[Source: World Health Organization, full PDF document: (LINK). Edited.]
Influenza Update N° 174 - 07 Dec. 12 2012
- Many countries of the northern hemisphere temperate region, especially in North America, reported increasing influenza virus detections. Canada and the United States of America (USA) crossed their seasonal threshold but activity was highest in the southern part of the USA. Influenza activity remained low in Europe but has continued to increase slightly.
- Low levels of influenza activity was reported in countries in southern and southeast Asia, except Cambodia.
- In Sub-Saharan Africa, influenza activity remains at low levels.
- Influenza activity in the temperate countries of the southern hemisphere continued at inter-seasonal levels.
Note: Global epidemiology and surveillance updates are periodically collected from data reported by National authorities or organizations responsible for reporting this data. For further information on specific influenza virus activity in the world and scientific literature for practitioners and other professionals in the field, please visit the links provided at the end of this document.
Countries in the temperate zone of the northern hemisphere
Countries of the temperate regions of the northern hemisphere reported continued increases in the detection of influenza viruses with an increase in rates of influenza-like illness (ILI) and percent of influenza positivity of specimens tested. Both the United States of America (USA) and Canada have announced the beginning of their influenza seasons.
Several of the southern states of the USA and southern provinces in Canada have reported an increase in influenza activity.
The USA has now reached the national seasonal threshold for the rate of influenza-like illness (ILI) activity. There have been differences noted between countries and the main influenza virus strains circulating. In Canada, there has been little influenza B activity, with much more reported in the USA, whilst in Mexico, influenza B is the predominant virus circulating.
In Canada, increases in all influenza indicators were reported since the last update. Nationally, the proportion of outpatient visits that were due to ILI increased since the previous week from 2.1% to 2.9% and the percentage of clinical specimens that tested positive for influenza virus from 5.9% to 9.6%. Seven regions have reported localized activity and 21 regions have reported sporadic activity. Eight influenza outbreaks have been reported, one in a hospital, five in long term care facilities and two in other settings. In the current reporting week, seven paediatric influenza-associated hospitalizations and 27 cases in adults ≥20 years of age were reported from the limited hospital surveillance system.
In Canada, 98% (271/278) of viruses detected were influenza A and 2% were influenza B. Of the influenza A viruses subtyped, 95% were A(H3N2) and 5% were A(H1N1)pdm09. Since the start of the season, the National Microbiology Laboratory (NML) has antigenically characterized 35 influenza viruses: all 22 influenza A(H3N2) influenza viruses were similar to the vaccine virus A/Victoria/361/2011 and all 4 A(H1N1)pdm09 viruses were similar to the vaccine virus A/California/7/2009. Of the influenza B viruses, 7 were similar to the vaccine virus B/Wisconsin/1/2010 (Yamagata lineage) and 2 were similar to B/Brisbane/60/2008 (Victoria lineage; a component of the 2011-2012 seasonal influenza vaccines). None of the 19 A(H3N2), 4 A(H1N1)pdm09 or 8 influenza B viruses tested so far this year were resistant to neuraminidase inhibitors.
Nationally, the USA have now marked the start of their influenza season, 6-7 weeks earlier than in recent previous years. ILI consultation rates have reached the seasonal threshold of 2.2% and 15.2% of the 5342 clinical specimens tested were positive for influenza virus, an increase from 7.5% in the last reporting week. The geographic extent of influenza activity was not uniform across the country, with five states in the south (Texas, Louisiana, Mississippi, Alabama, and Tennessee) experiencing high ILI activity and 39 states reporting minimal ILI activity.
In the USA, 70% of influenza viruses detected were influenza A and 30% influenza type B. Of the influenza A viruses with subtype information, 99.5% were influenza A(H3N2). Since October 2012, the Centre for Disease Control and Prevention in the United States of America has antigenically characterized 140 influenza viruses. All 90 A(H3N2) influenza viruses were A/Victoria/361/2011-like, the virus contained in the current trivalent seasonal vaccines. Both of the two influenza A(H1N1)pdm09 viruses tested were characterized as A/California/7/2009-like, the influenza A(H1N1) component of the current vaccines. Of the 48 influenza B viruses characterized, 34 were B/Wisconsin/1/2010-like (B/Yamagata lineage) and 14 were from the B/Victoria lineage. None of the 122 influenza A(H3N2), 2 A(H1N1)pdm09 or 81 influenza B viruses tested so far this year were resistant to neuraminidase inhibitors.
One infection with an influenza A(H3N2) variant virus (A(H3N2)v) was reported to CDC during week 47 from Iowa. No further cases have been identified in contacts of the case patient. This is the first A(H3N2)v infection reported since September 28, 2012. More information about H3N2v infections can be found at http://www.cdc.gov/flu/swineflu/h3n2v-outbreak.htm.
Levels of influenza activity throughout Europe remain low but some countries have reported increasing detections of influenza virus. In the last week of November, all 28 countries of the European Union/European Economic Area (EU/EEA) reported low-intensity activity of influenza-like illness or acute respiratory infection. For the whole of Europe, 3% of clinical specimens were positive for influenza virus in the third week of November. In the fourth week of November, the percentage positive had increased to nearly 9% (EU/EEA data only). In addition, an observation of increasing ILI/ARI activity has been reported by some countries including Poland, Slovakia, Hungary, Serbia, Lithuania, Estonia, Belarus, Ukraine, Moldova, Armenia, Uzbekistan and central Russia.
Of the influenza virus detections in sentinel specimens since week 40/2012, 46% were type A and 54% were type B viruses.
Of the A viruses subtyped, two thirds were A(H3N2) and one third were A(H1N1).
Since week 40, two countries (United Kingdom and Germany) have antigenically characterized 13 influenza viruses. Six influenza A/Victoria/361/2011 (H3N2)-like, two A/Perth/16/2009 (H3N2)-like, three B/Florida/4/2006-like and two B/Wisconsin/1/2010-like.
None of the 15 specimens tested, including A(H3N2), A(H1N1)pdm09 and B viruses, were resistant to neuraminidase inhibitors, oseltamivir and zanamavir.
Northern Africa and the eastern Mediterranean Region
Influenza activity has been noted in the eastern Mediterranean region at low levels.
Algeria has reported some transmission of influenza A(H3N2) and influenza B viruses.
Bahrain has continued to report influenza A(H1N1)pdm09 detections in recent weeks. After previous influenza A(H1N1)pdm09 virus detections, Israel is now reporting mainly influenza A (H3N2) at low levels.
ILI activity remained at low levels throughout the temperate Asian region.
In northern China, there were 44 samples positive for influenza (5.5%): 34 influenza A (30 A(H3N2)), 10 influenza B (lineage undetermined). This represents an increase from the previous week, where 3.3% of samples were influenza positive.
In Mongolia, influenza activity is low with 3 out of 82 samples (2.5%) positive for influenza (all A(H3N2)). Low activity of influenza remained also in both Republic of Korea and Japan.
Countries in the tropical zone
Tropical countries of the Americas
In Central America, declining influenza B and influenza A(H3N2) activity has been noted in Nicaragua. Influenza A(H3N2) is being reported in Honduras but activity has yet to peak. RSV activity continues to be noted in the area with Costa Rica, Panama and Honduras reporting cases.
In the Caribbean, Jamaica is reporting influenza B activity at low levels and in Cuba, following previous influenza B detections, influenza A(H1N1)pdm09 has now been reported. In Guadalupe and Martinique, the epidemic of respiratory syncytial virus has now declined.
In the tropical zone of South America, influenza activity continued to decline with low numbers of virus detections being reported. In Brazil and Paraguay, the overall trend of influenza was decreasing with sporadic detection of influenza A(H3N2) and B viruses reported. Peru has noted both influenza A(H1N1)pdm09 and influenza B transmission in the past few months, but is generally at low levels.
Influenza remains to circulate in parts of sub-Saharan Africa, although most countries that have reported a decrease, including Côte d’Ivoire , Cameroon, Ethiopia and Ghana, reported influenza A(H1N1)pdm09 exclusively, while A(H3N2) and influenza B was circulating in Cameroon and Kenya. Madagascar reported continued circulation of influenza B.
Influenza continued to circulate in tropical Asia, but appeared to be decreasing overall. India and Lao PDR, reported primarily influenza A(H1N1)pdm09, with declining influenza positive samples from its peak in late-September. Sri Lanka and Thailand reported circulation of all three influenza sub-types, although the number of positive samples was also decreasing. In Cambodia, the number of influenza positive samples remained similar to previous weeks, with influenza A(H3N2) co-circulating with influenza B, while in Viet Nam, influenza B is predominant, but decreasing.
Influenza activity in Singapore and southern China, including Hong Kong SAR, remained below seasonal thresholds.
Countries in the temperate zone of the southern hemisphere
Influenza activity has continued to decline in all temperate countries of the southern hemisphere and is now at inter-seasonal levels.
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.
Link to web pages
- Epidemiological Influenza updates: http://www.who.int/influenza/surveillance_monitoring/updates/latest_update_GIP_surveillance
- Epidemiological Influenza updates archives 2012: http://www.who.int/influenza/surveillance_monitoring/updates/GIP_surveillance_2012_archives
- Virological surveillance updates : http://www.who.int/influenza/gisrs_laboratory/updates/summaryreport
- Virological surveillance updates archives : http://www.who.int/influenza/gisrs_laboratory/updates/en/index.html