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Influenza Update N? 208, 7 April 2014 (WHO, edited)

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  • Influenza Update N? 208, 7 April 2014 (WHO, edited)

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

    Influenza Update N? 208, 7 April 2014

    • Globally, the northern hemisphere influenza season appeared to be approaching interseasonal levels in most countries. The proportion of influenza B detections however increased slightly in many regions, especially Asia, the Middle East, and North America.
    • In North America, influenza levels continued to decline and the season was coming to its end. Late season circulation of influenza B continued, however, the overall levels of influenza remained low.
    • In Europe, influenza activity declined, and influenza intensity was reported as low by most countries. Similar to North America, Europe appears to be coming to an end of the influenza season. Some increases in the proportion of A(H3N2) detections were seen in comparison to A(H1N1)pdm09, but overall levels decreased.
    • In Eastern Asia, influenza activity was approaching interseasonal levels, with influenza B emerging as the current predominant virus. This timing aligns with previous seasonal influenza trends in the region. Mongolia continues to experience elevated influenza activity, despite levels beginning to decline.
    • In Tropical Asia, influenza activity continued to decline, aligning with global seasonal trends. While in Thailand influenza activity remained elevated, small decreases were seen.
    • In Northern Africa and Western Asia, influenza activity remained low despite the increasing proportion of influenza B positive samples.
    • In the Caribbean, influenza activity remained low and at interseasonal levels in most countries, however ILI activity and influenza detections increased in Guyana and Guadeloupe.
    • In the Southern Hemisphere, influenza activity remained low and detections were sporadic.
    • Based on FluNet reporting (as of 3 April 2014, 12:35 UTC), during weeks 11 to 12 (9 March 2014 to 22 March 2014), National Influenza Centres (NICs) and other national influenza laboratories from 96 countries, areas or territories reported data.
      • The WHO GISRS laboratories tested more than 65 498 specimens.
      • 10 986 were positive for influenza viruses, of which 7407 (67.4%) were typed as influenza A and 3579 (32.6%) as influenza B.
      • Of the sub-typed influenza A viruses, 2747 (57%) were influenza A(H1N1)pdm09 and 2072 (43%) were influenza A(H3N2).
      • Of the characterized B viruses, 222 (87.1%) belong to the B-Yamagata lineage and 33 (12.9%) to the B-Victoria lineage.

    For updates on human infections with avian influenza A(H7N9) virus see the WHO website


    Countries in the temperate zone of the northern hemisphere

    North America

    In North America, overall influenza activity continued to decrease, with indicators showing the influenza season was coming to a close in the region. Some late season circulation of influenza B continued, mainly in Canada. But iInfluenza A(H1N1)pdm09 remained the predominant virus in the region for the season.

    Canada experienced a slight decrease in overall influenza activity. Current influenza activity is at an expected level for this time of year. Influenza B remained the predominant strain currently in circulation, comprising 75% of influenza detections. However, A(H1N1)pdm09 remained the most common virus detected in the season overall. Influenza B virus affected significantly greater proportions of people in the age groups >65 and 5-19 in comparison to the A(H1N1)pdm09 virus.

    In the United States of America (USA), influenza activity continued to decrease slightly, with indicators suggesting the season was ending. The proportion of deaths attributed to pneumonia and influenza was below the epidemic threshold. The proportion of outpatient visits for ILI was 1.6% which is below the national baseline of 2.0%. Influenza A(H1N1)pdm09 continued to be the predominant virus affecting the USA during this season.

    In Mexico, influenza activity continued to decrease, with pneumonia rates within expected levels for this time of year. Of the positive influenza samples, 76% were influenza A (48% A(H1N1)pdm09, 44% A(H3N2), 8% not subtyped) and 24% were influenza B. The proportion of influenza B increased from 10% to 24% from early March to mid- March. Over 90% of the reported influenza associated deaths were associated with influenza A(H1N1)pdm09.



    In Europe, overall influenza activity declined.The majority of countries reported stable or decreasing trends and low intensity influenza activity.

    Clinical consultation rates for ILI and ARI returned to baseline levels in most countries, and the percentage of SARI patients who tested positive for influenza decreased for the third consecutive week.

    Very few countries reported increasing trends .

    Russia reported some increased influenza activity, mainly due to A(H3N2) virus.

    In Europe, compared to previous weeks, A(H3N2) virus increased in the proportion of influenza A detections reported with very little circulation of influenza B.


    Northern Africa and the Western and Central Asia region

    In Central and Western Asia, influenza activity remained low, in line with trends from previous years. Influenza activity declined in the Middle East, including the Islamic Republic of Iran, Pakistan, and Turkey, and influenza B has begun to replace A(H1N1)pdm09 as the most prevalent virus. Activity in Israel has been elevated in recent weeks with all three subtypes circulating, but detections began to slowly decline.

    Eastern Asia

    In Eastern Asia, influenza activity continued to decline. Influenza A(H1N1)pdm09, A(H3N2), and influenza B viruses co-circulated, with influenza B surpassing A(H1N1)pdm09 as the predominant virus.

    In China, the number of influenza positive specimens continued to decline. China approached interseasonal levels, which aligned with the trends from their previous seasons. Overall influenza activity in the Hong Kong Special Administrative Region of the People?s Republic of declined slowly since the beginning of March, however influenza B remained at a relatively high level.

    Mongolia experienced an elevated burden of ILI and pneumonia cases this influenza season compared to previous years. ILI activity in Mongolia continued to decrease significantly since mid-February, however the proportion of outpatient visits reporting ILI symptoms remained above the country?s upper tolerance limit of 60%. The percentage of influenza positive specimens and hospitalized pneumonia patients also declined.

    ILI activity continued to decrease in Japan, where a lower proportion of positive specimens and fewer ILI cases compared to early March were reported.

    Despite an increase in influenza B prevalence, overall ILI and influenza activity in the Republic of Korea declined further from their peak in February.


    Countries in the tropical zone

    Tropical countries of the Americas/Central America and the Caribbean

    Overall influenza activity in Central America and tropical areas of South America was at low levels. Some countries in the Caribbean reported a slight increase in virus detections which might signal the start of the influenza season.

    In Guyana, ILI activity began to increase and was above expected levels for this time of year. Influenza A(H1N1)pdm09, A(H3N2), and influenza B were all circulating. Among the other French territories, Guadeloupe also declared the start of their influenza season. The remainder of Caribbean countries countinued to report low activity at this time.

    Central African tropical region

    In the African region, influenza activity was generally low. Influenza B circulated in low levels in West Africa. Influenza activity in Mauritius decreased slightly but remained elevated, with the majority of detections being A(H1N1)pdm09.

    Tropical Asia

    South-East Asian countries generally experienced low levels of influenza, Viet Nam and Singapore reported decreased influenza activity. Thailand however continued to experience elevated influenza activity compared to recent weeks.

    Countries in the temperate zone of the southern hemisphere

    In the Southern Hemisphere ILI activity remained relatively low, with low level circulation of influenza A(H1N1)pdm09, A(H3N2)and influenza B.

    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 WHO 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