Influenza Update N° 201, 20 December 2013
- In North America the influenza season has started. The predominant subtype of influenza viruses detected was influenza A(H1N1)pdm09.
- For the rest of the northern hemisphere as well as in the southern hemisphere influenza activity remained low.
- In countries of tropical areas variable influenza activity was reported.
Based on FluNet reporting (as of 19 December 2013, 07:15 UTC), during weeks 48 to 49 (24 November 2013 to 7 December 2013), National Influenza Centres (NICs) and other national influenza laboratories from 89 countries, areas or territories reported influenza surveillance data.
The WHO GISRS laboratories tested more than 42 360 specimens.
3304 were positive for influenza viruses, of which 2816 (85.3%) were typed as seasonal influenza A and 487 (14.7%) as influenza B.
Of the sub-typed seasonal influenza A viruses, 1166 (66.4%) were influenza A(H1N1)pdm09and 591 (33.6%) were influenza A(H3N2).
Of the characterized B viruses, 39 (70.9%) belonged to the B-Yamagata lineage and 16 (29.1%) to the B-Victoria lineage.
For updates on human infections with avian influenza A(H7N9) virus see the WHO website ( and  )
Countries in the temperate zone of the northern hemisphere
Overall influenza activity in North America has increased indicating the start of the season, with A(H1N1)pdm09 viruses predominant.
In Canada influenza-like illness (ILI) and detections of influenza had increased.
In the United States of America, the proportion of visits for influenza-like illness reached the 2% national threshold for the start of the season and the number of samples testing positive for influenza increased to 17%.
Low levels of influenza activity continued. All three influenza subtypes were detected but in low numbers. The number of hospitalizations due to severe acute respiratory infection (SARI) remained at interseasonal level.
Northern Africa and the Western and Central Asia region
Influenza activity was low in the northern African and western and central Asia. Egypt and Jordan reported increased circulation of A(H1N1)pdm09 viruses.
Influenza activity in the northern region of Asia remained low.
In northern China, influenza detections continued to increase but stayed at interseasonal level.
In Mongolia, clinical respiratory illness activity has increased since mid-August though with no influenza viruses detected.
Countries in the tropical zone
Tropical countries of the Americas/Central America and the Caribbean
Overall influenza activity in the Caribbbean, Central America and tropical areas of South America was at low levels. Generally influenza A(H1N1)pdm09 circulated throughout.
In Honduras although ILI activity and SARI-associated hospitalizations decreased, the proportion of SARI–associated deaths increased and of 209 samples tested during weeks 42 to 45, 30.1% were positive for influenza.
Central African tropical region
In the African tropical region, influenza activity was reported from the central and western regions.
In Cameroon 29% of the samples were positive for influenza with mainly influenza B. Cameroon also reported a high number of SARI cases in recent weeks.
Côte d’Ivoire and Ghana reported increased detections of A(H3N2).
Madagascar reported increased ILI activity associated with non-influenza respiratory viruses.
Influenza activity in southern Asia was generally low but increased in some areas. Influenza A(H3N2) virus was the main subtype reported, but A(H1N1)pdm09 and influenza B viruses were also detected in low numbers.
In southern China, influenza activity continued to increase.
In the Islamic Republic of Iran influenza activity increased since mid-November.
Influenza activity in South-East Asia varied among countries but overall remained at moderate levels with A(H3N2) virus predominant.
Activity increased in the Lao People's Democratic Republic and Thailand, remained moderate in Viet Nam, and decreased slightly in Cambodia.
Countries in the temperate zone of the southern hemisphere
In the southern hemisphere the season is over and all indicators are at interseasonal level.
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.