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Published Date: 2012-01-20 14:55:22
Subject: PRO/EDR> Influenza (03): WHO update
Archive Number: 20120120.1016834

INFLUENZA (03): WHO UPDATE
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International Society for Infectious Diseases
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Date: Fri 20 Jan 2012
Source: WHO Surveillance and monitoring [summ., & edited]
http://www.who.int/influenza/surveillance_monitoring/updates/latest_update_GIP_surveillance/en/index.html

WHO update number 151
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Summary
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- Influenza activity in the temperate regions of the northern hemisphere remains low overall though notable local increases in activity have been reported in some areas of Canada, Europe (Turkey, Spain, Italy, and Malta), northern Africa (Tunisia and Algeria), China, and the middle East (the Islamic Republic of Iran).
- Countries in the tropical zone reported generally low or undetectable levels of influenza activity with the exception of southern China, where influenza type B detections are increasing, and Costa Rica, which continues to report influenza A(H3N2) but at declining levels.
- Influenza activity in the temperate countries of the southern hemisphere is at inter-seasonal levels though Chile, Paraguay, and Australia all report persistent low level transmission of A(H3N2) during their summer season.
- The most commonly detected virus type or subtype throughout the northern hemisphere temperate zone has been influenza A(H3N2) with the exception of Mexico, where influenza A(H1N1)pdm09 is the predominant subtype circulating, and China which is reporting a predominance of influenza type B. Other than Mexico, only very small numbers of influenza A(H1N1)pdm09 have been reported globally.
- Reports from countries that do antigenic characterization indicate that nearly all influenza A viruses tested are antigenically related to those viruses included in the current trivalent influenza vaccine. While many of the influenza type B viruses are of the Yamagata lineage, which is not included in the current vaccine, overall numbers of influenza B virus detections are quite low compared to influenza type A (with the exception of China noted above).
- Oseltamivir resistance continues to be observed at very low levels and has not increased notably over levels reported in previous seasons.

Countries in the temperate zone of the northern hemisphere
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Though influenza activity in most countries of the northern hemisphere continues to be below national baselines, persistent upward trends have been reported across the temperate region and in some areas the season has now clearly started.

North America
North America circulation of influenza viruses (late March 2011-January 2012 (snapshot)
http://www.who.int/influenza/surveillance_monitoring/updates/2012_01_20_influenza_north_america_circulation_main.jpg

The national consultation rate for influenza-like illness (ILI) in Canada continued to increase compared to previous weeks though it remains within expected levels for this time of year. 3 regions within 2 provinces (British Colombia and Saskatchewan) reported localized influenza activity and 18 regions within 5 provinces (British Colombia, Alberta, Ontario, Quebec, and Saskatchewan) reported sporadic influenza activity. 14 influenza-associated hospitalizations were reported this week (6 paediatric and 8 adult). To date this season 30 per cent of all paediatric hospitalisations have occurred in children under the age of 2 years, while 57 per cent of all adult hospitalisations have occurred in patients older than 65 years. Of the 109 laboratory confirmed cases reported in the 1st week of January 2012, 77 per cent were influenza type A. Of the influenza A viruses that were subtyped, 88 per cent were A(H3N2). Since August 2011 50 per cent of all laboratory confirmed influenza A(H1N1)pdm09 cases, and 35 per cent of all laboratory confirmed influenza B cases, have been in patients younger than 5 years.

In the United States of America (USA), nationally, ILI consultations were low (1.7 per cent) and remained below the baseline level (2.4 per cent). The percentage of clinical specimens testing positive for influenza remained low at less than 3 per cent; both ILI and positive test rates have continued to increase since mid-December 2011. ILI activity was moderate in one State (Alabama), and low or minimal in the remaining states. Regional influenza activity was observed in one state (Colorado); local influenza activity was observed in 4 states (Texas, Virginia, New Hampshire, and Massachusetts), and the rest of the states continued to report sporadic or no influenza activity. The proportion of deaths due to pneumonia and influenza reported in the 122 cities sentinel surveillance system remains low compared to previous years. 94 per cent of viruses detected in the 1st week of 2012 were influenza type A. Of the influenza A viruses subtyped, 92 per cent were A(H3N2). 99 per cent of influenza A viruses characterized were antigenically related to viruses contained in the current seasonal trivalent influenza vaccine. Nine of the 17 influenza B viruses tested belong to the B/Yamagata lineage of viruses; the other 8 were of the B/Victoria lineage and antigenically related to the northern hemisphere vaccine virus.

In Mexico, in contrast to Canada and the USA, 90 per cent of all laboratory-confirmed cases of influenza since late December 2011 were influenza A(H1N1)pdm09. Localized outbreaks of A(H1N1)pdm09 have also been detected in parts of the country.

Europe
Western Europe circulation of influenza viruses (late March 2011-January 2012 (snapshot)
http://www.who.int/influenza/surveillance_monitoring/updates/2012_01_20_influenza_western_europe_circulation_main.jpg

In Europe, overall influenza activity remains low though respiratory disease activity and influenza virus detections have started to increase in some areas. The European Centre for Disease Prevention and Control (ECDC) has reported [see comment below] that the influenza season has begun on the continent and is currently dominated by vaccine type influenza A(H3N2), though ILI consultations and admissions for severe acute respiratory infections (SARI) remain at inter-seasonal levels overall. Of the 44 countries reporting on the geographical distribution of influenza activity, 16 reported no activity, 21 reported sporadic activity, 4 reported local activity and 3 (Turkey, Italy, and Malta) reported regional activity in recent weeks. Notable increasing trends in virus detections have been observed to be persisting over several weeks in Spain, Turkey, Sweden, Norway, and Italy; only Turkey is reporting cases numbers that are higher than at this time last season. Turkey and Malta reported medium intensity of influenza activity and moderate impact on their health care services. All-cause mortality remains low for this time of the season. 16 per cent of the European sentinel samples tested for influenza in the 1st week of 2012 were positive, a continued increase from previous weeks. Influenza A(H3N2) was the most common virus identified in the 1st week of 2012. 92 per cent of influenza viruses detected since early October 2011 have been influenza type A; of those, 93 per cent have been influenza A(H3N2). In the 1st week of 2012, all 130 subtyped influenza type A samples were of the H3N2 subtype.
[see below for the ECDC Weekly Surveillance Report for the period 9-15 Jan 2012]

Northern Africa and Eastern Mediterranean
The northern Africa and Eastern Mediterranean regions have been reporting increasing numbers of positive influenza specimens since October 2011, particularly in Algeria, Tunisia, and the Islamic Republic of Iran. Increased virus detection is widespread but not universal. As in Europe, influenza A(H3N2) was the predominant subtype detected, accounting for nearly all of the viruses that have been subtyped.

Temperate countries of Asia
In northern China, both the percentage of outpatient visits that were due to ILI and the proportion of specimens testing positive for influenza increased since the last report. In contrast to other reporting regions, influenza type B virus is the predominant type in China. The Republic of Korea and Japan have reported a persistent increase in numbers of influenza positive specimens in recent weeks, predominantly A(H3N2), and Japan also reported increasing rates of ILI.

Countries in the tropical zone
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Tropical countries of the Americas
No notable active influenza transmission has been reported in the majority of the Caribbean and Central American countries with the exception of Costa Rica, which has a decreasing trend of influenza A(H3N2) detections since transmission there peaked in late 2011.

Sub-Saharan Africa
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, although there has been a recent increase in the detection of influenza B. Kenya has reported continuous influenza transmission for the last year; however, the number of positive specimens has been decreasing in the past 4 weeks and is now at a very low level.

Tropical Asia
Overall, the influenza activity in tropical Asia remained low. Since September 2011, India has continued to report low level influenza B circulation. Southern China is reporting increasing numbers of influenza type B and the percentage of hospital visits for ILI has increased to 3.7 per cent, higher than in recent weeks and higher than at the same time last year [2011]. Other countries in tropical Asia continue to report small numbers of both A(H3N2) and influenza type B.

Countries in the temperate zone of the southern hemisphere
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Chile circulation of influenza viruses (snapshot)
http://www.who.int/influenza/surveillance_monitoring/updates/2012_01_20_influenza_chile_circulation_main.pdf

Australia circulation of influenza viruses (snapshot)
http://www.who.int/influenza/surveillance_monitoring/updates/2012_01_20_influenza_australia_circulation_main.pdf

In temperate countries of the southern hemisphere, influenza activity is at inter-seasonal levels; however, Chile, Paraguay, and Australia all report low levels persistent influenza A(H3N2). Similar out-of-season low level transmission was observed earlier in South Africa but has not persisted.

Source of data
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The Global Influenza Programme monitors influenza activity worldwide and publishes an update every 2 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.

Maps and graphs
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Global circulation of influenza viruses (snap shot)
http://www.who.int/influenza/surveillance_monitoring/updates/2012_01_06_influenza_global_circulation.pdf

Northern hemisphere circulation of influenza viruses (real time)
http://gamapserver.who.int/gareports/Default.aspx?ReportNo=5&Hemisphere=Northern

Southern hemisphere circulation of influenza viruses (real time)
http://gamapserver.who.int/gareports/Default.aspx?ReportNo=5&Hemisphere=Southern

Global Health Observatory -- Map Gallery
http://gamapserver.who.int/mapLibrary/app/searchResults.aspx

--
communicated by:
ProMED-mail rapporteur Marianne Hopp

[Interested readers are recommended to access the diagrams referenced to above to gain a rapid appreciation of the current influenza situation.

Other than Mexico, only very small numbers of influenza A(H1N1)pdm09 have been reported globally. Reports from countries that do antigenic characterization indicate that nearly all influenza A viruses tested are antigenically related to those viruses included in the current trivalent influenza vaccine.

The ECDC Report for week 2 2012 [9-15 Jan 2012] (http://ecdc.europa.eu/en/publications/Publications/120120_SUR_Weekly_Influenza_Surveillance_Overview.pdf) states that: low influenza activity was notified by 25 of the 27 countries reporting, (Italy and Spain reported medium activity) with 5 countries reporting local or regional spread. This week 10 countries reported increasing trends compared with 5 last week [2-8 Jan 2012]. Of 803 sentinel specimens collected and tested during week 2 2012, 137 (17.1 per cent) were positive for influenza viruses. This is higher than in week 1 and continues an upward progression since December 2011 (the high figure in week 52/2011 [26 Dec 2011-1 Jan 2012] was an artifact of the Christmas/New Year holiday). Of 908 influenza A viruses sub-typed from sentinel and non-sentinel sources since week 40/2011 [3-9 Oct 2011], 851 (93.7 per cent) were of the H3 subtype. Since week 40/2011, no antiviral resistance has been detected. Since week 40/2011, 195 severe acute respiratory infection (SARI) cases have been reported by 6 countries. 77 were confirmed influenza-positive cases and of those typed or sub-typed, 15 were A(H1N1)pdm09, 30 were A(H3) and 5 were influenza B viruses. Influenza transmission is progressing slowly in Europe this season and is currently dominated by A(H3N2) viruses. - Mod.CP]

See Also