16 December 2011
Update number 149
- Countries in the temperate zone of the northern hemisphere
- Countries in the tropical zone
- Countries in the temperate zone of the southern hemisphere
- From the peer-reviewed literature
- Virological surveillance
• Influenza activity in the temperate regions of the northern hemisphere remains at low levels, with sporadic activity reported in Canada, the United States of America, and some European countries.
• Countries in the tropical zone mostly reported low influenza activity except Costa Rica, primarily influenza A(H3N2), and Cameroon, which is experiencing transmission of A(H3N2) following on recent peaks of A(H1N2)pdm09 and type B.
• Influenza activity in the temperate countries of the southern hemisphere is at inter-seasonal levels.
Please note the next update will be published on 6 January 2012
Sporadic reports of influenza activity have been reported in the temperate areas of northern hemisphere, though no country has yet crossed it's seasonal threshold. Canada reported localized influenza activity in eight regions, three outbreaks of influenza or influenza-like illness (ILI), and three influenza-related hospitalizations. In the United States, nationally, ILI consultations remained below the baseline and the percentage of samples positive for influenza was <2%, with sporadic detections of influenza A(H3N2) and influenza type B. In Europe, consultation rates for ILI continue to be low but nine countries have reported increasing trends. Only 1.8% of sentinel laboratory specimens tested were positive for influenza; A(H3N2) was the most common virus identified. Influenza activity in north China increased slightly as compared to the previous week with influenza type B as the predominant type.
Tropical countries of the Americas
No notable influenza transmission has been reported in the majority of the Caribbean and Central America with the exception of Costa Rica, which has continued to report increasing numbers of influenza A(H3N2) detections.
In sub-Saharan Africa, only sporadic detections of influenza viruses were reported with the exception of Cameroon. Influenza type B transmission began in June in Cameroon and appears to be declining overall since peaking in early September. Transmission of influenza A(H1N1)pdm09, which began about six weeks after influenza type B, appears to have peaked in early November, coincident with a rise in influenza A(H3N2) detections, which appears to be peaking only now. Sierra Leone, which has recently begun influenza surveillance, experienced a peak of A(H3N2) transmission in late August, which has now subsided. Kenya has reported continuous detections of influenza viruses throughout the year, which is now predominantly A(H3N2) with smaller numbers of A(H1N1)pdm09 and influenza type B.
The overall influenza activity in the tropical Asia remained low with some notable localized areas of transmission. India has reported influenza type B circulation since September. In Lao People's Democratic Republic, 11 of the 88 samples were tested positive for influenza A(H3N2) during 20-26 November. Transmission of the previously reported A(H3N2) in Thailand has now returned to very low levels of virus detection. Other countries of southern Asia continue to report small numbers of both A(H3N2) and influenza type B.
In the temperate regions of South America influenza activity has declined to inter- seasonal levels. Paraguay and Chile reported low numbers of influenza A(H3N2).
Influenza detections in this region are at very low levels.
Australia, New Zealand and South Pacific
In Australia and New Zealand, influenza activity is now at inter-seasonal levels. As was seen in the last year, inter-seasonal low level activity persists in Australia with low detections of influenza type B and A(H3N2). In the Pacific Islands, there was sustained levels of activity in American Samoa, Fiji, Marshall Islands and Northern Mariana Islands.
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 and Response System) 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.