Update number 146

Table of contents

- Summary
- Countries in the temperate zone of the northern hemisphere
- Countries in the tropical zone
- Countries in the temperate zone of the southern hemisphere
- From the peer-reviewed literature
- Virological surveillance

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Please note that a summary report of the 2010 influenza season of the southern hemisphere is available in the WHO Weekly Epidemiological Record (WER), 28 October 2011, vol. 86, 44 (pp 480–496).

Summary

? Influenza activity in the temperate regions of the northern hemisphere remains low or undetectable.
? Low level influenza activity is reported in the tropical zone in a few countries of the Americas (Cuba, Dominican Republic and Honduras), central Africa (Cameroon), and Southern and Southeast Asia (Cambodia, Thailand, Lao People´s Democratic Republic and Viet Nam).
? Transmission in South Africa and South America remains low.

Countries in the temperate zone of the northern hemisphere

The countries in the northern hemisphere temperate zone are still in their inter-seasonal period for influenza. The majority of the countries in this zone reported low or no influenza activity, although sporadic influenza virus detection has been reported in recent weeks.

Countries in the tropical zone

• Southern Asia circulation of influenza viruses (snapshot)
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In the tropical countries of the Americas, generally low levels of influenza transmission were reported. In the Caribbean, low level transmission of different influenza viruses has been reported in the Dominican Republic (influenza type B) and Cuba (influenza A(H3N2)) both of which experienced transmission peaks 2 to 3 months earlier. In Central America, Honduras and El Salvador have both reported recent peaks in transmission of influenza A(H3N2), which is now decreasing. Nicaragua, however, has reported recent sharp increases detection of influenza A(H1N1)pmd09 with a total of 199 cases confirmed between mid to late September and mid to late October 2011. Panama, has been consistently reporting low numbers of H1N1pdm since late June with a peak occurring in August. Other Central American countries and countries of the tropical area of South America have reported low or undetectable levels of influenza transmission.

In sub-Saharan Africa, influenza transmission has generally remained low with the exception of Cameroon where influenza A(H1N1)pdm09 and type B has continued to co-circulate at peak levels in recent weeks.

Low levels of influenza transmission has continued to be reported in tropical Asia following transmission peaks that occurred one to two months ago. Transmission of influenza A(H3N2) peaked in India, Bangladesh and Thailand in the period from late July (India and Bangladesh) to early September (Thailand and Lao People´s Democratic Republic) but was followed by a secondary increase in influenza type B circulation. Small amounts of influenza type B has continued to be detected in the area since. Notably, surveillance in flood shelters of central Thailand, where large areas have been flooded, reported influenza-like illness (ILI) to be the predominant illness detected. The influenza surveillance systems in the country have recently reported large numbers of H3N2 and influenza type B detections. In contrast to the other countries of southern Asia, Viet Nam continues to report sustained transmission of influenza A(H1N1)pdm09 with much smaller numbers of influenza type B, which has been continuous since the beginning of 2011, and Cambodia reports an almost even mix of influenza type B and influenza A(H1N1)pdm09.

Countries in the temperate zone of the southern hemisphere

South America

• Temperate South America circulation of influenza viruses (snapshot)
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In the temperate regions of South America influenza transmission continued to decline, approaching intra-seasonal levels. Small amounts of influenza A(H3N2) and A(H1N1)pdm09 co-circulate in Chile, while influenza transmission in other countries in South America continued at low or undetectable levels.

Southern Africa

• Southern Africa circulation of influenza viruses (snapshot)
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Influenza transmission in South Africa has continued at low levels since peaking in early June.

Australia, New Zealand and South Pacific

• Oceania Melanesia and Polynesia circulation of influenza viruses (snapshot)
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Influenza activity continued to decrease in Australia and New Zealand with the season appearing largely over. However, there are regional variations in timing and differences in subtypes.

In New Zealand, the rate of national ILI consultations decreased to 10.7 per
100 000 patient population (39 ILI consultations), with the ILI consultation levels being maintained below the baseline. In New Zealand in 2011, 1 269 influenza viruses were confirmed: influenza type B (594), A(H1N1)pdm09 (108), A(H3N2) (430) and influenza A (not subtyped) (137). The circulating influenza strains are covered by the current influenza vaccine.

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