06 January 2012
Update number 150
- 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 below seasonal threshold levels, though notable increases in activity have been reported in some areas of Canada, Europe (Spain and Turkey), northern Africa (Tunisia and Algeria), and the middle East (Iran). The persistence of the increased activity over the last few weeks in these areas likely represents the start of the influenza transmission season.
• The viruses detected throughout the northern hemisphere temperate zone have been predominantly of the A(H3N2) subtype. Only very small numbers of influenza A(H1N1)pdm09 have been reported in recent weeks.
• Countries in the tropical zone reported low levels of influenza activity except for Costa Rica, which is primarily detecting influenza A(H3N2).
• Influenza activity in the temperate countries of the southern hemisphere is at inter-seasonal levels though Chile and Australia both report persistent transmission of A(H3N2) with smaller numbers of influenza type B in Australia.
Influenza activity in the northern hemisphere temperate regions is still below baseline, though increased respiratory disease activity and influenza virus detections have been noted in some areas.
In Canada, the percent of positive influenza tests and consultation rates for influenza-like illness (ILI) have persistently increased since mid-December. However, nationally influenza activity remained at inter-seasonal levels. Localized influenza activity was reported in the region of British Columbia and sporadic cases reported in nine regions of four provinces (Alberta, British Columbia, Ontario and Quebec). Three influenza outbreaks in a long term care facilities and two paediatric influenza hospitalisations were reported in the last week. Of the 63 laboratory confirmed cases reported, 51 were of the influenza A(H3N2), seven were unsubtyped influenza A, and two were influenza type B. To date, this season, there have been ten adult influenza hospitalisations of which six were over 65 years of age.
In the United States of America, nationally, ILI consultations were low (1.2%) and remained below the baseline level (2.4%) and the percentage of samples positive for influenza remained below 2%; both have increased since mid-December. Of the nearly 1000 virus detections reported since October 2011, 85% have been influenza type A. Of the influenza A viruses that have been subtyped, 84% were A(H3N2) and the remainder A(H1N1)pdm09. The proportion of deaths due to pneumonia and influenza reported in the 122 cities sentinel surveillance system was low compared to previous years.
In Europe, influenza activity remains low though respiratory disease activity and influenza virus detections have started to increase in some areas over a period of several weeks. ILI consultations and admissions for severe acute respiratory infections (SARI) remain at inter-seasonal levels overall. Of the 35 countries reporting on the geographical distribution of influenza activity, 21 reported no activity, 1 reported local activity (Italy) and 13 reported sporadic activity in recent weeks. Spain and Turkey reported notable increases in influenza virus detections among sentinel samples with percentages of positive samples of 17% and 23% respectively. Influenza A(H3N2) was the most common virus detected. In France the consultation rate for acute respiratory infections exceeded the seasonal baseline level; however, there was no corresponding increase in ILI consultations or influenza virus detections. Twenty-three percent of European sentinel samples tested for influenza in epidemiological week 51 were positive, a doubling from the previous week. Influenza A(H3N2) was the most common virus identified; 94% of 414 influenza A viruses characterized were the A(H3N2) subtype. All cause mortality reported in the European Mortality Bulletin is within the range normally expected at this time of season for all of the countries reporting to the system.
Northern Africa and Eastern Mediterranean
The northern Africa and eastern Mediterranean regions have been reporting increasing numbers of positive influenza specimens since October, particularly in Algeria, Tunisia and Iran. As in Europe, influenza A(H3N2) was the predominant subtype detected.
Temperate countries of Asia
In northern China, influenza activity increased slightly, to 8.6%, since the previous week; influenza B virus is still the predominant strain in China. Republic of Korea and Japan have both reported small but slightly increased numbers of influenza positive specimens in recent weeks, most of which were A(H3N2).
Tropical countries of the Americas
No notable influenza transmission has been reported in the majority of Caribbean and central American countries 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 or low level transmission were reported. Transmission of influenza A(H3N2) in Cameroon appears to be decreasing after peaking in mid-December 2011. Kenya has reported continuous influenza transmission; however, the number of positive specimens has been decreasing in the past 4 weeks and is now at a very low level.
Overall, the influenza activity in tropical Asia remained low. Since September, India has continued to report low level influenza B circulation. Following peaks in influenza activity in September, Lao People's Democratic Republic, Cambodia and Viet Nam have reported decreasing transmission which have now returned to low levels. Other countries in tropical Asia continue to report small numbers of both A(H3N2) and influenza type B.
In temperate countries of the southern hemisphere, influenza activity is at inter-seasonal levels; however, Chile and Australia both report low levels of persistent influenza A(H3N2), with much smaller numbers of influenza type B also reported in Australia.
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.