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Review
. 2011 Nov;5(6):e487-98.
doi: 10.1111/j.1750-2659.2011.00249.x. Epub 2011 Apr 20.

Epidemiologic and Virologic Assessment of the 2009 Influenza A (H1N1) Pandemic on Selected Temperate Countries in the Southern Hemisphere: Argentina, Australia, Chile, New Zealand and South Africa

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Free PMC article
Review

Epidemiologic and Virologic Assessment of the 2009 Influenza A (H1N1) Pandemic on Selected Temperate Countries in the Southern Hemisphere: Argentina, Australia, Chile, New Zealand and South Africa

Maria D Van Kerkhove et al. Influenza Other Respir Viruses. .
Free PMC article

Abstract

INTRODUCTION AND SETTING: Our analysis compares the most comprehensive epidemiologic and virologic surveillance data compiled to date for laboratory-confirmed H1N1pdm patients between 1 April 2009 - 31 January 2010 from five temperate countries in the Southern Hemisphere-Argentina, Australia, Chile, New Zealand, and South Africa.

Objective: We evaluate transmission dynamics, indicators of severity, and describe the co-circulation of H1N1pdm with seasonal influenza viruses.

Results: In the five countries, H1N1pdm became the predominant influenza strain within weeks of initial detection. South Africa was unique, first experiencing a seasonal H3N2 wave, followed by a distinct H1N1pdm wave. Compared with the 2007 and 2008 influenza seasons, the peak of influenza-like illness (ILI) activity in four of the five countries was 3-6 times higher with peak ILI consultation rates ranging from 35/1,000 consultations/week in Australia to 275/100,000 population/week in New Zealand. Transmission was similar in all countries with the reproductive rate ranging from 1.2-1.6. The median age of patients in all countries increased with increasing severity of disease, 4-14% of all hospitalized cases required critical care, and 26-68% of fatal patients were reported to have ≥1 chronic medical condition. Compared with seasonal influenza, there was a notable downward shift in age among severe cases with the highest population-based hospitalization rates among children <5 years old. National population-based mortality rates ranged from 0.8-1.5/100,000.

Conclusions: The difficulty experienced in tracking the progress of the pandemic globally, estimating its severity early on, and comparing information across countries argues for improved routine surveillance and standardization of investigative approaches and data reporting methods.

Figures

Figure 1
Figure 1
The figures illustrate virus circulation by strain [pandemic H1N1, influenza A (not subtyped), and total seasonal influenza A] and the percent of all specimens tested that are positive for influenza over time by country. **Data sources include available virus isolate data from sentinel and non‐sentinel systems; graphs include all national isolate data (NZ, SA, Chile, Argentina), or a subset of all available data (Australia).
Figure 2
Figure 2
(A) Weekly Number of influenza‐like illness Consultations 2007–2009 by country. Data sources vary by country and include: primary health care centres/national sentinel surveillance system (Argentina/Chile); national general practitioner (GP) sentinel surveillance system (New Zealand); and national GP sentinel surveillance system (Australia) N.B. differences in scale in the Y axis. (B) Inpatient and outpatient hospital consultations for influenza (ICD 10) 2007–2009 in South Africa. Data source includes sentinel surveillance from private hospitals in four provinces (South Africa).

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