BOX WO-4Influenza Trends, September 2009

Influenza viruses in circulation, 2009: Multiple viral subtypes (influenza A subtypes, pandemic H1N1, and influenza B) circulated throughout 2009 in both the Southern and Northern Hemispheres (Figures WO-12 and WO-13).

Southern Hemisphere influenza season: Several countries experienced multiple viral epidemics that included RSV, parainfluenza, and seasonal influenza (both H3N2 and H1N1); in some cases, 2009-H1N1 influenza A overpowered co-infecting viruses to become the predominant respiratory infection. The following figures, depicting annual influenza trends in Chile (Figure WO-14), Australia (Figure WO-15), Hong Kong (Figure WO-16), Cambodia (Figure WO-17), Kenya (Figure WO-18), South Africa (Figure WO-19), and New Zealand (Figure WO-20), illustrate the significance of 2009-H1N1 influenza A in the Southern Hemisphere 2009 influenza season.

As of September 11, 2009, as the Southern Hemisphere influenza season waned, the following trends in ILI were apparent:

  • Tropical regions: A mixed picture, with some countries showing a decline in activity; others, sustained or increased activity.
  • Temperate regions, Southern Hemisphere: Australia and temperate regions of South America had passed the peak of their winter influenza epidemic; some activity remained due to RSV.
  • Temperate regions, Northern Hemisphere: In Japan, influenza activity exceeded the seasonal epidemic threshold, indicating an early beginning to the annual influenza season. Flu activity was also on the increase in Sweden and several regions of the Russian Federation, but most countries in Europe and Central and Western Asia reported declining activity.

SOURCES: Cox (2009); Fukuda (2009); Shortridge (2009).

FIGURE WO-12. Number of specimens positive for influenza by subtype, Northern Hemisphere, April 19 to August 29, 2009.

FIGURE WO-12Number of specimens positive for influenza by subtype, Northern Hemisphere, April 19 to August 29, 2009

(weeks 17–35). Bars represent the number of specimens reported positive for influenza viruses during the reporting week represented in the x-axis. The x-axis also shows the number of countries that reported to FluNet during the respective week. Example: 17 (38) means that in week 17, 38 countries reported. The right side y-axis shows the proportion (percentage) and the left y-axis shows the absolute number of specimens reported positive for influenza viruses (influenza A subtypes, pandemic H1N1, and influenza B).

SOURCE: Fukuda (2009).

FIGURE WO-13. Number of specimens positive for influenza by subtypes, Southern Hemisphere, April 19 to August 29, 2009.

FIGURE WO-13Number of specimens positive for influenza by subtypes, Southern Hemisphere, April 19 to August 29, 2009

(weeks 17–35). Bars represent the number of specimens reported positive for influenza viruses during the reporting week represented in the x-axis. The x-axis also shows the number of countries that reported to FluNet during the respective week. Example: 17 (7) means that in week 17, 7 countries reported. The right side y-axis shows the proportion (percentage) and the left y-axis shows the absolute number of specimens reported positive for influenza viruses (influenza A subtypes, pandemic H1N1, and influenza B).

SOURCE: Fukuda (2009).

FIGURE WO-14. Number of specimens positive for influenza by subtype, Chile.

FIGURE WO-14Number of specimens positive for influenza by subtype, Chile

SOURCE: Cox (2009).

FIGURE WO-15. Number of specimens positive for influenza by subtype, Australia.

FIGURE WO-15Number of specimens positive for influenza by subtype, Australia

SOURCE: Cox (2009).

FIGURE WO-16. Number of specimens positive for influenza by subtype, Hong Kong.

FIGURE WO-16Number of specimens positive for influenza by subtype, Hong Kong

SOURCE: Cox (2009).

FIGURE WO-17. Number of specimens positive for influenza by subtype, Cambodia.

FIGURE WO-17Number of specimens positive for influenza by subtype, Cambodia

SOURCE: Cox (2009).

FIGURE WO-18. Number of specimens positive for influenza by subtype, Kenya.

FIGURE WO-18Number of specimens positive for influenza by subtype, Kenya

SOURCE: Cox (2009).

FIGURE WO-19. Influenza viral watch sentinel surveillance,* update to end of week 35 (week ending August 30, 2009). Positive samples by influenza types and subtype, South Africa.

FIGURE WO-19Influenza viral watch sentinel surveillance,* update to end of week 35 (week ending August 30, 2009). Positive samples by influenza types and subtype, South Africa

*Virological surveillance at 256 sentinel sites in 9 provinces.

**Detection rate calculated on specimens tested at the National Institute for Communicable Diseases (NICD) only, not shown before onset of season.

SOURCE: Cox (2009).

FIGURE WO-20. Total influenza viruses from sentinel surveillance by type and week reported to August 23, 2009, and the total percentage positive from the swabs received, New Zealand.

FIGURE WO-20Total influenza viruses from sentinel surveillance by type and week reported to August 23, 2009, and the total percentage positive from the swabs received, New Zealand

NOTE: All results of sentinel swabs are received by Environmental Science and Research (ESR). The line shows the proportion of those swabs that test positive for any type of influenza. A low proportion may be due to the swabs not successfully retrieving the virus, or that influenza-like-illness (ILI) presentations to sentinel general practioners (GPs) are due to other viruses.

SOURCE: Reprinted from Lopez and Huang (2009) with permission from the Institute of Environmental Science and Research Limited.

From: Workshop Overview

Cover of The Domestic and International Impacts of the 2009-H1N1 Influenza A Pandemic
The Domestic and International Impacts of the 2009-H1N1 Influenza A Pandemic: Global Challenges, Global Solutions: Workshop Summary.
Institute of Medicine (US) Forum on Microbial Threats.
Washington (DC): National Academies Press (US); 2010.
Copyright © 2010, National Academy of Sciences.

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