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27 May 2013

Influenza Update N° 186 - 24 May 2013 (WHO, May 27 2013, edited)

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

Influenza Update N° 186 - 24 May 2013



  • Influenza activity in the northern hemisphere temperate zones decreased to low levels with some continued transmission in some areas including Canada and Egypt.
  • In the tropical areas, influenza activity varied but was similar to previous weeks. Madagascar reported to be in an epidemic since the beginning of April.
  • Influenza activity in the southern hemisphere was low with a slight increase reported in South Africa.
  • For information on H7N9 please see WHO website at:
  • A summary review of influenza activity in the northern hemisphere influenza season will be published in the World Epidemiological Report on 31 May 2013.


Note: Global epidemiology and surveillance updates are periodically collected from data reported by National authorities or organizations responsible for reporting this data. For further information on specific influenza virus activity in the world and scientific literature for practitioners and other professionals in the field, please visit the links provided at the end of this document.



Countries in the temperate zone of the northern hemisphere

Influenza activity in the northern hemisphere temperate zones has decreased to low levels but with some continued transmission in some areas.

In Canada, where the influenza season has been prolonged due to the late season circulation of influenza type B, type B transmission continued at decreasing levels in early May. A number of influenza-associated hospitalizations were also reported, nearly all of them associated with influenza type B.

In the United States of America, Europe, and northern Asia transmission has returned to inter-seasonal levels.

In North Africa, some low grade persistence of influenza type B and influenza A(H1N1)pdm09 was reported in early May following a peak of transmission of both viruses in early April.

A summary review of the northern hemisphere 2012-13 influenza season will be published in the World Epidemiological Report on 31 May.



Countries in the tropical zone

Tropical countries of the Americas/Central America and the Caribbean

In the Central America and Caribbean regions and tropical South America, influenza activity has remained similar with mainly influenza A(H1N1)pdm09.

In Brazil influenza activity overall decreased, but the trend in SARI cases with mainly influenza A(H1N1)pdm09 increased, mainly in in the southern areas. Ecuador in contrast reported decreasing activity with influenza A(H3N2).



Central African tropical region

A few countries in the Central African tropical region have reported low grade, persistent influenza transmission with varying proportions of all three virus types over the past several weeks. Madagascar reported also an increasing level in influenza activity since the beginning of April with influenza A(H1N1)pdm09 as the most common virus.


Tropical Asia

Influenza transmission in southern Asia was similar to previous week with co-circulation of all three viruses. Transmission in India appears to have peaked in late March and was primarily associated with influenza A(H1N1)pdm09 with slightly smaller numbers of A(H3N2) and influenza B viruses.

In Sri Lanka, influenza activity has reached the highest level throughout this season with influenza B and influenza A(H1N1)pdm09.

Influenza transmission in southern China peaked in mid-March and was almost entirely associated with influenza A(H1N1)pdm09.


Countries in the temperate zone of the southern hemisphere

South Africa seems to have an increase in recent weeks in specimens testing positive for influenza with 37.5% testing positive for influenza in week 19, which might indicate the start of the flu season. The vast majority is due to influenza A(H1N1)pdm09. Few influenza B and one influenza A(H3N2) virus were detected in week 18 and 19.

In Australia, New Zealand and the Pacific Islands, ILI activity remained low with few samples testing positive for influenza. During 5 to 11 May 2013 in Australia, of 208 ILI samples received, 1 was positive for influenza A (H1N1) pdm09 and 1 influenza B. In New Zealand, during 5-12 May 2013, influenza activity continued to remain low and below the baseline threshold. Out of 149 samples received 7 were positive for influenza: 3 due to influenza B, 2 to influenza A(H3N2), 1 to influenza A/Perth/16/2009(H3N2), and 1 influenza A(not sub-typed).



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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