Mortality in a General Hospital and Urban Air Pollution

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Summary. A case fatality rate of 9.3 was observed at St. James's Hospital in January 1982. This compares with a mean monthly case fatality rate of 4.6 and a ...
Mortality in a General Hospital and Urban Air Pollution IAN KELLY M.B., B.Ch.

Trinity Medical School Building St. James’s Hospital Dublin 8

LUKE CLANCY M.B., B.Sc., F.R.C.P.I.

Summary A case fatality rate of 9.3 was observed at St. James’s Hospital in January 1982. This compares with a mean monthly case fatality rate of 4.6 and a mean January case fatality rate of 5.3. This increase was compared to the air pollution figures for the relevant period and there was a close match between mortality and air pollution. We believe that this episode of air pollution was a major factor in the excess mortality. An excess mortality was observed in St. James’s Hospital in the winter 1981-1982. The major cause of death during this period was respiratory in nature. No bacteriological or viral epidemics were observed during this period to explain this excess mortality. Recent reports suggest that significant air pollution also occurred in the winter 198l-1982.1 We have investigated this in relation to the excess mortality seen in this hospital.

Methods Statistics relating to monthly mortality and admissions were compiled for the period 1979-1983. The gross mortality figures were examined and then adjusted to allow for varying admission rates. This corrected figure was expressed as a Case Fatality Rate (CFR) Admissions x 100. A monthly mean mortality and CFR were calculated, as were the January mean mortality and CFR. A peak in mortality was seen in January 1982 (Fig. 1). This peak was compared with the monthly mean mortality, mean CFR and the January mean mortality and January CFR for the period 1979-1983. The winter of 1981-1982 was then studied more closely. Monthly mortality rates were resolved

into weekly rates and compared with the mean temperature smoke and SC>2 levels for the same period (Fig 2). Smoke and S02 data was supplied from Dublin Corporation monitoring sites in the city. Levels were expressed as ug/mVweek. Weekly averages were calculated for those sites, corresponding most closely to the catchment area of St. James’s, (Dublin South and South-West). In all, seven sites were used (Table 1). These weekly rates were then further resolved into daily rates for the period January 1982. Mortality was compared with smoke, SO2 levels, temperature and wind speed (Fig. 3).

Results A peak in mortality of 120 was observed for January 1982. This compares with a monthly average of 54 deaths and a January mean mortality of 64. When corrected for admissions and expressed as a CFR, a similar pattern emerged. January 1982 had a CFR of 9.3 as compared with a monthly CFR of 4.6 and a mean January CFR of 5.3. Broadly speaking, there was a two-fold increase in mortality in January 1982. There was an excess number of deaths, from the January mean mortality of 56. When the cause of death was

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examined 66/120 (55%) were respiratory related; 17/120 (14%) died from cardiovascular causes. Although respiratory disease was the predominant cause of death, no bacteriological or viral epidemic occurred at this time. A high average age, 77 years, was noted.

Table 1 Site No 1 2 4 6 11 12 13

Site Locations 156, Dame St. 1973— RDS Ballsbridge 1973Corporation Depot, Rathmines 1973— Garryowen Rd., Ballyfermot 1973— City Laboratory, Cornmarket 1963— Baggot St. Hospital 1973-1979 Cheshire Home, Herbert St. 1980— Bluebell Industrial Estate 1980—

This monthly data was then broken down into weekly fragments. Analysis of this showed this peak to have occurred during the week 14th-20th January (39 deaths). This was preceded immediately by a significant episode of air pollution. When studied on a daily basis, the episode of air pollution is easier to explain. It would appear that a ground based temperature inversion occurred during the week preceding the peak weekly mortality. During the period llth-14th January 1982 exceptionally high levels of air pollution, particularly smoke, were recorded in Dublin. This was due to an atmospheric temperature inversion, forming as a result of very low wind speeds and low surface air temperature over the Dublin area.’ Dispersion of pollutants from the catchment area of St. James’s Hospital was minimal during this period. Daily average concentrations for those sites corresponding to the St. James’s catchment area exceeded 900ug/m3 on two consecutive days, for smoke, and 250 ug/m3 on three days for S02. Individual sites within the grid had even higher daily averages, some exceeding 1400 ug/m3 for smoke and 350 ug/m3 for S02.

Discussion The immediate health effects of a rise in air pollution are well established. These have been demonstrated by an increase in the number of exacerbations of chronic bronchitis;2 increases in sickness absence benefit;3 increases in hospital bed demand;4 and most importantly, by increase in mortality among patients already suffering from chronic respiratory disease.5,6 There is no doubt about these immediate harmful effects. Epidemiological studies point to a causal relationship. The young and elderly are among those most vulnerable to these adverse effects.7 We observed an excess mortality of 56 in January 1982 at St. James’s Hospital, resulting in a doubling of CFR. There was a close temporal relationship between the peak in weekly rates and a preceding episode of air pollution. The recurrent episodes of air pollution and excess mortality observed in London during the

1950s and early 1960s have shown that levels of air pollution, especially when combined with cold weather, affect those already disabled by disease of the lung and heart.7 In Dublin, some evidence of adverse health effects were demonstrated in the mid 1970s. One such study suggests that during unfavourable weather conditions, the level of air pollution may have had serious deleterious health effects in terms of sickness and morbidity of a respiratory nature.8 These and other experiences would suggest a causal relationship between the episode of air pollution in Dublin and the excess mortality seen in our hospital. It is not fully understood how air pollution causes death in patients with chronic respiratory disease, but more recent reports suggests that adverse health effects are associated principally with particulate matters and to a lesser extent S02.9 The W.H.O. guidelines for health protection from air pollution are 100-150 ug/m3/day

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for both smoke and SO2. Excess morbidity and mortality in the elderly with chronic respiratory disease are seen at levels of 250-500 ug/m3/day.10 The levels of air pollution monitored in the catchment area of St. James’s during January 1982, exceeded the levels above which morbidity and mortality are seen. In all, the episode lasted four days. It produced composite averages for the grid that exceeded 900 ug/m3/day for smoke on two consecutive days and 250 ug/m3/day for SO2 on three days. Individual sites within the grid registered smoke levels over 1400 ug/m3/day and SO2 levels over 350 ug/m3/day. We believe that the excess mortality seen was related to this episode of air pollution. The simultaneous period of sub-zero temperatures undoubtedly had a contributory effect.

Acknowledgements We would like to thank Dublin Corporation and the Metereological Service for their assistance in compiling data for this paper. We would also like to thank Ms. Linda Dromgoole for her typing services. We are most grateful to Mr. Michael Bailey of An Foras Forbartha for his advice and help in the writing of this paper. References 1 Bailey ML. Air quality in Ireland: recent trends in atmospheric emissions and concentrations. An Foras Forbartha 1983. 2 Lawther PJ. Air pollution and exacerbations of bronchitis. Thorax 1970; 25: 525-39. 3 Angel JH. Respiratory illness in factory and office workers. Br J Dis Chest 1965; 59: 66-80. 4 Holland WW. The urban factor in chronic bronchitis. Lancet 1965; 1: 445-8. 5 Gardner MJ. Patterns of mortality in middle and old age in county boroughs in England and Wales. Brit J Prev Social Medicine 1969; 23: 133-40. 6 Ministry of Health. Mortality and morbidity during the London fog of 1952. Report of Public and Medical Subjects. London: HMSO, 1954; No. 95. 7 Royal College of Physicians; Air pollution and health. London: London Pitman Medical, 1970. 8 Bailey ML. Air pollution and social welfare claims. Ir J of Environm Sci 1981; 1; 2: 51-7. 9 Schimmel H. J Air Pollut Control Assoc 1975; 25: 739-40. 10 WHO. Sulphur oxides and suspended particulale matter environmental health criteria No. 8, Geneva, 1979.

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