02 December 2011
Update number 148
- 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 influenza activity reported in Canada and some European countries.
• Significant influenza activity was reported in only a few countries of the tropical zone including Nicaragua, Costa Rica, and Brazil in the Americas, Cameroon in central Africa, and Cambodia and Lao People's Democratic Republic in South East Asia.
• Transmission in the temperate countries of the southern hemisphere has returned to inter seasonal levels, with some persistence of influenza A(H3N2) in Australia.
• In the United States of America limited human-to-human transmission of a novel influenza A(H3N2) virus was detected with no further reported spread to date. See literature review.
The influenza season has not yet begun in the northern hemisphere temperate zone, though some sporadic influenza activity has been reported in Canada. The majority of the countries in this zone reported low or no influenza activity in recent weeks. Influenza activity in Europe remains low overall; the Czech Republic, France, Ireland, Norway, the Russian Federation, Spain and Sweden have reported sporadic influenza activity.
Tropical countries of the Americas
Influenza activity in the tropical countries of the Americas is generally low or decreasing with the exception of Costa Rica where influenza A(H3N2) activity is increasing. In Nicaragua, transmission of the influenza A(H1N1)pmd09 virus that increased late September has been decreasing for the third consecutive week since its peak in week 42. Much lower numbers of influenza A(H3N2) have also been detected in the country. Low-level transmission of influenza A(H3N2) continues in El Salvador and Honduras after peaking in September. In the tropical area of Brazil an outbreak with influenza A(H1N1)pdm09 was reported in the city of Pedra Branca, Ceará.
In sub-saharan Africa, influenza transmission continues at low levels with 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 A(H3N2) detections. Sierra Leone has reported low level transmission of influenza A(H3N2), and Senegal has reported low level transmission of influenza type B after peaking in early November.
Influenza transmission in tropical Asia is active in localized areas. The high level transmission of a mixture of influenza A(H1N1)pdm09 and influenza type B in Cambodia and influenza A(H1N1)pdm09 in Lao People's Democratic Republic reported in the end of October continues, but seems to be decreasing. Viet Nam has continued to report sustained transmission of mainly influenza A(H1N1)pdm09 for most of the year, which seems now to be declining. Other countries of southern Asia continue to report small numbers of both influenza A(H3N2) and influenza type B.
In the temperate regions of South America influenza transmission has declined to inter- seasonal levels and the season appears to be largely over. Low or no influenza transmission is reported in all countrie
South Africa experienced a second peak of influenza transmission this season between late August and late October of influenza type B and A(H3N2), which followed an earlier peak of influenza A(H1N1)pdm09 in June. Transmission of all influenza viruses has declined to 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 detection of influenza type B, influenza type A (unsubtyped) and A(H3N2).
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.