Epidemiology and Air Pollution (1985) / Chapter Skim
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5 THE APPLICATION OF EPIDEMIOLOGY TO SELECTED RESEARCH QUESTIONS
5 THE APPLICATION OF EPIDEMIOLOGY TO SELECTED RESEARCH QUESTIONS
Pages 165-190
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From page 165... ...
The following components are addressed: • Selection of a study method. • Selection of study populations.
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From page 166... ...
Ecologic studies are not foreseeable, because widely reported data on the incidence of these conditions are lacking. The prospective cohort method requires the study of a relatively common end point, perhaps upper respiratory infections, as opposed to more serious lower respiratory infections (such as acute bronchitis and pneumonia)
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From page 167... ...
The specific pollutants of interest in studies of respiratory infection might be nitrogen oxides, gas stove emission, passively received cigarette smoke, woodsmoke, acid aerosols, and recurrent summertime haze and ozone. If a small-cohort frequent-event approach is taken, it should be possible to use individual, rather than aggregate, monitoring data on pollutant exposure.
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From page 168... ...
CHRONIC OBSTRUCTIVE PULMONARY DISEASE "Do any current patterns of exposure to air pollutants lead to an excess risk of developing chronic obstructive pulmonary disease (COPD) or to exacerbation of existing COPD?
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From page 169... ...
The use of rapid decline of FEV1 or of other measures of pulmonary function as markers of COPD is desirable, in that rapid decline is far more common than clinically apparent disease; etiologic studies can therefore be shorter and cheaper and have satisfactory statistical power. Berry, Schlesselman, and others have shown that varying the number of subjects followed, the frequency of lung function measurement, and the length of followup makes it possible to maximize the chances of detecting an effect of a given magnitude without wasting resources on excess measurements.6 22 Table 1 shows the numbers of
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From page 170... ...
THE APPLICATION OF EPIDEMIOLOGY TO SELECTED RESEARCH QUESTIONS 170 TABLE 1 LONGITUDINAL OBSERVATIONS Number of Subjects Required in Followup Study of FEV1 in Each of Two Groups, to Detect Differences of 0.03 L/year at Significance Level of 0.05 and Power of 0.8a Length of Intervals Between Measurements CrossFollowup, 1 3 6 1 Beginning Sectional years Month Months Months Year and End Study on Only Subjects Previously Exposed for Length of Followup 1 226 429 530 530 530 4,356 2 56 95 128 153 153 1,089 3 36 50 64 78 84 484 4 32 38 45 53 59 272 5 30 33 37 42 48 174 6 29 31 33 37 42 121 7 29 30 31 34 38 89 8 28 29 30 32 36 68 9 28 29 30 31 34 54 10 28 29 29 30 33 44 a Reprinted with permission from Berry.4
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From page 171... ...
As previous discussions have pointed out, however, this consideration accounts only for random errors; in the case of cross-sectional studies of chronic respiratory disease, the nonrandom error associated with retrospective exposure assessment would be a dominant concern and would limit the types of answers that could be expected. A research strategy on the COPD question would be enhanced by prior consideration of descriptive data on COPD incidence or mortality.
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From page 172... ...
THE APPLICATION OF EPIDEMIOLOGY TO SELECTED RESEARCH QUESTIONS FIGURE 7 Chronic bronchitis mortality among white females, 1965-1971. Reprinted from U.S.
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From page 173... ...
of carefully screened subjects with chronic respiratory diseases can be followed longitudinally. In an approach very similar to that recommended for asthma or acute respiratory infection, the goal is to ascertain the determinants of the probability of exacerbation in a person over a given period.
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From page 174... ...
Such data, when combined with data on individual effects, will permit a great increase in the overall power of almost any study method, except perhaps when outdoor exposure is a poor predictor of total exposure. ASTHMA "Do any current patterns of exposure to air pollutants lead to an increased risk of developing asthma or to exacerbation of existing asthma?
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From page 175... ...
There is every reason to believe that the types of studies described in this report will soon be able to answer questions about the relationship between the frequency of asthmatic attacks and relatively minor fluctuations in exposure to specific pollutants. LUNG CANCER "Do any current patterns of exposure to air pollutants lead to an excess risk of developing lung cancer, and does this exposure interact with cigarette smoking in producing excess risk?
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From page 176... ...
Most prospective designs would fail, because of the relative infrequency of lung cancer in the general population. But the American Cancer Society is conducting its second massive prospective study of cancer in a cohort of 1.2 million persons; such an extraordinary cohort is large enough to detect small relative risks and yield actual incidence rates among the exposed groups while permitting adjustment for important confounders, such as smoking.
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From page 177... ...
EXPOSURE TO WOODSMOKE "Does current exposure to woodsmoke cause or worsen acute or chronic respiratory disease, lead to acute or chronic changes in pulmonary function, or increase the risk of lung cancer?
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From page 178... ...
The effect measurements in woodsmoke studies could include symptom frequency, frequency of respiratory infection or asthmatic attacks, transient or persistent changes in lung function, changes in lung clearance, and markers of genetic damage in somatic cells. Reporting of acute respiratory symptoms in children might be particularly productive, as indicated by a recent study in Michigan.11 The increase in the use of wood as a fuel in the United states has been relatively recent (except in some distinct populations, such as the Navajo Indians)
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From page 179... ...
EXPOSURE TO NITROGEN DIOXIDE "Does total exposure to nitrogen dioxide, from both indoor and outdoor sources, lead to or exacerbate acute or chronic respiratory diseases?
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From page 180... ...
The role of NO2 exposure in serious respiratory infections among infants has already been addressed in connection with the case-control study discussed early in this chapter.27 Transient and persistent changes in lung function and symptom frequency are also of concern. In particular, new data on the effect of specific NO2 sources on rates of lung growth in children need confirmation and expansion.
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From page 181... ...
There is a concern over the potential influence of these patterns of exposure on the risk of developing COPD. Results of long-term animal exposure studies support this possibility and a recent longitudinal study of an ozone-exposed cohort in Los Angeles pointed to decrements in pulmonary function among several age groups (unpublished manuscript, R
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From page 182... ...
EPISODIC EXPOSURE TO OZONE AND ACID AEROSOL HAZE "Does episodic exposure to ozone or acid aerosols at high concentrations lead to excess morbidity from acute and chronic respiratory diseases? " In addition to the problem of persistent exposure to ozone and acid aerosols, there is an emerging regional pattern of summertime "haze" episodes in the Northeast.
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From page 183... ...
The potential chronic effects of episodic ozone and acid aerosol will remain more difficult to study, in part because of the relatively recent appearance of the pollution pattern and because of the difficulty involved in separating persistent from episodic exposures. Again, rural areas that generally have low exposure to ozone and primary acid aerosol, except during the summer, might be preferable sites for studies.
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From page 184... ...
Cohort studies of uranium miners and other types of miners have successfully demonstrated that radon and its progeny can cause lung cancer in humans. However, the least-exposed miner group that showed a significant excess of lung cancer still had cumulative lifetime exposures at least several times higher than that likely to be experienced by residentially exposed persons.17 Cohort studies (either prospective or historical-prospective)
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From page 185... ...
Recent work in dose modeling has clarified some of the factors (including dust concentrations) involved in extrapolating radon dosage from the mine environment to the home.10 The most useful direct approach to the radon-lung cancer question is through the case-control method, so exposure measures will most often be retrospective and hence subject to considerable uncertainty.
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From page 186... ...
Histological findings in the tracheobronchial tree of uranium miners and non-miners with lung cancer. Cancer 42:483-489, 1978.
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From page 187... ...
Domestic smoke pollution and chronic bronchitis in a rural community of the Hill Region of Nepal. Thorax 39:337-339, 1984.
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From page 188... ...
Chronic bronchitis, white females, 1965-1971.
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From page 189... ...
189 Chapter 6 Conclusions and Recommendations
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