Influenza

Influenza update

20 January 2012

Update number 151

Table of contents

- Summary
- Countries in the temperate zone of the northern hemisphere
- Countries in the tropical zone
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Countries in the temperate zone of the southern hemisphere
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From the peer-reviewed literature
- Virological surveillance

Summary

• 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.

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Countries in the temperate zone of the northern hemisphere

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

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. Three regions within two provinces (British Colombia and Saskatchewan) reported localized influenza activity and 18 regions within five provinces (British Colombia, Alberta, Ontario, Quebec and Saskatchewan) reported sporadic influenza activity. Fourteen influenza-associated hospitalizations were reported this week (six paediatric and eight adult). To date this season 30% of all paediatric hospitalisations have occurred in children under the age of two years, while 57% of all adult hospitalisations have occurred in patients aged >65 years. Of the 109 laboratory confirmed cases reported in the first week of January, 77% were influenza type A. Of the influenza A viruses that were subtyped, 88% were A(H3N2). Since August 2011 50% of all laboratory confirmed influenza A(H1N1)pdm09 cases, and 35% of all laboratory confirmed influenza B cases, have been in patients aged <5 years.

In the United States of America (USA), nationally, ILI consultations were low (1.7%) and remained below the baseline level (2.4%). The percentage of clinical specimens testing positive for influenza remained low at <3%; both ILI and positive test rates have continued to increase since mid-December. 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. Ninety-four percent of viruses detected in the first week of 2012 were influenza type A. Of the influenza A viruses subtyped, 92% were A(H3N2). Ninety-nine percent 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 eight were of the B/Victoria lineage and antigentically related to the northern hemisphere vaccine virus.

In Mexico, in contrast to Canada and the USA, 90% 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

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 has reported 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. Sixteen percent of the European sentinel samples tested for influenza in the first week of 2012 were positive, a continued increase from previous weeks. Influenza A(H3N2) was the most common virus identified in the first week of 2012. Ninety-two percent of influenza viruses detected since early October have been influenza type A; of those, 93% have been influenza A(H3N2). In the first week of 2012, all 130 subtyped influenza type A samples were of the H3N2 subtype.

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 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.

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Countries in the tropical zone

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, 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%, higher than in recent weeks and higher than at the same time last year. Other countries in tropical Asia continue to report small numbers of both A(H3N2) and influenza type B.

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Countries in the temperate zone of the southern hemisphere

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.

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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.

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