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

Abstract

Please cite this paper as: Van Kerkhove et al. (2011) 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. Influenza and Other Respiratory Viruses 5(6), e487–e498. 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.

Estimating influenza outpatients' and inpatients' incidences from 2009 to 2011 in a tropical urban setting in the Philippines

“…In other countries, the reported incidences of H1N1pdm09 influenza are significantly higher than those of seasonal influenza . In our study, however, the H1N1pdm09 influenza incidence rate in 2009 was comparable with the influenza B incidence rate in 2010, although baseline seasonal influenza rates were unknown because the present study did not cover years prior to 2009.…”

Transmission Characteristics of the 2009 H1N1 Influenza Pandemic: Comparison of 8 Southern Hemisphere Countries

“…South Africa experienced a first wave of seasonal H3N2 influenza followed by H1N1pdm influenza peaking in early August 2009 [6] (Table 1)(Figures 1 and 2). …”

2009 versus 2010 comparison of influenza activity in southern hemisphere temperate countries

“…The H1N1 (2009) pandemic virus began to circulate in most temperate countries of the Southern Hemisphere near the start of their usual seasons of influenza virus transmission in 2009 1 . The H1N1pdm virus quickly became the predominant strain detected, even where other seasonal influenza viruses had already been detected that season.…”

“…Rates of hospitalization and intensive care unit (ICU) admissions because of H1N1pdm, as well as ILI and SARI rates in all five countries, were >2 times higher in 2009 compared with 2010. For example, hospitalization rates in New Zealand in 2010 have been about half those in 2009 (13·8/100 000 11 versus 26·1/100 000, 1 respectively), whereas ICU admissions during 2010 were approximately 75% of that in 2009. In Chile, there have been 1·5/100 000 confirmed cases of H1N1pdm SARI reported up to EW 36 2010 in Chile 9 as compared with 9·5/100 000 in 2009 16 .…”

“…The 2009 influenza season in temperate countries in the southern hemisphere has been well documented as moderately severe in terms of impact on healthcare systems 1–3 . However, experience with previous pandemics has demonstrated that in some cases, the second season of transmission can be worse than the initial one 4 .…”