continues to be in Bangladesh, which continues to report increasing respiratory diseases activity associated with co-circulation of pandemic and seasonal influenza type B viruses since mid April 2010. However, persistent low level co-circulation of both viruses has been detected since late February 2010. In India, localized low level circulation of pandemic influenza virus continues to be detected in parts of western and southern India.

In East Asia, very low levels of pandemic influenza virus continue to be detected. Although overall rates of respiratory illness remain low across the region, recent low levels of influenza activity in a number of countries in the region have been largely due to circulating seasonal influenza type B viruses. Three countries in region, Mongolia, China, and South Korea, each experienced a period of sustained seasonal influenza type B virus circulation following an earlier, generally more intense, wintertime period of pandemic influenza virus transmission. China and South Korea continue observe active but declining levels of seasonal influenza type B virus circulation.

In the temperate zone of the southern hemisphere, overall pandemic and seasonal influenza activity remains sporadic, except in Chile, where there is evidence of low level community circulation of pandemic influenza virus, including detection of small numbers of severe cases; however it too early to know if this signals an early start to wintertime influenza season. The national level of ILI in Chile remained near baseline; however, in at least two southern regions the region specific level of ILI was elevated above baseline, and in one region, Los Lagos, the region specific baseline has been elevated slightly above the epidemic threshold for the past four weeks. Of note, 6% of sentinel respiratory samples in Chile tested positive for a respiratory virus, of these 32% were positive for respiratory syncytial virus (RSV), and 27% were positive for influenza viruses (half of which were subtyped as pandemic H1N1 virus).

In Europe, overall influenza activity remained low with very low level co-circulation of pandemic and seasonal influenza type B viruses. The overall proportion of sentinel respiratory samples testing positive for influenza remained stable at about 5.3%; and the total number of sentinel influenza B virus detections continued to exceed that of influenza A viruses, primarily due to low level seasonal influenza type B virus circulation in the Russian Federation and Kazakhstan.

Source: http://www.who.int/csr/don/2010_05_07/en/index.html