Estimation of the reproductive number for the 2009 pandemic H1N1 influenza in rural and metropolitan New South Wales

Objective: During the early stages of pandemics, when resource planning occurs, the epidemiological parameters of the agent are often poorly described. These estimates are typically derived from metropolitan centres. This paper examines the spread of the 2009 pandemic H1N1 virus in rural and regional New South Wales compared with metropolitan centres. Design: Retrospective statistical analysis of longitudinal data. Setting: Ecological examination of spread of influenza in the general community of New South Wales, Australia. Participants: Number of notified infections with novel pandemic H1N1 influenza in rural/regional (n=241) and metropolitan (n=1788) health service areas of New South Wales during the period 1 June 2009 and 12 July 2009. Main outcome measures: A comparison of the reproductive number for the 2009 pandemic H1N1 in rural/regional and metropolitan New South Wales. Results: The reproductive number of the pandemic H1N1 in rural New South Wales was 1.26 (95% confidence interval (CI), 1.22-1.30) compared with estimates of metropolitan New South Wales of 1.28 (95% CI, 1.26-1.30). This difference was not statistically significant (P=0.314). These estimates are lower than those previously published and of the order of magnitude typically observed with seasonal flu. This was consistent with the clinical observations in Greater Southern Area Health Service. Conclusion: The apparent invariance in the rate of spread of influenza between rural and metropolitan areas should provide rural health care providers with confidence in metropolitan derived estimates when planning in future influenza pandemics.5 page(s