[Source: World Health Organization, full PDF document: (LINK). Edited.]


Influenza Update N° 193, 30 August 2013


Summary
  • Influenza activity in the northern hemisphere temperate zones remained at inter-seasonal levels.
  • In most parts of tropical Asia influenza activity decreased.
  • In Central America and the Caribbean, influenza and Respiratory Syncytial Virus (RSV) transmission declined. RSV, influenza A(H1N1)pdm09 and influenza A(H3N2) were the main respiratory viruses reported.
  • In tropical South America, influenza A(H1N1)pmd09 virus predominated. A significant increase in influenza A(H1N1)pdm09 activity was observed in Peru in the middle of July, while influenza activity in general decreased in Venezuela, Ecuador and Brazil.
  • Influenza activity peaked in the temperate areas of South America and in South Africa in late June. Influenza activity in these areas was primarily associated with influenza A(H1N1)pdm09 virus throughout the season, with increasing influenza A(H3N2) virus detections observed towards the end.
  • In Australia and New Zealand, numbers of influenza viruses detected and rates of influenza-like illness were lower than in previous years, but showed an increasing trend. Influenza A(H3N2) and type B were much more commonly detected than A(H1N1)pdm09 in both countries.
  • As of 11 August, a total of 135 cases of influenza A(H7N9) virus infection were reported. For more details see: http://who.int/influenza/human_animal_interface/influenza_h7n9/en/index.html
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Countries in the temperate zone of the northern hemisphere

North America

Overall influenza activity in North America remained at low levels throughout the region. In Canada and the United States of America (USA), influenza activity remained at inter-seasonal levels.

The USA has reported 16 human infections with influenza A(H3N2)v virus in 2013 since the first case in June. For more details see http://www.cdc.gov/flu/swineflu/h3n2v-cases.htm.

Mexico continued to report some influenza activity. According to laboratory data from beginning of August, 175 samples were tested and 14.3% were positive for influenza. Among the positive influenza samples, 92.0% were influenza A,of which 43.5% were A(H1N1)pdm09 and 58.1% were A(H3N2), and 8.0% were influenza B.


Europe

Influenza activity in Europe remained at inter-seasonal levels. Consultation rates for ILI and ARI were at low levels for all countries in the region. None of the specimens collected from sentinel sites tested positive for influenza.


Northern Africa and the Western Asia region

Influenza activity was low in the Northern Africa and western Asia regions.


Northern Asia

Influenza activity in the temperate region of Asia remained at inter-seasonal levels since late May.

As of 11 August 2013, 135 cases of influenza A(H7N9) were identified, of which 44 died. There were no new cases since the last update. More and updated information is posted at: http://who.int/influenza/human_animal_interface/influenza_h7n9/en/index.html

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Countries in the tropical zone

Tropical countries of the Americas/Central America and the Caribbean

In the Caribbean and Central America the respiratory virus infections continued their decreasing trend. All samples testing positive for influenza were influenza type A. Co-circulation of influenza A(H1N1)pmd09 and influenza A(H3N2) continued in Cuba, Costa Rica, Dominican Republic and Nicaragua, whereas Guatamala reported mainly influenza A(H1N1)pmd09 virus detections.

Influenza transmission was still high in Costa Rica: in the last three weeks, over 30% of the analyzed samples were positive for influenza.
During the last weeks, RSV predominated in Cuba and Guatamala and adenovirus predominated in Honduras.

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In tropical South America, influenza activity decreased overall.

In Colombia, the proportions of outpatient visits, hospitalizations, and ARI-associated ICU admissions did not change significantly from the previous week. Of the samples analyzed, 10% was positive for influenza (mainly influenza A(H1N1)pdm09).

In Venezuela, after having peaked in early June, the ARI and pneumonia levels returned to their expected activity levels for this time of the year. The percentage positive samples for respiratory virus decreased in the last weeks to 0%.

A decrease in SARI hospitalizations was also seen in Ecuador. Of the 146 SARI samples analyzed in the last two weeks, 47% tested positive for influenza (of which 85% were influenza A(H1N1)pdm09).

A sharp increase in influenza A(H1N1)pdm09 transmission was however observed in Peru in the middle of July and transmission levels have continued to be high.

In Bolivia co-circulation of influenza A(H1N1)pdm09 and influenza B subtypes continued. Although the SARI hospitalizations decreased, still 22% (Santa Cruz) and 31% (La Paz) of the tested samples were positive for influenza.

In Brazil, the influenza virus detections in both ILI and SARI cases decreased.

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Central African tropical region

Cote d’Ivoire and Ghana reported circulating influenza virus.

Cote d’Ivoire reported predominantly A(H1N1)pdm09 and influenza B transmission, whereas in Ghana, there were more detections of influenza A(H3N2).

Cameroon and Kenya reported low influenza activity. After having peaked at the end of May, influenza activity in Madagascar continued to decrease and currently only influenza B has been detected.


Tropical Asia

Influenza transmission in southern Asia remained consistently low in all countries. Both influenza A(H3N2) and influenza A(H1N1)pdm09 viruses were reported in this area.

In the south of China and the Hong Kong, China Special Administrative Region (SAR), a change in circulating influenza subtype from A(H1N1)pdm09 (which predominated throughout the last season) to A(H3N2) was observed over the last weeks. In addition in the Hong Kong SAR, a slight increase in influenza associated hospital admissions was seen in the 0-4 and >65 years old patients.

In Southeast Asia, influenza activity has been decreasing with continued circulation of influenza A(H3N2) virus predominating in Thailand and influenza A(H1N1)pdm09 virus predominating in Cambodia.

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Countries in the temperate zone of the southern hemisphere

Temperate countries of South America

Influenza and RSV activity showed a decreasing trend and RSV continued to be the most commonly respiratory virus detected in temperate South America. Influenza virus transmission continued to decrease since peaking in June and was primarily associated with influenza A(H1N1)pdm09 with the exception of Paraguay, where influenza A(H3N2) was the predominant virus.

In Chile, the national ILI consultation rate and the proportion of SARI-associated hospitalizations continued to decline. RSV remained the most common respiratory virus detected. Among 1418 samples collected, only 4% were positive for influenza viruses (mainly influenza A(H1N1)pdm09).

In Argentina, the number of ILI and SARI cases peaked in week 26, but declined since then. This decline was also reflected in the samples positive for influenza viruses. Of the 1405 samples analyzed, only 5% were positive for influenza.

In Paraguay, influenza activity has been decreasing since week 27. Among the positive samples, influenza A(H3N2) and influenza B predominated.

In Uruguay influenza activity continued to decrease. Influenza A(H1N1)pdm09 and RSV were the predominant respiratory viruses detected.

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Temperate countries of Southern Africa

After a peak in influenza activity in South Africa due to influenza A(H1N1)pmd09 in June, a slight increase was observed in the last few weeks due to increased influenza A(H3N2) and influenza B circulation. This change of influenza subtype was seen in both ILI cases and SARI cases.

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Oceania, Melanesia and Polynesia

ILI activity in Australia, New Zealand and the Pacific Islands showed an increasing trend during the last few weeks and may be indicating the start of a late season.

Across jurisdictions of Australia the distribution of influenza types and subtypes was variable. In Victoria there was a predominance of influenza type B, whereas most other states reported a predominance of influenza type A, with New South Wales reporting mostly A(H1N1)pdm09 and Western Australia mostly A(H3N2) virus detections. Influenza positivity levels ranged from 11.0% in the national sentinel laboratory surveillance to 20.5% in the Australian Sentinel Practices Research Network (ASPREN) . Over the past few weeks there was a continued seasonal increase in influenza associated hospitalisations. Around 10% of influenza cases were admitted directly to ICU. The age distribution of hospital admissions showed peaks in the 0-9 and over 60 years age groups.

In New Zealand, influenza activity continued to remain below the baseline threshold, but with increasing trends. 136 out of 349 samples received were positive for influenza: 64 were influenza B, 51 were influenza A(H3N2), 9 were influenza A(H1N1)pdm09 and 12 influenza A (not subtyped). In Auckland and Counties Manukau District Health Boards, influenza activity increased slightly in community surveillance and decreased slightly in hospital surveillance.

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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.


Link to web pagesContact fluupdate@who.int


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