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Influenza Update N? 209, 22 April 2014 (WHO, edited)

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  • Influenza Update N? 209, 22 April 2014 (WHO, edited)

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

    Influenza Update N? 209, 22 April 2014

    • Globally, the northern hemisphere influenza season appeared to be approaching interseasonal levels in most countries. As influenza detections declined, the proportion of influenza B detections increased slightly in many regions, especially Asia, the Middle East, and North America.
    • In North America, influenza levels continued to decline. Late season circulation of influenza B continued; however, the overall numbers of influenza detections remained low.
    • In Europe, influenza activity continued to decrease, as the region appeared to be coming to an end of the influenza season. A rise in the percentage of influenza specimens testing positive was observed, but the overall number of specimens declined. Influenza A(H3N2) and A(H1N1)pdm09 co-circulated, with low numbers of influenza B virus detected. In eastern Europe, influenza activity was higher later in the season compared to the north and the south-west, but detections have begun to decline as well.
    • In Eastern Asia, influenza activity approached interseasonal levels, and influenza B comprised the majority of influenza detections.
    • In Tropical Asia, influenza activity continued to decline.
    • In Northern Africa and Western Asia, influenza activity remained low in most countries, with influenza B the predominant virus detected.
    • In the Southern Hemisphere, influenza activity remained low and detections were sporadic.

    Based on FluNet reporting (as of 15 April 2014, 10:15 UTC), during weeks 13 to 14 (23 March 2014 to 5 April 2014), National Influenza Centres (NICs) and other national influenza laboratories from 82 countries, areas or territories reported data.

    The WHO GISRS laboratories tested more than 44 319 specimens.
    6717 were positive for influenza viruses, of which 4163 (62%) were typed as influenza A and 2554 (38%) as influenza B.

    Of the sub-typed influenza A viruses, 1149 (47.2%) were influenza A(H1N1)pdm09 and 1287 (52.8%) were influenza A(H3N2).

    Of the characterized B viruses, 224 (83%) belong to the B-Yamagata lineage and 46 (17%) 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 declined slightly from the previous week, continuing a decreasing trend after having peaked in January. Influenza B comprised the majority of detections, which is a shift from earlier in the season when A(H1N1)pdm09 was detected most frequently. However, overall activity declined and influenza A(H1N1)pdm09 remained the most commonly detected virus for the 2013-2014 season.

    In Canada, overall influenza activity decreased slightly, but influenza B levels remained elevated. Influenza B virus comprised the majority of detections in the previous weeks, and slighty more influenza B was observed to date this season compared to the same time during the 2012-13 season. However, influenza activity levels remained within the expected range for this time of year, and A(H1N1)pdm09 remained the predominant virus of the season.

    In the United States of America (USA), influenza activity continued to decrease slightly in most regions. Similar to Canada, the USA has seen an increased proportion of influenza B detections in recent weeks. The proportion of deaths attributed to pneumonia and influenza was below the epidemic threshold and the proportion of outpatient visits for ILI was 1.6% which is below the national baseline of 2.0%.

    In Mexico, influenza activity continued to decrease, and pneumonia rates were within expected levels for this time of year. In recent weeks, the percentage of influenza B in specimens testing positive for influenza increased from 24% to 38%. This trend was similar to other countries in the region, and overall detections remained low. Indicators in Mexico suggested the influenza season is near cessation.



    In Europe, overall activity declined. A rise in the percentage of influenza specimens testing positive was observed, but the overall numer of specimens declined. The majority of countries reported stable or decreasing trends and low intensity influenza activity. Influenza A(H1N1)pdm09 and A(H3N2) viruses circulated throughout the region with variability in predominance or codominance among countries, with very little circulation of influenza B virus.

    In eastern Europe, activity was elevated later in the season compared to other areas of Europe, but has begun to decline. This may be due to the earlier start of the season in the south-west and later start in the east.

    Eastern Europe detected both influenza A subtypes as well as influenza B viruses, with the majority being A(H3N2). In the north and south-west regions of Europe, detections continued to decline and activity was generally low. Overall, 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 continued to decrease.


    Northern Africa and the Western and Central Asia region

    In Central and Western Asia, influenza activity remained low in most countries.

    The Islamic Republic of Iran and Turkey reported low levels of influenza, with the majority of detections being influenza B virus. Israel and Pakistan reported decreased influenza detections, but overall influenza activity remained slightly elevated in these countries.

    Eastern Asia

    In the Eastern Asian region, 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 current predominant virus.

    In China, influenza activity continued to decline and activity approached interseasonal levels. Influenza B was predominant in both north and south China, with low detections of A(H3N2) and A(H1N1)pdm09 occurring as well. Despite recent increases in influenza B, influenza A remains the predominant virus during the season in China.

    In Mongolia, ILI activity continued to decrease, and was almost below the country?s upper tolerance limit of 60% for the first time in several weeks. The percentage of influenza positive specimens and hospitalized pneumonia patients also continued to decline. Influenza B was the predominant virus detected in early April, overtaking A(H3N2) and A(H1N1)pdm09 which had been circulating at higher levels earlier in the season. This pattern was aligned with trends seen in other areas of the region.

    Japan reported low levels of influenza activity, and levels declined from the previous week.

    Similar to other countries in the region, activity declined in the Republic of Korea, and influenza B comprised the majority of detections. ILI activity in Korea continued a decreasing trend but remained slightly above the national baseline level of 12.1%.

    Countries in the tropical zone

    Tropical countries of the Americas/Central America and the Caribbean

    The overall influenza activity in Central America and tropical areas of South America was at low levels. In some countries in the Caribbean, influenza activity had been slightly elevated in previous weeks, but limited new information is available.

    Central African tropical region

    In the African region, influenza activity was generally low. Influenza B circulated in low levels in West Africa.

    Tropical Asia

    In most South-East Asian countries, activity declined or remained low.

    Activity declined in Indonesia, Lao People?s Democratic Republic, and Thailand. In Thailand, influenza A(H1N1) and influenza B co-circulated, and in Indonesia influenza A(H3N2) and influenza B co-circulated.

    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