Influenza update - 17 June 2011
Update number 136
• The influenza season has finished in the temperate countries of the northern hemisphere with only sporadic influenza virus detections occurring.
• Transmission in tropical areas remains low with localized circulation noted in the western and eastern regions of sub-Saharan Africa and low level circulation in some countries of northern South America.
• South Africa has reported a sharp increase in Influenza-Like Illness (ILI) and Severe Acute Respiratory Infection (SARI) rates, primarily influenza A(H1N1)2009.
• Influenza activity remains low in other temperate countries of the southern hemisphere.
The influenza season has ended in the northern hemisphere. Although sporadic detections of influenza viruses have been reported in many countries across the northern temperate zone, no active community transmission has been noted. Consultation rates for influenza-like illness (ILI) and severe acute respiratory infection (SARI) are at low levels and continue to decline in both the European and North American regions. In North Africa influenza circulation remains low although Egypt has reported five recent infections of the avian influenza A(H5N1) virus with three deaths since May.
Influenza activity in tropical areas remains low with localized transmission reported in some regions. Very low influenza activity was reported across central and tropical South America. Low level circulation of influenza type B and influenza A(H3N2) has been noted in Brazil. Colombia and the Plurinational State of Bolivia have reported a slight increase in influenza virus detection with low level circulation of influenza A(H1N1)2009 in Colombia and A(H3N2) in the Plurinational State of Bolivia. Colombia has also reported an increased proportion of intensive care unit admission of SARI cases of which children under the age of five contributed the highest proportion. Notably, respiratory syncytial virus has been widely circulating in Colombia in recent weeks.
Localized transmission has been noted across four countries in West Africa with Ghana and Togo reporting the largest numbers of laboratory-confirmed cases. In Ghana, the majority of the reported cases were influenza A(H1N1)2009 with a smaller proportion of influenza type B and even lower proportion of influenza A(H3N2). Togo has reported transmission primarily with influenza type B. Two other West African countries, Nigeria and Cameroon, both reported detection of influenza type B in modest numbers. In East Africa, Kenya has reported co-circulation of A(H1N1)2009 and influenza type B while Rwanda has reported transmission of A(H3N2).
Tropical Asian regions have also reported low influenza activity. Thailand, the Lao People's Democratic Republic and the Philippines have not detected any influenza virus since the last update. Influenza type B is the most common virus detected in the southern region of China, India and Cambodia, though in very low numbers, while influenza A(H1N1)2009 is more common in Viet Nam with 10% of ILI cases testing positive.
South American countries in the temperate region reported low numbers of influenza viruses with ILI consultation rates similar to those reported in the previous few weeks. Sporadic detection of influenza A(H1N1)2009 virus has been reported in Uruguay and Chile.
A sharp increase in ILI consultation rate has been noted by The National Institute for Communicable Diseases in South Africa. Influenza A(H1N1)2009 virus was the most common virus detected in the ILI cases. The numbers of SARI cases admitted to hospital have also increased and are also associated primarily with influenza A(H1N1)2009. Influenza surveillance from Madagascar had a modest increase in detections of influenza viruses. The proportion of influenza A(H3N2) has decreased there while the proportion of influenza type B seems to remain stable.
Australia and New Zealand and South Pacific
The influenza season does not appear to have started in either Australia or New Zealand. Australia reported stable ILI consultation rates below levels in 2008 and 2010 during the same period. The New South Wales Department of Health has also indicated that the rate of death associated with influenza and pneumonia remains below the seasonal threshold for this period. New Zealand reported the national ILI consultation rate below baseline activity. However, regional differences are noted where the baseline level is exceeded by one District Health Board from Northland. Influenza type B is the most common virus detected recently in New Zealand, though the numbers are quite small.
Source of data
The Global Influenza Programme monitors influenza activity worldwide and publishes an update every two weeks.
The updates are based on available epidemiological and virological data sources, including FluNet (reported by the Global Influenza Surveillance Network) and influenza reports from WHO Regional Offices and Member States. Completeness can vary among updates due to availability and quality of data available at the time when the update is developed.