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The influence of climate and atmospheric pollution on exacerbations of chronic bronchitis∗
Armospheric Etiironmenr
Pergamon Press 1971. Vol. 5, pp. 435136. Printed in Great Britain.
DISCUSSION THE INFLUENCE
OF CLIMATE
ON EXACERBATIONS
AND A~OSP~E~C
OF CHRONIC
POLL~ION
BRONCHITIS*
Tms interesting paper examines a topic which has concerned specialists in chronic respiratory disease for a number of years. Detailed analysis of retrospective data on sickness absence for chronic bronchitis in relation to temperature, humidity, and smoke and sulphur pollution suggests two principal conclusions: firstly, that smoke appears to be more important than sulphur dioxide in influencing exacerbations of chronic bronchitis; and secondly, that temperature may influence return to work, either by delaying recovery or because low temperature results in a lack of desire or inability to resume work. While I accept both findings as valuable hypotheses, it is however necessary to point out a number of weaknesses both in the method of analysis and in the data used. In the first place, the data is analysed solely by multiple regression analysis, and no attempt is made to eliminate the possible effect of large-scale seasonal fluctuations. Both temperature and pollution levels vary directly with the time of year, and any correlation involving these variables may simply reveal seasonal variation, which could be due to one or a number of other factors-the obvious one being liability to respiratory infection, though changes in patterns of behaviour could also be responsible. This problem has already been dealt with in some detail and a suitable method of analysis has been developed (HOLLAND et&, 1961; HOLLAND and SPICER, 1966). My second reservation about this paper concerns the prevalence and incidence rates used, which are not truly related to the population at risk. This is, of course, a problem found in all studies based on industrial sickness absence records, since the survey group differs from the general population in both age and sex, and probably also in general fitness. In addition, no attempt is made to allow for the influence of personal or other environmental factors which may well contribute to exacerbations in chronic bronchitis. It is, for example, very possible that cigarette smoking habits may have changed over the 6-yr study period. Finally, the definition of chronic bronchitis used in the study is not precisely stated. A number of studies have shown considerable variability in the use of this diagnosis and have clearly demonstrated the need to adopt a standard definition of this condition. The relationship between atmospheric pollution and chronic respiratory disease is extremely complex, as all investigators of this subject must be aware. The collection of accurate and adequate data on all the relevant factors may in some situations present insuperable problems, and some form of compromise will sometimes have to be reached. Nevertheless, I feel that in this paper the author does not appear to have fully appreciated all the difficulties involved. St. Thhomas' Hospital ~edicai School, London, S.E.1
W. S.‘. HOLLAX~
AUTHOR’S REPLY Clinical involvement with pneum~oniosis and chronic bronchitis since 1946 has made me only too aware of the complexity of the problems in assessing the various factors associated with both the morbidity and mortality of the latter disease. However, I am no statistician and anv statistical failinas must be put down to the fact that the material was extracted from old records with statistical hej;) coming late and, of necessity, no statistical preplanning. This work was part of a larger retrospective survey of clinical records (to be publ~hed in the Archives ofEnvironmentalHealrh), and it was only whilst studying these I realised that I had a complete record of all the sickness absence suffered by this particular group of men, and that there was possibly something of value to be obtained from a comparative analysis of this sickness absence with the local meteorological conditions and atmospheric pollution. With regard to the diagnosis of chronic broncmtis, further standard&ion is greatly to be desired, as Professor HOLLAND states. These cases were all in the later stages of the disease, as I tried to imply by my, perhaps, rather abbreviated definition. The principal paper on this survey enlarges the definition somewhat to: “All the subjects considered to be suffering from chronic bronchitis had a chronic affection of the bronchi and bronchiles characterised by cough, sputum and breathlessness, with these symptoms present over all or most of the year, and were having periodic absences from work due to *J. GREGORY, AtmosphericEnvironment4, 453-468 (1970). 435
Pergamon Press 1971. Vol. 5, pp. 435136. Printed in Great Britain.
DISCUSSION THE INFLUENCE
OF CLIMATE
ON EXACERBATIONS
AND A~OSP~E~C
OF CHRONIC
POLL~ION
BRONCHITIS*
Tms interesting paper examines a topic which has concerned specialists in chronic respiratory disease for a number of years. Detailed analysis of retrospective data on sickness absence for chronic bronchitis in relation to temperature, humidity, and smoke and sulphur pollution suggests two principal conclusions: firstly, that smoke appears to be more important than sulphur dioxide in influencing exacerbations of chronic bronchitis; and secondly, that temperature may influence return to work, either by delaying recovery or because low temperature results in a lack of desire or inability to resume work. While I accept both findings as valuable hypotheses, it is however necessary to point out a number of weaknesses both in the method of analysis and in the data used. In the first place, the data is analysed solely by multiple regression analysis, and no attempt is made to eliminate the possible effect of large-scale seasonal fluctuations. Both temperature and pollution levels vary directly with the time of year, and any correlation involving these variables may simply reveal seasonal variation, which could be due to one or a number of other factors-the obvious one being liability to respiratory infection, though changes in patterns of behaviour could also be responsible. This problem has already been dealt with in some detail and a suitable method of analysis has been developed (HOLLAND et&, 1961; HOLLAND and SPICER, 1966). My second reservation about this paper concerns the prevalence and incidence rates used, which are not truly related to the population at risk. This is, of course, a problem found in all studies based on industrial sickness absence records, since the survey group differs from the general population in both age and sex, and probably also in general fitness. In addition, no attempt is made to allow for the influence of personal or other environmental factors which may well contribute to exacerbations in chronic bronchitis. It is, for example, very possible that cigarette smoking habits may have changed over the 6-yr study period. Finally, the definition of chronic bronchitis used in the study is not precisely stated. A number of studies have shown considerable variability in the use of this diagnosis and have clearly demonstrated the need to adopt a standard definition of this condition. The relationship between atmospheric pollution and chronic respiratory disease is extremely complex, as all investigators of this subject must be aware. The collection of accurate and adequate data on all the relevant factors may in some situations present insuperable problems, and some form of compromise will sometimes have to be reached. Nevertheless, I feel that in this paper the author does not appear to have fully appreciated all the difficulties involved. St. Thhomas' Hospital ~edicai School, London, S.E.1
W. S.‘. HOLLAX~
AUTHOR’S REPLY Clinical involvement with pneum~oniosis and chronic bronchitis since 1946 has made me only too aware of the complexity of the problems in assessing the various factors associated with both the morbidity and mortality of the latter disease. However, I am no statistician and anv statistical failinas must be put down to the fact that the material was extracted from old records with statistical hej;) coming late and, of necessity, no statistical preplanning. This work was part of a larger retrospective survey of clinical records (to be publ~hed in the Archives ofEnvironmentalHealrh), and it was only whilst studying these I realised that I had a complete record of all the sickness absence suffered by this particular group of men, and that there was possibly something of value to be obtained from a comparative analysis of this sickness absence with the local meteorological conditions and atmospheric pollution. With regard to the diagnosis of chronic broncmtis, further standard&ion is greatly to be desired, as Professor HOLLAND states. These cases were all in the later stages of the disease, as I tried to imply by my, perhaps, rather abbreviated definition. The principal paper on this survey enlarges the definition somewhat to: “All the subjects considered to be suffering from chronic bronchitis had a chronic affection of the bronchi and bronchiles characterised by cough, sputum and breathlessness, with these symptoms present over all or most of the year, and were having periodic absences from work due to *J. GREGORY, AtmosphericEnvironment4, 453-468 (1970). 435