Abstract
Understanding how the geographic distribution of and movements within a population influence the spatial spread of infections is crucial for the design of interventions to curb transmission. Existing knowledge is typically based on results from simulation studies whereas analyses of real data remain sparse. The main difficulty in quantifying the spatial pattern of disease spread is the paucity of available data together with the challenge of incorporating optimally the limited information into models of disease transmission. To address this challenge the role of routine migration on the spatial pattern of infection during the epidemic of 2009 pandemic influenza in England is investigated here through two modelling approaches: parallel-region models, where epidemics in different regions are assumed to occur in isolation with shared characteristics; and meta-region models where inter-region transmission is expressed as a function of the commuter flux between regions. Results highlight that the significantly less computationally demanding parallel-region approach is sufficiently flexible to capture the underlying dynamics. This suggests that inter-region movement is either inaccurately characterized by the available commuting data or insignificant once its initial impact on transmission has subsided.
Highlights
The global 2009 A/H1N1pdm outbreak gave rise to an epidemic in England characterised by two distinct waves of infection, occurring, atypically, in summer and in late autumn of 2009, outside of the traditional flu season
The model includes a transmission component that feeds newly infected individuals into a disease and reporting component describing the progress of infected individuals to symptomatic illness and the mechanisms through which this illness is reported to the healthcare system
The MR model results presented here assume a model variant that has density dependence according to the size of the regional population; an assumption of random commuting; and an empirical-based seeding for the number of infections prior to the start date of May 1st 2009, the so-called ‘extended empirical’ seeding described in Supplementary Information (SI) Section 1.4.3
Summary
The global 2009 A/H1N1pdm outbreak gave rise to an epidemic in England characterised by two distinct waves of infection, occurring, atypically, in summer and in late autumn of 2009, outside of the traditional flu season. We consider two types of model: a parallel-region (PR) model, where epidemics in different regions are assumed to occur in isolation, but are described by models with some common parameters; and a meta-region (MR) model, where the epidemic acts on a single population, stratified by age and region, with the populations from each stratum interacting through commuter flux We use these approaches to explore the spread of the first two waves of 2009 pandemic influenza across England, estimating their dynamic characteristics based on a range of epidemic surveillance data including general practitioner (GP) consultations, seropositivity, virological positivity and case confirmations (see Fig. 1 for the London data)
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