Atmospheric Emironment Pergamon Press 1970. Vol. 4, pp. 453-465. Printed in Great Britain.

THE INFLUENCE OF CLIMATE AND ATMOSPHERIC POLLUTION ON EXACERBATIONS

OF CHRONIC BRONCHITIS

JMES GREGORY

C.E.G.B. Nuclear Health and Safety Dept., Land House, 70, Newgate St., London, E.C.1.

(Received 9 March 1970)

Abstract-In a retrospective survey, the sickness absence due to exacerbations of chronic bronchitis for 340 frank cases of chronic bronchitis amongst male employees of a Sheffield steel works is compared with climatic factors and atmospheric pollution over a six-year period, from July 1955 to June 1961.

hlonthly average figures for temperature, smoke pollution and sulphur dioxide correlate with monthly sickness rates, but the correlations with air pollution are influenced by the dependence of these two factors on the temperature itself, which on analysis appears as the dominant factor.

Based on weekly averages over the worst winter, the temperature inversely correlates with the prevalence rate of the following week, and both maximum and mean smoke pollution levels correlate with the incidence rate of the succeeding week.

It is concluded that smoke pollution is a factor in the causation of exacerbations, and that temperature may be concerned with the return to work of those already off sick.

SICKLCSS absence records for all cases of chronic bronchitis discovered amongst the male, shop-floor employees of a Sheffield Steel Works were kept over the period July 1955 to June 1961, and details as to climatic factors and atmospheric pollution were obtained for the same period. This retrospective study of these records is an attempt to correlate sickness absence due to exacerbations of chronic bronchitis with these other factors and to draw conclusions as to the effect the latter may have on sufferers

from chronic bronchitis. The steel works concerned is situated in the valley of the river Don in the heart of

the industrial area extending from Sheffield to Rotherham. The area is classed as “an urban area with a population of 100,000 and over”.

The men concerned all lived, at the time of their inclusion in the survey, within the boundaries of Sheffield or Rotherham.

Personnel 1. MATERIAL

During the six years surveyed there were 340 cases of chronic bronchitis. All were of the established disease, suffering from cough, sputum and breathlessness, and having periodic absences from work due to exacerbations.

Twelve of these men were also considered to be suffering from pneumoconiosis, but otherwise the men appeared to be free of other disease. The majority had chest X-rays at least once during the period reviewed.

The pneumoconiosis cases consisted of 8 suffering from silicosis, 3 siderosis and 1 coal-miners’ pneumoconiosis, and all showed the typical history symptoms and signs of chronic bronchitis before nodulation was observed on the chest X-rays. None were considered to be disabled to any degree, or to be losing time from work, because of their pneumoconiosis.

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551 JMES GREGORY

Sickness absence records were kept for all certified absences (i.e., absences of four days and longer) for bronchitis, and interview on return to work ensured as far as practicable that the diagnosis was correct. No limit was set for the period of absence, and the actual weeks lost up to the date of retirement or death were used for those not returning to work. A working year was considered to consist of 50 weeks, each of 6 days.

The sickness absence records were used to provide :

(a) iin incidence rate, defined as the number of new absences due to bronchitis starting in each month (or week, as the case might be), expressed as a percentage of the number of chronic bronchitis cases employed, and

(b) A periodprevalence rate, defined as the number of cases off work due to bron- chitis during the whole or part of each month (or week), expressed as a percentage of the number of chronic bronchitis cases employed.

Climatic factors and atmospheric pollution

The temperature, relative humidity and other climatic factors were recorded at one site, and the smoke pollution and sulphur dioxide levels at eight sites, the average value of the eight readings being used. The location of these sites in relation to the works is shown in APPESDIX I.

The principal records used, averaged over each month (or week, as the case might be), were:

(a) Temperature, in “F, (b) Relative humidity @er cent), (c) Smoke pollution, in milligrammes per 100 cubic metres, and (d) SItlphur dioxide levels in the atmosphere, in parts per 100 million parts of air.

2. RESULTS

Over the 6 years (July 1955 to June 1961) the total population of male, shop-floor personnel (excluding staff) averaged 3708 per year, and the number of sufferers from chronic bronchitis 239 per year. Thus, the prevalence rate averaged 6.4 per 100.

The average age of the 340 chronic bronchitis cases (based on 1958 as the middle of the survey period) was 56.6 years, the range being 19 to 78 years.

Based on a 6 day week of 50 working weeks per year, 8040 weeks were lost from chronic bronchitis over the 6-year period. For an average of 3708 norkers per year this represents a loss of 7.2 man years per 1000 man years employed.

The number of chronic bronchitis cases off sick because of this disease averaged 45 per 1000 employees per year, each losing an average of 8 weeks each year.

The number of spells off work averaged 67 per 1000 employees per year, and the average duration of each spell was 54 weeks.

APPENDIX II gives the incidence and period prevalence rates found and the climatic and pollution conditions, month by month, and these are illustrated in ATPE~DIX III.

Since so many factors are concerned it is difficult to determine the influence, if any, that each may have on the sickness absence rates. By using a multiple regression analysis, which eliminates those factors in turn having least infTuence, the most important factor can be determined.

The Influence of Climate and Atmospheric Pollution on Chronic Bronchitis 455

The correlations obtained between each pair of factors for the monthly averages over the period July 1955 to June 1961, are shown in TABLE 1 (and APPENDIX IV graphs the relationship between the absence rates and temperature).

Good correlations obtain for both the sickness absence rates and most of the climatic and atmospheric pollution factors, but the regression analysis indicates that the tem- perature is the principal factor concerned, the others being temperature dependent to a large extent.

TABLE 1. THE CORRELATION COEFFICIE?rTS BETWEES THf ABSENCE RATES AND CLIMATIC AND ATMOSPHERIC

POLLUTION FACTORS-MONTHLY AVERAGES; JULY 1955 TO JUNE 1961

Sickness absence Period Tempera- Relative Smoke so2 Fog

Incidence prevalence ture humidity pollution levels rate rate

Temperature -0.75 -0.83 - Relative humidity 0.55 0.62 -0.59 - Smoke pollution 0.69 0.63 -0-81 0.56 - SOt levels 0.67 0.61 -0.82 0.48 0.92 - Fog 0.35 (0.19) -0.34 0.39 0.49 0.56 Air frost 0.54 0.61 -0.71 0.30 0.59 O-63 (OT2)

All these correlations, except the two entered within brackets, are significant [i.e. the correlation coefficient (r) is greater than twice the standard error of r].

The analysis eliminated each factor down to this f?nal dominant one with, in the case of the incidence rate, the temperature showing a correlation coefficient of -0.75, such that the mean incidence rate = 32.55 - 0.48 x average temperature (residual SD. 3.5); and, in the case of the period prevalence rate, a correlation coefficient of -0.831 such that the mean period prevalence rate = 59.50-0.830 x average tem- perature (residual S.D. 4.7).

The correlations obtained with the other factors may well be because of their dependence on the temperature, which with each rate appears to have the pre- dominant relationship, with the other factors not affecting the residual variance at the 5 per cent significant level.

During the winter of 1957-1958 the sickness rates reached a higher level than during the previous or later winters, and daily figures were obtained for these rates and the temperature, rainfall, smoke pollution and sulphur dioxide levels for the period 29 September 1957 to 29 March 1958, to determine whether or not there was any correlation to be found between these rates and these different factors over shorter intervals than one month.

It was found impracticable to compare daily fi,wes. The fluctuations from day to day are gross, particularly for the incidence rate since the numbers of new sick vary from 0 to 9 per day, with Mondays showing a high figure and Fridays a low. No records are available for new sickness cases on Saturdays and Sundays, and this, together with the tendency for men to delay going off sick until the weekend if they commence feeling unwell towards the end of a week, gives false high figures for Mondays.

Comparison of weekly averages was therefore decided on, and the figures are

456 JAMES GREGORY

detailed in APPENDICES V and VI. No significant correlations were obtained (set

TABLE 2).

As the period chosen was only one winter it was to be expected rhat the prevafencz rate would show a steady increase, maintained until towards the end of the winter, as the number of cases of long term iliness mounted.

On further study of the graphs depicting the weekly changes (APPENDIX VI), it appeared that the peaks for the weekly incidence rate followed the peaks of smoke concentration and sulphur dio,xide levels by about one week.

If these factors were to affect chronic bronchitis sufferers, then it is to be expected that some short time might elapse before the effects are observable. In addition the high figures of sickr,ess absence to be expected on a Monday, referred to earlier, could well be showing, to some extent, the effect of conditions present the previous week.

TABLE 2 shows the correlations obtained between each pair of factors for the weekly averages over the period 29 September 1957 to 29 March 1958 and the correlations between the absence rates and the climatic and atmospheric pollution factors of the previous week over the same period.

Apart from the expected correlations between smoke pollution, sulphur dioxide levels and fog, only two significant correlations were observed-the period prevalence rate with the temperature of the week before, and the incidence rate with the smoke pollution of the week before.

TABLE~.THECORRELA~ONCOEFFICIESTSBETWEENTHEABSENCE RATESA~~CLIZ~ATIC ANDATSIOSPHERIC POLLUTIONFACTORS-WEEKLY AVERAGES; 29 SEPTEMBER 1957 ~029 MARCH 195s

Sickness absence rates For same week as Of week after that for temperature, etc. temperature, etc.

Incidence Period Incidence Period Tempera- Smoke SO2 prevalence prevalence ture pollution levels Rainfall

Temperature -0.19 -0.36 -0.11 -0.4I - Smoke pollution 0.35 0.1s 0.48 @itI -0.02 - SO2 levels 0.23 0.31 0.34 0.04 -0.32 0.90 - Rainfall 0.24 0.19 0.01 0.25 -0.10 -0.14 -0*15 - Fog 0.04 -0.34 - - 0.24 0.59 0.51 -0.17

Only those five correlations given in bold type are significant [i.e. the correlation coefficient (r) is greater than twice the standard error of rf.

Multiple regression analysis confirmed that these were the dominant relationships. The correlation coefficient between the incidence rate and the smoke pollution of the previous week is 0.48 such that the incidence rate = I.01 + 6.56 x average smoke pollution (residual S.D. 1.5); and that for the period prevalence rate and the temper- ature of the week before is -0-41 such that the period prevalence rate = 25.8 - O-30 x average temperature (residual S.D. 3.2).

The maximum weekly pollution and meteorological findings were not used in the regression analysis since the inter-relationship of the various factors should not be different from that found using the mean weekly figures. But there was found to be a significant correlation (the only one) between the maximum weekly smoke pollution

The I&Iuence of CIimate and Atmospheric Poilution on Chronic Bronchitis 457

and the incidence rate of the succeeding week [correlation coefficient {r) = 0.50, with r/standard error of r = 2.51. APPEXHX VII graphs the relationship between the mean weekly incidence rates and the maximum and mean smoke pollution levels of the previous weeks.

3. DISCUSSION

In a series of 1000 chronic bronchitis cases, 0sw.x~ (1958) gives the answers from patients as to when their symptoms were worst. Eight-hundred and sfty seven said the winter, 744 fog, 698 wet and 435 cold, and as EDWARDS (1962) states “the bron- chitic is not only aware of the aggravating effect of smoking, on his chest condition, but also of climatic variations, particularly in the autumn and winter, and of sudden changes of temperature day by day, and even hour by hour”.

PEMBERTOK (19.52) refers to the “general agreement that the greatest incidence of respiratory disease occurs during the cold months of the year and is inverseIy cor- related with temperature”, as borne out by the work of WOODS (1928).

MILLER (1965) in an investigation of pulmonary function in asthmatics found that “the phenomenon of sensitivity to cold in patients with respiratory disability can be objectively demonstrated under experimental conditions”, and GREENJSURGH et al. (1966) when studying asthma visits to emergency clinics in three New York hospitals showed that there was a marked and significant increase in such visits with the onset of cold weather (outdoor temperature below 55°F) in the month of September,

But as regards chronic bronchitis little work seems to have been done on this aspect of the problem and most of the literature is concerned with air pollution.

Much has been written of the relationship of atmospheric pollution on the incid- ence of, and deaths from, respiratory disease and the Meuse disaster of 1930, the Donora Valley incident of 1948 and the London fogs of 1952 and 1962 are widely quoted. It is generally considered that the worst affected by such extreme conditions are those persons suffering from long-standing respiratory disease, such as chronic bronchitis.

The B.M.J. Leader of 23 February, 1963, compares the fogs in London of 1952 and 1962, which were similar in duration and intensity. That of 1962 had sulphur dioxide concentrations similar to the fog of 1952, but much lower level of smoke pollution, probably 30 per cent less. The 1952 fog was estimated to have killed 4000 people whereas the increased mortality from the 1962 fog was comparatively small, amounting to perhaps 700.

Studies indicate that there is a correlation between high concentrations of atmos- pheric pollution and the morbidity and mortality amongst chronic bronchitics, but opinion would appear to be divided as to the relative effects of smoke and sulphur dioxide, particularly with regard to morbidity, with which this paper is concerned.

SKALPE (1964) showed an increased incidence of respiratory symptoms and a significantly lower average maximal expiratory flow rate in workers exposed to SO2 compared with controls, and DOHAN et al. (1962) found the incidence rates for absence due to illnesses of more than seven days, amongst women in manufacturing plants in eight American cities, were significantly correlated with the “mean suspended partic- ulate sulphate concentrations in the air of the cities in which they worked”.

BURW (1960) considers that sulphur dioxide is more important than the pollution of the air by solid matter, but this is not generally accepted by other workers.

458 JA.WES GREGOR\

WALLER and LATHER (1955) showed that there was a temporary clinical deterioration in some patients with chronic bronchitis and emphysema coinciding with a fog in

London in January 1955. At this time there was a tenfold increase in the smoke con- centration for a 2-hr period, a lesser increase in sulphur dioxide concentration and

no detectable sulphuric acid present.

REID (1958) found the wastage rates among postmen due to premature retirement

due to bronchitis and pneumonia to be highest in large towns and industrial areas. and that this was not due to gradations of climate or temperature. social or occupa-

tional differences. The suspicion that it was due to air pollution was heightened by the fact that there was increased sickness absence in postmen in N.E. London, where the pollution is high. Furthermore, FMRBMRN and REID (1958), in comparing outdoor postmen with indoor office workers, considered that severe bronchitis, with permanent

disablement and death, among the postmen was related to the “frequency of fog and. presumably, to the level of air pollution”, with the bronchitis and pneumonia rates being much higher than amongst the office workers.

WALLER and LAWTHER (1957) correlated the degree of illness of chronic bronchitis

cases (from diaries kept by the patients) with the smoke concentration in Greater London from November 1955 to February 1956, and found that the major peaks in the graph of illness coincided with the peaks of smoke concentration. They found a close association of the clinical condition of 180 patients living in Greater London

with the concentration of atmospheric pollution measured in the City, and the effects of high pollution were not enhanced by dense, wet fog.

In a later investigation along the same lines (LAWTHER, 19593 it was found that fluctuations in the patients’ symptoms closely followed the daily variations in air

pollution, such that when smoke concentrations rose above 30 mg 100 me3 and SO1 above 60 mg 100 mT3 (0.21 ppm) a deterioration of the health of the group of 1000

patients was seen to occur. LAWTHER (1966) sums up the present evidence as regards air pollution and its effects

on chronic bronchitis by pointing out that episodes of especially high pollution result in increased mortality and morbidity, and that such episodes are often referred to by patients as marking, or causing, the onset of their chronic bronchitis.

He considers that in the absence of excesses of disease amongst workers exposed to high concentrations of chemical irritants, the hypothesis that chronic bronchitis is caused by simple chemical irritation is barely tenable, and that there is little convincing evidence to incriminate sulphur dioxide alone.

He favours a combination of pollutants , gaseous or particulate. as being the most

likely culprit rather than a single substance and says that “results to date favour the hypothesis that the substance or combination of substances causing exacerbations of existing chest disease is related more closely to smoke than sulphur dioxide”. and that “there is a greater likelihood that air pollution is the urban factor, or one of the urban factors, involved in the transformation of simple chronic bronchitis into the far more serious infected, complicated phase of the disease”.

In the present survey the relationship of meteorological conditions and air pollu- tion with sickness absence due to bronchitis in sufferers from established chronic

bronchitis is the only aspect studied. Using monthly average figures over a 5 yr period there is a statistically significant

inverse relationship of sickness absence, both as an incidence rate and a period preva-

The Influence of Climate and Atmospheric Pollution on Chronic Bronchitis 459

lence rate, with temperature. Multiple regression analysis suggests that correlations obtained between the other climatic factors and those of air pollution may be due to the temperature dependence of these factors, and indicates that the temperature is the predominant one for both the incidence and period prevalence rates.

Further comparison and analysis of weekly average Ggures for the worst winter provides no correlation between these rates and the various factors for the same week, but does show significant correlations between the incidence rate and both the mean and maximum smoke pollution levels of the previous week, and between the period prevalence rate and the mean temperature of the previous week. Regression analysis confirms that smoke pollution and temperature respectively are the predominant factors.

If exacerbations of chronic bronchitis are influenced by meteorological or air pollution factors it is to be expected that this would be shown with the incidence rather than the prevalence rate. Some delay in the effect is possibte and together with the fact of there being no records for Saturdays and Sundays and the general &ding that the sufferers seem to delay going off sick as long as possible towards the end of the working week, so producing higher numbers of new cases on Mondays than on other days, this suggests that an adverse factor in one week may cause an increase in the incidence rate of the following week.

This was found to be true of smoke pollution, in that significant correlations were present for the incidence rate with both the mean and maximum weekly smoke pol- lution levels of the previous week but with none of the other factors examined. It is to be inferred that smoke pollution has an effect on the incidence of exacerbations of chronic bronchitis, but the number of observations are too few to draw a firm con- clusion.

With regard to the monthly average figures, it may well be that both meteorological and pollution factors influence the sickness absence, but temperature alone would appear to be sufficient to account for the results found.

Temperature also appears to be the only factor correlating with the weekly period prevalence rate of the succeeding week, and therefore appears to be reIated to the number of cases remaining absent due to their bronchitis. Perhaps this relations~p is more concerned with a delay in the return to work of these men, possibly because of a lengthening of the recovery time, or a lack of desire or ability to return to work while the temperature remains low.

ANGEL et al. (1965) investigated respiratory illness in factory and office workers and found the prevalence (i.e. number of men affected each week) of respiratory iliness was more strongly associated with smoke concen~ation than with either sulphur dioxide or temperature, but that the attack rate (number of new illnesses starting each week) was associated equally strongly with smoke and sulphur dioxide.

The results in this survey are not in agreement with the results of these workers, but the close relationship between smoke pollution and exacerbations suggested by both are in agreement with WALLER and LAWTHER’S (1957) findings.

LAW-I-HER’S (1959) figure of 30 mg 100 m -3 of air, as the smoke pollution level at which the deterioration of health was seen to occur, was reached or exceeded on 86 out of the 179 days recorded in this winter of 1957-1958.

On the other hand, the figure of 21 parts per 100 million parts of air for sulphur dioxide levels, quoted in this same context, was reached or exceeded on only 10 days.

460 JAHES GREGORY

It would appear that smoke is more important than sulphur dio‘xide in influencing exacerbations of chronic bronchitis. and this is borne out by the findings during the London fogs of 1952 and I362 and other work referred to earlier, and by the results of this survey.

4. CONCLUSIOxS

Although there are, of course, other factors concerned with the development of exacerbation of chronic bronchitis, notably smoking and infection, the present survey, limited to ciimatic and external environmental factors, does perhaps provide some information of value.

Smoke pollution appears to influence the incidence of exacerbations, with some slight delay before the changes in incidence are noted.

Other factors, such as suiphur dioxide, humidity and temperature do not appear to affect the incidence, except in so far as there is a significantly high correlation between temperature and the average monthly incidence rate.

But temperature, both for the monthly and weekly figures, appears to have a relationship with the period prevalence rate, and it is suggested that this may be because it is more concerned with the return to work of those already off sick; low temperatures delaying return.

Acknowledgements-The meteorological figures %vere provided by Mr. T. H. CLEGG, of the Ci:y lMuseum,Sheffield,and the air poliution figures by Mr. BALEY, of the Sheffield and District Clean Air Committee. I am greatly indebted to both for their help, and also to Dr. D. J. MKIRE and Mr. W. J. ALLUM for their advice and help with the multiple regression analyses.

REFERENCES

ANGEL J. H., FLETCHER C. M., HILL I. D. and TJXKER C. H. (1965) Br. J. Dis. Chest 59,66. British MedicalJournai (Leader) (19631, 1459. BURNS J. L. (1960) J. Coil. G.P.‘s (Symposium on Air Pollution), 3502. DOHAN F. C., EVERTS C. S. and S.&-R. (1962), J. Air Potlut. Control Ass. 12,418. EDWARDS G. F. (1962) in Chronic Bronchi&, Symposium of the Chest and Heart Association, London,

November 1962. FAZRBAIRN A. S. and Rrm D. D. (1958) Br. J. prev. Sot. Med. I2,94. GREENBURGH L., FIEW F., REED J. I. and E--r 6. L. (1966) Archs E~vjron. Hftk 12,561. LA~THER P. 3. (1959) J. Roy. Sot. Hth 79, I. LA~THER P. J. (1966) Postgrud. Med. J. 42, 703. MILLER J. S. (1965) Br. J. dis. Chest 59, 23. OSWALD N. C. (19581 Recent Trends in Chronic Bronchitis Llovd-Luke. London. F%MBERTON J. ((952) iWed. Off. 88, 39. REP D. D. (1958) The LMilroy Lectures, 1957. Lancet 1, 1237 and 1289. SKALPE 1. 0. (1964) Br. 2. industr. Med. 21, 69. WALLER R. E, and LA-R P. J. (1955) Br. Med. J. 2, 156. WALLER R. E. and LAWXER P. J. (1957) Br. Med. J. 2. 1473. WOODS H. M. (1928) Lancer 1,539

The MIuence of Climate and Atmospheric Pollution on Chronic Bronchitis 461

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1357 ,358 1953

APPENDIX III

The Influence of Climate and Atmospheric Pollution on Chronic Bronchitis 465

(a) Incidence rate .

25

I

.

20

I

5-

I I I I I 35 40 45 50 55 60 65 70

Average temperature, OF Average temperature, OF

(b) Period prevalence rote

35 43 45 50 55 60 65 70

APPENDIX V. COMPAIUSON

OF ~t~~~tss AUSENCX wrrtt C~JMA'I'IC tc-vzrotu AND ATMOSPIWUC

POLLUTION, WEEK LIY WEEK, OV~K TIW PEKXW

28 SEFTEMBER

1957~0

29 MAW%

19%

49”8

53

.2

51.5

50

‘7

SO

.5

42.2

%:

4a:s

40.

I 3L

I.7

39.8

iii

7359

14

.3

8.5

21

29

3 9.

9 7.

6 65

16

.2

I I.9

t:3

193

12.2

21

.0

16.2

10

.7

8-7

3&Y

13

9 IS

.6

19.1

::::

19-3

t&

9 f9

.t.l

:;:i

33-2

16.1

Ifs.3

II.5

1.19

I')%

20-2

tn.7

14.X

- 8:P

: 0.

33

0.72

i-8

1 0.

44

- 0.77

I.

21

0.30

u.

07

I .47

I .92

0.

24

0.32

0.

57

u-99

I *

?H

0.4'>

1.53

0.21

ct.35

1’11

Sno

w

lyin

g J:

mua

ry

t&4

and

19-2

s F

ebru

sry

8-9

awl

23-2

8 M

ilrch

X

-IO

.

Muence of Climate and Atmospheric Pollution on Chronic Bronchitis 467

x_-__x %ekly maximum

x--x Weakly meon

No. of days in each week wtth fog fvisbility less than 1100 yd 1

y-_-x Weekly maximum

X-Y Wewkly mean

Weekly per!od x---x prevalence

rate per 100 +.__..Weekly mcldence

rate p*r 100

2 5 Weekly incidence fate

NO”. Dec. .Jan Feb. Mar.

Week commencing 19%

x---X Minimum -x Mean

No. of days in Bach week with enow lying

168 JAMES GREGORY

.

.

.

. .

// /i : ..* .

7 .

1 %* l * . . . l .

0=

Mcxlm~m smoke pollution ;n each week, Mean smoke poilutlon in each week, mg / 100 m3 mg A00 m3

APPENDIX XI