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Short-term effects of ambient temperature on daily deaths and hospital admissions
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Occupational and Environmental Medicine.ORCID iD: 0000-0003-4030-0449
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.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1341
Keyword [en]
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
Identifiers
URN: urn:nbn:se:umu:diva-32906ISBN: 978-91-7264-973-6 (print)OAI: oai:DiVA.org:umu-32906DiVA: diva2:306641
Public defence
2010-04-23, Room 135, Family medicine, Umeå University, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2010-04-01 Created: 2010-03-30 Last updated: 2015-04-29Bibliographically approved
List of papers
1. The effect of temperature on mortality in Stockholm 1998-2003: a study of lag structures and heatwave effects
Open this publication in new window or tab >>The effect of temperature on mortality in Stockholm 1998-2003: a study of lag structures and heatwave effects
2008 (English)In: Scandinavian Journal of Public Health, ISSN 1403-4948, E-ISSN 1651-1905, Vol. 36, no 5, 516-523 p.Article in journal (Refereed) Published
Abstract [en]

AIMS: To describe seasonal patterns of natural mortality in Stockholm as well as the temperature-mortality relationship and the lag structure for effects of high and low temperatures; to describe the impact of high temperatures on cardiovascular and respiratory mortality, and the general effect of high temperatures in different age groups; and to investigate whether there is any indication of an additional heatwave or cold spell effect.

METHODS: Generalized additive Poisson regression models were fitted to mortality and temperature data from Stockholm from the period 1998-2003, controlling for influenza, season, time trends, week day, and holidays.

RESULTS: The mortality in Stockholm followed a seasonal pattern, with a peak in the winter season. The ;;optimal temperature'' was around 11-12 degrees C. Above this temperature, the cumulative general relative risk (RR) corresponded to a 1.4% (95% confidence interval (CI)=0.8-2.0) increase per degrees C, and below this temperature the cumulative RR corresponded to a 0.7% (95% CI=0.5-0.9) decrease per degrees C. Age-specific RRS were estimated above the threshold for age <65 years, age 65-74 years, and age >74 years, with estimated increases of 0.5% (not significant), 1.5% (not significant) and 1.6% (95% CI=0.9-2.3) per degrees C, respectively. The RRs for cardiovascular and respiratory causes were studied above the breakpoint, and estimated to be 1.1% (95% CI=0.3-2.0) and 4.3% (95% CI=2.2-6.5) per degrees C, respectively. The lag structures from moving averages and polynomial distributed lag models coincided with a rather direct effect during summer (lag 0 and 1) and a more prolonged effect during winter, covering about a week. The inclusion of an indicator of heatwaves added an increase in daily mortality of 3.1-7.7%, depending on the threshold.

CONCLUSIONS: These results show that the predicted increase in heat events must also be taken seriously in Scandinavia, whatever the extent of the decreasing cold related mortality. The relative risks associated with heat and heatwaves seem stronger than the cold effects and thus a larger public health threat, since northern populations have not yet adapted to heat as have been done over a long time for the cold periods. The pressure on the healthcare sector will probably increase in the warm season, periodically it may become even greater than the pressure due to cold weather, which will be a new phenomenon for the healthcare sector to cope with. We need to be prepared for these kind of events by developing adaptation and education strategies to handle the consequences that a warmer climate will have for public health and the healthcare sector.

National Category
Environmental Health and Occupational Health
Identifiers
urn:nbn:se:umu:diva-18792 (URN)10.1177/1403494807088458 (DOI)18567653 (PubMedID)
Available from: 2009-02-25 Created: 2009-02-25 Last updated: 2017-12-13Bibliographically approved
2. Winter mortality modifies the heat-mortality association the following summer
Open this publication in new window or tab >>Winter mortality modifies the heat-mortality association the following summer
2009 (English)In: European Respiratory Journal, ISSN 0903-1936, E-ISSN 1399-3003, Vol. 33, no 2, 245-251 p.Article in journal (Refereed) Published
Abstract [en]

The present study aimed to investigate how the heat-related increase in deaths in summer and the extent of mortality displacement depend on influenza and other categories of mortality in the previous winter, which when low leaves a greater pool of susceptible individuals. Mortality data from Stockholm, Sweden, from 1990-2002 were stratified into a summer period and a winter period. A Poisson regression model was established for the daily mortality in the summer, with temperature and confounders as explanatory variables. In addition, indicators of total, respiratory, cardiovascular and influenza mortality of the winter period were incorporated as effect modifiers in the summer model, and lagged effects in strata defined by indicators were studied. A high rate of respiratory as well as cardiovascular mortality in winter reduced the heat effect the following summer, and influenza mortality tended to do so as well. The cumulative effect per degrees C increase was 0.95% below and 0.89% above a threshold (21.3 degrees C) after a winter with low cardiovascular and respiratory mortality, but -0.23% below and 0.21% above the threshold after a winter with high cardiovascular and respiratory mortality. The current study shows that high respiratory, cardiovascular and influenza mortality in winter leads to lower temperature effects in the following summer. It also suggests that persons for whom influenza may be fatal are often also susceptible to heat and this subgroup might, therefore, not benefit as much as expected from influenza vaccinations.

National Category
Environmental Health and Occupational Health
Identifiers
urn:nbn:se:umu:diva-19678 (URN)10.1183/09031936.00037808 (DOI)18799511 (PubMedID)
Available from: 2009-03-09 Created: 2009-03-09 Last updated: 2017-12-13Bibliographically approved
3. Comparing approaches for studying the effects of climate extremes: a case study of hospital admissions in Sweden during an extremely warm summer
Open this publication in new window or tab >>Comparing approaches for studying the effects of climate extremes: a case study of hospital admissions in Sweden during an extremely warm summer
2009 (English)In: Global Health Action, ISSN 1654-9716, E-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.

Keyword
hospital admission; temperature; heat; surveillance; weather; climate change; extreme event
National Category
Environmental Health and Occupational Health
Identifiers
urn:nbn:se:umu:diva-30746 (URN)10.3402/gha.v2i0.2034 (DOI)
Available from: 2010-01-14 Created: 2010-01-14 Last updated: 2017-12-12Bibliographically approved
4. Contrast in mortality related to temperature and persistent temperature extremes: a study of cause-specific and age stratified mortality
Open this publication in new window or tab >>Contrast in mortality related to temperature and persistent temperature extremes: a study of cause-specific and age stratified mortality
(English)Article in journal (Other academic) Submitted
National Category
Environmental Health and Occupational Health
Identifiers
urn:nbn:se:umu:diva-32977 (URN)
Available from: 2010-04-01 Created: 2010-04-01 Last updated: 2014-01-23Bibliographically approved
5. Mortality related to temperature and persistent temperature extremes: a study of potential susceptibility factors
Open this publication in new window or tab >>Mortality related to temperature and persistent temperature extremes: a study of potential susceptibility factors
(English)Manuscript (preprint) (Other academic)
National Category
Environmental Health and Occupational Health
Identifiers
urn:nbn:se:umu:diva-32978 (URN)
Available from: 2010-04-01 Created: 2010-04-01 Last updated: 2015-04-29Bibliographically approved

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