Excess Mortality in England and Wales, and in Greater London, During the 1995 Heatwave
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J Epidemiol Community Health: first published as 10.1136/jech.52.8.482 on 1 August 1998. Downloaded from 482 J Epidemiol Community Health 1998;52:482–486 Excess mortality in England and Wales, and in Greater London, during the 1995 heatwave Cleone Rooney, Anthony J McMichael, R Sari Kovats, Michel P Coleman Abstract predominantly conducted in the US, have Study objective—To assess the impact on shown that those most vulnerable to heat- mortality of the heatwave in England and related mortality are the aged and the urban Wales during July and August 1995 and to poor.23 Recently, a case-control study4 of describe any diVerence in mortality im- deaths during the 1995 heatwave in Chicago pact between the Greater London urban identified several categories of vulnerable population and the national population. person. These included people who were bed- Design—Analysis of variation in daily ridden and those living in homes that were mortality in England and Wales and in poorly ventilated or not air conditioned. Greater London during a five day heat- With its relatively stable maritime climate, wave in July and August 1995, by age, sex, temperature extremes are rarer in England and and cause. Wales than in countries with continental Setting—England and Wales, and Greater climates such as the USA. Although increases London. in summertime daily mortality during “hot Main results—An estimated 619 extra spells” have previously been documented,56 deaths (8.9% increase, approximate 95% there have been few quantitative assessments of confidence interval 6.4, 11.3%) were ob- heat-related mortality in the UK or of determi- served during this heatwave in England nants of vulnerability to heatwaves here. and Wales, relative to the expected number of deaths based on the 31-day Death rates in England and Wales oscillate seasonally, being lower in summer than in win- moving average for that period. Excess 7 deaths were apparent in all age groups, ter months. In temperate countries, the daily most noticeably in women and for deaths number of deaths at any time of the year is from respiratory and cerebrovascular dis- generally lowest within an intermediate range ease. Using published daily mortality risk of daily outdoor temperatures, and there is coeYcients for air pollutants in London, it often a threshold temperature above which was estimated that up to 62% of the excess daily mortality increases steeply.89 The local mortality in England and Wales during threshold temperature varies between popula- the heatwave may be attributable to tions, probably through physiological acclima- concurrent increases in air pollution. In tisation and cultural adaptation in clothing and Greater London itself, where daytime housing,2 and the upturn in daily mortality is temperatures were higher (and with lesser more evident in some populations (for exam- http://jech.bmj.com/ falls at night), mortality increased by ple, Shanghai) than in others (for example, 16.1% during the heatwave. Using the Guangzhou).9 Recent analyses of urban popu- same risk coeYcients to estimate the lations in the USA, Canada, the Netherlands, excess mortality apparently attributable China, and the Middle East indicate that all- to air pollution, more than 60% of the total cause mortality rises during heatwaves.389 excess in London was apparently attribut- Extremes of temperature and air pollution able to the eVects of heat. both cause increases in daily mortality, al- Conclusion—Analysis of this episode though few studies have estimated their on September 29, 2021 by guest. Protected copyright. shows that exceptionally high tempera- independent eVects.3 Increases in levels of OYce for National tures in England and Wales, though rare, ozone, fine particulates, and nitrogen dioxide Statistics, 1 do cause increases in daily mortality. are associated with increases in all-cause daily Drummond Gate, (J Epidemiol Community Health 1998;52:482–486) mortality; ozone particularly aVects respiratory London SW1V 2QQ 10 C Rooney and cardiovascular daily mortality. To eluci- M P Coleman August 1995 was the hottest August in date the extent and nature of the mortality impact of heatwaves in England and Wales, we Department of England and Wales since weather records 1 have analysed data from the exceptionally hot Epidemiology and began in 1659. The hottest day of the year was Population Health, 1 August, when temperatures reached 35.2ºC spell from 30 July to 3 August during the very London School of in Boxworth, Cambridgeshire (data obtained hot summer of 1995. We compared daily Hygiene and Tropical from London Weather Centre, 127 Clerken- deaths during this five-day episode with the Medicine, London well Road, London EC1). For the world as a expected numbers of deaths estimated from A J McMichael whole, 1995 was then the warmest year on recorded daily deaths during 1993–95 in Eng- RSKovats 1 M P Coleman record. land and Wales. We also assessed the extent to In that same 1995 summer, more than 460 which air pollution may have accounted for any Correspondence to: extra deaths were certified as caused by the observed excess mortality during the episode. Dr Rooney. eVects of the extreme heatwave in Chicago in We repeated this analysis for the population of 2 Accepted for publication July, when temperatures reached 40ºC. Stud- Greater London separately, to assess the effects 18 February 1998 ies of death rates during such episodes, of heat and air pollution in a large city. J Epidemiol Community Health: first published as 10.1136/jech.52.8.482 on 1 August 1998. Downloaded from Excess mortality during the 1995 heatwave in the UK 483 Methods is that based on comparison with 1995, From the national mortality database held by although this is marginally more conservative, the OYce for National Statistics, we extracted as the values for heatwave days are included in the daily numbers of deaths by date of death the average values. An approximate confidence (that is, not the date when the death was regis- interval for the excess mortality was obtained tered) for 1993–95. For 1995, we also ex- by treating the total number of deaths during tracted the daily number of deaths by sex, the heatwave as a Poisson variable, and broad age group (0–15 years, 16–64, 65–74, comparing the upper and lower 95% confi- 75–84, 85 and over) and for selected broad dence bounds of this value with the expected categories of cause of death: neoplasms (ICD-9 number of deaths. A slightly less conservative codes 140–239), ischaemic heart disease (410– estimate of the excess mortality during the 414), cerebrovascular disease (430–438), and heatwave can be obtained by assuming that, in respiratory disease (460–519). the absence of the heatwave, the number of Central England Temperature (CET) is a deaths on heatwave days could be estimated by weighted mean temperature for England and linear interpolation between the number of Wales derived from measurements at four dis- deaths on the immediately preceding (29 July) persed meteorological stations (Squires Gate, and succeeding (4 August) days, and re- Lancs; Manchester Airport; Malvern, Worcs; calculating the 31-day moving average values and Rothamsted, Herts) and corrected for for 1995 accordingly. small eVects of urban warming.11 We obtained We obtained daily atmospheric concentra- from the UK Meteorological OYce the daily tions of ozone, respirable fine particulates CET for 1993–95 and daily temperatures for (PM10, particulate matter with diameter <10 London for 1995. microns) and nitrogen dioxide measured at The daily number of deaths from all causes selected sites in England in 1995 from AEA and the daily mean CET were plotted for the Technology (formerly part of the United months of May to September 1995. Similar Kingdom Atomic Energy Authority) at the analyses were carried out for selected causes of National Environmental Technology Centre. death and for each sex and age group. The 31- The monitoring sites included several in inner day moving average values (including the 15 and outer London and both rural and urban days on either side of the index day) for daily sites outside London. To estimate the approxi- mortality were calculated both for 1993 and mate impact of these air pollutants on daily 1994 combined and for 1995. Excess mortality mortality during the 1995 heatwave, we used in the heatwave was assessed as the diVerence the published season-specific risk coeYcients between the number of deaths observed on a derived recently for London10 (there being no given day and the corresponding moving aver- comparable set of coeYcients for either age value, separately for 1993–94 and for 1995. England and Wales as a whole or for areas out- The preferred estimate for the excess mortality side London). These linear coeYcients estimate 1700 http://jech.bmj.com/ 1500 on September 29, 2021 by guest. Protected copyright. 1300 Daily value 1995 Average 1993–94 25 Average 1995 Daily number of deaths 20 1100 15 10 Central England Temperature ( C) 0 1 May 1 June 1 July 1 August 1 September Figure 1 Daily number of deaths in England and Wales and mean daily Central England Temperature (ºC), May to September 1995; with 31-day moving averages for 1993–94 and 1995. J Epidemiol Community Health: first published as 10.1136/jech.52.8.482 on 1 August 1998. Downloaded from 484 Rooney, McMichael, Kovats, et al Table 1 Total and excess deaths in England and Wales during the five-day heatwave in 1995, by age, sex, and cause KEY POINTS x Daily deaths in England and Wales England and Wales Greater London during the 1995 heatwave rose 8.9% Observed Excess deaths Observed Excess deaths above the seasonal average. deaths deaths Number Number % Number Number % x The eVect was greater for respiratory dis- ease (12.4%) and cerebrovascular disease Compared with 1993–94 Compared with 1993–94 (11.3%).