Research
Long-term effects of flooding on mortality in England and Wales, 1994-2005: controlled interrupted time-series analysis
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* Corresponding author: Ai Milojevic ai.milojevic@lshtm.ac.uk
1 Department of Social and Environmental Health Research, London School of Hygiene and Tropical Medicine, 15-17 Tavistock Place, London WC1H 9SH, UK
2 Environment Agency, Bowbridge Close, Bradmarsh Business Park, Templeborough, Rotherham, South Yorkshire, S60 1BY, UK
3 Centre for Radiation, Chemicals and Environmental Hazards, Health Protection Agency, 7th Floor, 330 High Holborn, London WC1V 7PP, UK
Environmental Health 2011, 10:11 doi:10.1186/1476-069X-10-11
Published: 2 February 2011Abstract
Background
Limited evidence suggests that being flooded may increase mortality and morbidity among affected householders not just at the time of the flood but for months afterwards. The objective of this study is to explore the methods for quantifying such long-term health effects of flooding by analysis of routine mortality registrations in England and Wales.
Methods
Mortality data, geo-referenced by postcode of residence, were linked to a national database of flood events for 1994 to 2005. The ratio of mortality in the post-flood year to that in the pre-flood year within flooded postcodes was compared with that in non-flooded boundary areas (within 5 km of a flood). Further analyses compared the observed number of flood-area deaths in the year after flooding with the number expected from analysis of mortality trends stratified by region, age-group, sex, deprivation group and urban-rural status.
Results
Among the 319 recorded floods, there were 771 deaths in the year before flooding and 693 deaths in the year after (post-/pre-flood ratio of 0.90, 95% CI 0.82, 1.00). This ratio did not vary substantially by age, sex, population density or deprivation. A similar post-flood 'deficit' of deaths was suggested by the analyses based on observed/expected deaths.
Conclusions
The observed post-flood 'deficit' of deaths is counter-intuitive and difficult to interpret because of the possible influence of population displacement caused by flooding. The bias that might arise from such displacement remains unquantified but has important implications for future studies that use place of residence as a marker of exposure.