AN ANGLO-AMERICAN COMPARISON OF THE PREVALENCE OF BRONCHITIS

Systematic review with meta-analysis of the epidemiological evidence relating smoking to COPD, chronic bronchitis and emphysema

BACKGROUND

Smoking is a known cause of the outcomes COPD, chronic bronchitis (CB) and emphysema, but no previous systematic review exists. We summarize evidence for various smoking indices.

METHODS

Based on MEDLINE searches and other sources we obtained papers published to 2006 describing epidemiological studies relating incidence or prevalence of these outcomes to smoking. Studies in children or adolescents, or in populations at high respiratory disease risk or with co-existing diseases were excluded. Study-specific data were extracted on design, exposures and outcomes considered, and confounder adjustment. For each outcome RRs/ORs and 95% CIs were extracted for ever, current and ex smoking and various dose response indices, and meta-analyses and meta-regressions conducted to determine how relationships were modified by various study and RR characteristics.

RESULTS

Of 218 studies identified, 133 provide data for COPD, 101 for CB and 28 for emphysema. RR estimates are markedly heterogeneous. Based on random-effects meta-analyses of most-adjusted RR/ORs, estimates are elevated for ever smoking (COPD 2.89, CI 2.63-3.17, n = 129 RRs; CB 2.69, 2.50-2.90, n = 114; emphysema 4.51, 3.38-6.02, n = 28), current smoking (COPD 3.51, 3.08-3.99; CB 3.41, 3.13-3.72; emphysema 4.87, 2.83-8.41) and ex smoking (COPD 2.35, 2.11-2.63; CB 1.63, 1.50-1.78; emphysema 3.52, 2.51-4.94). For COPD, RRs are higher for males, for studies conducted in North America, for cigarette smoking rather than any product smoking, and where the unexposed base is never smoking any product, and are markedly lower when asthma is included in the COPD definition. Variations by sex, continent, smoking product and unexposed group are in the same direction for CB, but less clearly demonstrated. For all outcomes RRs are higher when based on mortality, and for COPD are markedly lower when based on lung function. For all outcomes, risk increases with amount smoked and pack-years. Limited data show risk decreases with increasing starting age for COPD and CB and with increasing quitting duration for COPD. No clear relationship is seen with duration of smoking.

CONCLUSIONS

The results confirm and quantify the causal relationships with smoking.

Respiratory symptoms as predictors of 27 year mortality in a representative sample of British adults

OBJECTIVE

To examine associations between reported respiratory symptoms (as elicited by questionnaire) and subsequent mortality.

DESIGN

Prospective cohort study.

SETTING

92 General practices in Great Britain.

PARTICIPANTS

A nationally representative sample of 1532 British men and women aged between 40 and 64.

MAIN OUTCOME MEASURES

Mortality from all causes, cardiovascular disease, lung cancer, and chronic bronchitis.

RESULTS

Subjects were interviewed in 1958 regarding various respiratory symptoms (including cough, phlegm, breathlessness, and wheeze) by using a questionnaire which formed the basis of the Medical Research Council's questionnaire on respiratory symptoms. By the end of 1985, 889 deaths had been reported, including 51 in men due to chronic bronchitis. After adjustment for differences in age and smoking habits death rates from chronic bronchitis in men who reported symptoms were greater than those in men who did not for each of the symptoms examined. The adjusted mortality ratios were 3.4 (95% confidence interval 1.8 to 6.5) for morning cough, 3.7 (2.0 to 6.9) for morning phlegm, 6.4 (3.0 to 13.8) for breathlessness when walking on the level, and 10.5 (4.4 to 24.6) for wheeze most days or nights. Mortality ratios were also significantly raised for four episodic symptoms not usually included in more recent respiratory symptom questionnaires--namely, occasional wheeze (mortality ratio 6.0; 95% confidence interval, 2.4 to 15.1), weather affects chest (5.7; 3.1 to 10.3), breathing different in summer (4.9; 2.8 to 8.6), and cold usually goes to chest (3.7; 2.0 to 6.8). The excess mortality associated with these symptoms remained significant after further adjustment for breathlessness or phlegm. Ratios for all cause mortality in men and women were also significantly raised for most respiratory symptoms, death rates being some 20-50% higher in people reporting symptoms after adjustment for age, sex, and smoking. Breathlessness was the only symptom significantly associated with excess mortality from cardiovascular disease (mortality ratio 1.4 (95% confidence interval 1.0 to 1.9) for breathlessness when walking on the level). Ratios were generally around unity and not significant for mortality due to lung cancer.

CONCLUSIONS

The results suggest that episodic symptoms, which often do not appear in standard respiratory questionnaires, predict subsequent mortality from chronic obstructive airways disease. This supports the hypothesis that reversible airflow obstruction may be a precursor of progressive and irreversible decline in ventilatory function.

COPD prevalence in nonsmokers in high and low photochemical air pollution areas

The prevalence of respiratory symptoms, as ascertained by questionnaire, was evaluated in 6,666 nonsmokers who had lived for at least 11 years in either a high photochemical pollution area (4,379 individuals) or a low photochemical pollution area (2,287 individuals). Of these, 5,178 had never smoked, and none was currently smoking. The risk estimate for "definite" COPD, as defined in this study, was 15 percent higher in the high pollution area (p = 0.03), after adjusting for sex, age, race, education, occupational exposure, and past smoking history. Past smokers had a risk estimate 22 percent higher than never smokers (p = 0.01). Multivariate analysis showed a significant effect of air pollution on the prevalence of "definite" COPD which univariate analysis failed to demonstrate.

A comparison of three systems of classifying presenting problems in general practice

Three internationally recognized systems have been devised for classifying presenting problems in general practice. They are: the Royal College of General Practitioners' (1963) classification, the US Ambulatory Medical Care Classification of Symptoms (NAMCS), and the World Organization of Colleges and Academies of General Practice/Family Medicine (WONCA, 1976) classification which is known as An International Classification of Health Problems of Primary Care (ICHPPC).These three systems were compared in over 8,000 consultations conducted by 81 randomly selected British general practitioners in Nottinghamshire.For all ages of patient, the NAMCS, which has only 197 categories, was the most specific, and the least specific was the classification of the Royal College of General Practitioners.

Review of the health effects of sulfur oxides

The pollution in the air is a complex mixture of chemical substances of varying toxicity of which the sulfur oxides are a principal component. Those components which pose the primary hazards to human health have not yet been fully identified, nor have their respective contributions to human disease been fully determined. Efficient and effective control strategies are dependent upon the identification and understanding of these toxic components. Ultimately, the goal of standard-setting should be the development of composite pollution indices rather than control of individual pollutants. Concentrations of SO(2) in the ambient air twice the current standards are associated with adverse health effects. A considerable body of evidence suggests that there may be discernible human health effects from exposure to concentrations approximating the current standards. There is therefore no basis for relaxation of the present standards for sulfur oxides at this time. Since the scientific basis for this judgment is incomplete, further scientific information will be required either to validate the present standards or to justify alteration of these standards.

Chronic bronchitis: method of cigarette smoking

Male volunteers for mass radiography examination, aged 40 or more, were questioned about their sputum production, smoking habits, and, when applicable, their method of smoking cigarettes.Of 5,438 cigarette smokers 460 (8.4%) smoked their cigarettes without removing the cigarette from the mouth between puffs ("drooping" cigarette smokers) whereas the rest smoked in the normal manner.Persons who admitted to producing sputum from their chests on most days of the year or on most days for at least three months of the year for a minimum of two years were classified as chronic bronchitics in the absence of other causative disease.The rate of chronic bronchitis among the "drooping" cigarette smokers (41.5%) was considerably greater than that among those smoking cigarettes in the normal manner (33.6%). The same pattern was maintained when age and cigarette consumption were standardized, though "drooping" cigarette smokers had a slight bias towards plain as distinct from filter cigarettes and towards a lower social class this was not sufficient to account for the excess of chronic bronchitis among those using this method of smoking.

Some unresolved problems in chronic respiratory disease

In this lecture the position concerning some of the present-day problems in the field of chronic respiratory disease have been reviewed. First among these —the differentiation of the 3 components chronic bronchitis, emphysema and asthma—is seen to have been only partly accomplished by accepted definitions. The place of emphysema as a major accompaniment of chronic bronchitis is particularly baffling during life. The controversy regarding the reversibility of airways obstruction is held to affect the definition of asthma and should be a stimulus to renewed efforts to clarify the situation. In both emphysema and asthma attention ought to be directed towards epidemiological studies in order to elucidate aetiological factors.

The second major problem—that of the earliest stages of chronic bronchitis— is important in the recognition of the role of causative factors known to be important at a later stage. Air pollution and infection thus occupy a tentative causative role even before cigarette smoking becomes effective in eliciting mucus production by the airways. The role of genetic factors has been highlighted with the advent of knowledge concerning the serum α 1-antitrypsin globulin. Detailed clinical and epidemiological studies are now required.

The third problem is a prognostic one. In such long-lasting complaints as those under consideration, diagnosis at an early stage might surely lead to attempts to prevent progression. Here the mystery of the variability of the natural history of different individuals is the problem and airways obstruction is seen to be a major determinant of ventilatory/perfusion relationships. These in turn are prognostically related not only to respiratory failure but to pulmonary hypertension and cor pulmonale.

Chronic respiratory disease in the elderly. A population study

A study has been made of chronic respiratory disease among 83 men and 217 women aged 65 and over, randomly chosen from those living in their own homes. Twenty-six per cent of the men and 13% of the women had chronic bronchitis. The prevalence of chronic bronchitis was related to current cigarette smoking in both sexes, and to socio-economic status in men. Chronic bronchitis was a contributory cause of disabling dyspnoea and recurrent chest illness in half of the subjects with these symptoms.

Significant radiological evidence of tuberculosis was found in 9% of men and in 4% of women, asthma in 2% of women, industrial lung disease in 4% of men, and bronchogenic carcinoma in three subjects.

Phlegm and filters

Male mass radiography volunteers aged 40 or more were questioned about their sputum production and cigarette consumption in relation to type (filter or plain) smoked. Of 10,414 volunteers, 3,045 smoked filter cigarettes and 2,393 smoked plain cigarettes. The rate of persistent daily sputum of filter smokers (31.9%) was significantly lower than that of plain cigarette smokers (37.2%). A similar pattern was maintained when age and cigarette consumption were standardized. These figures are thought to understate the less injurious nature of filter cigarettes, since more than half of the filter smokers with persistent sputum developed this while previously smoking plain cigarettes.Whatever the reasons for the less injurious nature of filter cigarettes, it seems that cigarette smokers unable to stop smoking might suffer less from chronic bronchitis if they changed to filter cigarettes.

Distribution of bronchial gland measurements in a Jamaican population

Measurements of the gland thickness and Reid index have been made on bronchi obtained at necropsy on 53 male and 52 female Jamaicans. The mean values for the Reid index and mucous gland thickness obtained were 0·314 and 0·192 mm. for males, and 0·302 and 0·170 mm. for females respectively. No significant increase in value was seen with age, although the data suggest this trend. The results have been compared with data published from Montreal and the same overall Gaussian distribution is seen. This supports the suggestion that the gland measurements in non-bronchitic and bronchitic subjects do not fall into two distinct groups but are part of a continuous distribution. The similarity of the two studies is also of interest as the populations are drawn from two distinct environments, one from a non-industrialized tropical island, the other from a large city in the northern hemisphere.

THE CHILLIWACK RESPIRATORY SURVEY, 1963: 3. THE PREVALENCE OF RESPIRATORY DISEASE IN A RURAL CANADIAN TOWN

The prevalence of chronic respiratory symptoms and of abnormalities in pulmonary function was determined by a survey of persons, aged 25 to 74, residing during May and June 1963 in a rural town, Chilliwack, B.C. Morning phlegm was reported by 26% of men and 13% of women. Chronic bronchitis was considered present in 21.5% of men and 11.3% of women. More serious obstructive lung disease, not related to heart disease, was found in 12.6% of men and 8.7% of women. These prevalences were higher than those found by the authors at Berlin, New Hampshire, U.S.A., in 1961. Demographic factors, such as birthplace, occupational class and measures of social stability, were not related to the prevalence of respiratory disease at Chilliwack. Some observer variation was found after analysis to be the result of non-randomization of respondents among the observers. An incidental observation was a high prevalence at Chilliwack of heart disease and hypertension under treatment.

THE CHILLIWACK RESPIRATORY SURVEY, 1963. II. AEROMETRIC STUDY

A study of the quality of the ambient air at Chilliwack, British Columbia, was conducted from May 1963 to April 1964. Measurements of dustfall, soiling, sulfation, hydrogen sulfide, oxidants and total hydrocarbons were made by a network of five sampling stations. The results of this survey indicated that Chilliwack was relatively free from any air pollution and would therefore be a suitable control for a study of the relationship between community air pollution and respiratory disease.