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Comparing approaches for studying the effects of climate extremes: a case study of hospital admissions in Sweden during an extremely warm summer
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Occupational and Environmental Medicine.ORCID iD: 0000-0003-4030-0449
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Occupational and Environmental Medicine.
2009 (English)In: Global health action, ISSN 1654-9880, Vol. 2Article in journal (Refereed) Published
Abstract [en]

Background: Health effects induced by climate, weather and climatic change may act directly or indirectly on human physiology. The future total burden of global warming is uncertain, but in some areas and for specific outcomes, mortality and morbidity are likely to increase. One likely effect of global warming is an increasing number of extreme weather events, such as floods, storms and heat waves. The excess numbers of specific health outcomes attributable to climate-induced events can be estimated. This paper compares approaches for estimating excess numbers of outcomes associated with climate extremes, exemplified by a case study of hospital admissions during the extremely warm summer of 2006 in southern Sweden.

Materials and methods: Daily hospital admission data were obtained from the Swedish National Board of Health and Welfare for six hospitals in the Skåne region of southern Sweden for the period 1998 to 2006. Daily temperature data for the region were obtained from the meteorological station in the city of Malmö. We used four established approaches for estimating the daily excess numbers associated with extreme heat. Time series of daily event rates were assumed to follow a Poisson distribution. Excess event rates were compared by using several approaches, such as standardised event ratios and generalised additive models to estimate the health risks attributable to the extreme climate event.

Results: The four approaches yielded vastly different results. The estimates of excess were considerably biased when not accounting for time trends in previous years’ data. Three of four approaches showed a significant increase in excess hospitalisation rates attributable to the heat episode in Skåne in 2006. However, modelling the effect of temperature failed to describe the risks induced by the extreme heat.

Conclusion: Estimates of excess events depend greatly on the approach used. Further research is needed to identify which method yielded the most accurate estimates. However, one of the approaches used generally seem to perform better than the others in estimating the excess rates associated with the heat episode. Further on, estimating relative risks of temperature or other determinants of disease may fail to incorporate the unique characteristics of particular weather events, such as the effect caused by very persistent heat exposure. Unless this can be incorporated into predictive models, such models may be less appropriate to use when predicting the future burden of heat waves on human health.

Place, publisher, year, edition, pages
2009. Vol. 2
Keyword [en]
hospital admission; temperature; heat; surveillance; weather; climate change; extreme event
National Category
Environmental Health and Occupational Health
URN: urn:nbn:se:umu:diva-30746DOI: 10.3402/gha.v2i0.2034OAI: diva2:286477
Available from: 2010-01-14 Created: 2010-01-14 Last updated: 2015-04-29Bibliographically approved
In thesis
1. Short-term effects of ambient temperature on daily deaths and hospital admissions
Open this publication in new window or tab >>Short-term effects of ambient temperature on daily deaths and hospital admissions
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Background: Incidence of death and hospitalizations have been observed to depend on short-term changes in weather and to increase with extreme temperatures. This thesis aims to strengthen the scientific knowledge on the relationship between temperature and daily deaths, but also the relationship between temperature and daily hospital admissions.

Methods: We constructed time series regression models using daily counts of death and daily weather from the Stockholm area incorporating adjustment for potential confounding factors, season, and long-term time trends. From these models, we established the short-term relationship with daily temperatures and the associated relative risks on daily deaths allowing for a delay between exposure and subsequent deaths. Daily hospital admissions and daily temperatures were analyzed correspondingly using data from Skåne.

Results: Hot and cold temperatures significantly impact on mortality rates as well as rates of hospitalization in Sweden. We found an immediate heat effect on daily deaths, while the impacts of cold temperatures were delayed up to a week after exposure. Cold-related deaths are generally cardiovascular in nature, while deaths resulting from warm temperatures are cardiovascular, respiratory as well as non-cardiorespiratory in nature. The impacts following a heat wave appear to increase proportionally with the length of the extreme hot conditions. The results suggest that the population aged 45 years and older is the main group at elevated risk of death when exposed to high and low temperatures. Moreover, the results suggest that there are several factors of susceptibility on an individual basis that correspond to larger relative risk with high and/or low temperatures.

Daily hospitalisations increased in particular among individuals with respiratory illnesses during extreme persistent heat, whereas high temperatures in general have little impact. In contrast, hospitalizations increased for up to two weeks following exposure to cold temperatures.

Conclusions: The health impacts related to temperature are a serious concern and the attributed impacts are likely to increase to some extent in the future due to an ageing population. Public health preventive strategies should be developed to prevent health consequences related to heat waves and cold temperatures. Future studies should aim at identifying susceptible individuals with elevated death risk at hot and cold ambient temperature conditions.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2010. 70 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 1341
temperature, humidity, weather, climate, climate change, hot, heat, cold, cold spell, cold wave, heat wave, health, hospitalization, hospital admission, death, mortality, morbidity, epidemiology, environmental epidemiology, time series
National Category
Public Health, Global Health, Social Medicine and Epidemiology
Research subject
Occupational and Environmental Medicine
urn:nbn:se:umu:diva-32906 (URN)978-91-7264-973-6 (ISBN)
Public defence
2010-04-23, Room 135, Family medicine, Umeå University, Umeå, 13:00 (English)
Available from: 2010-04-01 Created: 2010-03-30 Last updated: 2015-04-29Bibliographically approved

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