Vol. 102, No. 2
AMERICAN JOURNAL OF EPIDEMIOLOGY
Printed in U.S.A.
Copyright © 1975 by The Johns Hopkins University
TUCSON EPIDEMIOLOGIC STUDY OF OBSTRUCTIVE LUNG DISEASES II: EFFECTS OF IN-MIGRATION FACTORS ON THE PREVALENCE OF OBSTRUCTIVE LUNG DISEASES' MICHAEL D. LEBOWITZ AND BENJAMIN BURROWS Lebowitz, M.D.. and B. Burrows (Arizona Medical Center. Tucson. AR 85724). Tucson epidemiologic study of obstructive lung diseases. II: Effects of in-migration factors on the prevalence of obstructive lung diseases. Am J Epidemiol 102:153-163, 1975.—The effects of in-migration factors on respiratory symptoms, chronic health problems, and lung function were examined in the stratified Tucson population as part of a longitudinal epidemiologic study of obstructive lung diseases. Migration to the area specifically for health reasons explained part of the high prevalences of disease found in the study. But natives still had higher rates of disease than those found generally in the United States, especially for asthma and allergic rhinitis. It was found that previous urban residence was related to the prevalence of several conditions, even when controlling for age, sex, and smoking habits. However, the trends were not always clear and the differences were not great enough to explain the Tucson population's much higher rates of these conditions than reported nationally or in similar studies elsewhere. lung diseases, obstructive; migration; smoking; urbanization INTRODUCTION
In a previous report (1), it was noted that the prevalence of obstructive lung diseases in Tucson, Arizona, was about twice that for the country as a whole. This is presumed to result, at least in part, from selective in-migration of subjects with respiratory disorders. It could also be influenced by large numbers of in-migrants from highly urbanized environments since exposure to such environments early in life might predispose to later development of respiratory disease. These in-migration factors could be of major importance in Tucson since almost 90 per cent of adults have moved here from other regions. Received for publication July 1, 1974, and in final form April 14, 1975. Abbreviation: COLD, chronic obstructive lung disease. 1 From the Arizona Medical Center, College of Medicine, Division of Respiratory Sciences, Tucson, Arizona 85724. This work was supported by National Heart and Lung Institute, S.C.O.R. grant No. HL14136.
Many studies have shown that the prevalence of obstructive lung diseases is related to urban residence and migration factors (2-11). Occupation, exposure to infection, smoking habits, cultural and social factors, may play a part in this effect (4). The excess mortality from chronic bronchitis in urban areas, which may be twice that in rural areas (11), is assumed to result, at least in part, from greater exposure to air pollutants. The present report examines the following questions: a) To what extent does in-migration of subjects for health reasons explain Tucson's high prevalences of respiratory diseases? b) Is there a relationship between previous urban residence and current respiratory disease among Tucson residents? c) Can Tucson's high rates be explained completely by in-migration factors, or may the incidence of disease be high in Tucson residents as a result of other conditions (such as local environmental conditions or in-breeding of a susceptible population)?
153
154
LEBOWITZ AND BURROWS METHODS
The Tucson epidemiologic study has been described in detail in part I of this report (1). Briefly, it is a stratified cluster sample of Anglo-white households in the Tucson area. Approximately 3800 individuals are enrolled in this longitudinal study, and the data described in this paper are taken from the first year of the study. Subjects were asked specifically if they had moved to southern Arizona from elsewhere, and if so, from what type of place, and for how long they had lived in southern Arizona. Standard respiratory history and smoking questions were asked, as were demographic questions. Family history information including moves for health reasons was elicited. If a family member moved for health reasons, the specific reason was indicated. The data were analyzed utilizing standard cross tabular routines including x2 tests, i-test, and other nonparametric tests, and by use of multivariate analysis such as regression analysis. The replication of analyses performed by others (2-5) has also been undertaken.
zona from elsewhere. In table i, the migration statistics are provided, indicating the proportion moving here by age, and the size of community from which the individuals came. The total number moving to southern Arizona in the sample was 82.8 per cent, of whom 8.9 per cent came from a very large city (1 million or more), 22.1 per cent from a large city (100,000 to 1 million), 11.6 per cent from a suburb of a metropolitan area, 24.6 per cent from a small city (5000 to 100,000), 8.2 per cent from a town (under 5000), and 7.3 per cent from a rural area; only 17.2 per cent of the study population were natives of southern Arizona. The percentage of persons who had moved to Arizona increased with age. The mean time lived in Arizona, of course, also increased with age.
Health-related migration There were 186 subjects (5.3 per cent) who moved to southern Arizona because of specific respiratory troubles (emphysema, chronic bronchitis, asthma, or allergies); an additional 817 (23.4 per cent) moved here for other health reasons (these groups will be termed "respiratory in-migrants" RESULTS and "health migrants," respectively) and a Almost 90 per cent of the adult popula- large group moved for nonhealth reasons tion in this study moved to southern Ari- (53.9 per cent). The group moving here for TABLE 1
Mean years in southern Arizona by age, if moved, and type of area in which most of life was spent* Total persons
In-migrants Very large city Large city Suburb Small city Town Rural Natives Total % of native population
No. of persons and mean years in southern Arizona, by age
15-29
Age 1 million: large city = 100,000-1 million; small city = 5,000-100,000; town = .10; s, significant (x*, P < 05).
157
OBSTRUCTIVE LUNG DISEASES IN TUCSON TABLE 4
The age-specific prevalence rates {per 100) of reported diagnoses in adult respondents by whether the family {excluding the respondent) moved to southern Arizona for health reasons Age and family reason for moving 15-29 Respiratory Other health Non-health 30-44 Respiratory Other health Non-health 45-59 Respiratory Other health Non-health 60-74 Respiratory Other health Non-health
Physician-diagnosed
Present heart trouble
78 83 520
2.4 1.7
681
nst
1.5 ns
25.6 24.1 17.9 ns
27 36 271 334
3.7 2.8 2.2 ns
3.7 5.6 4.8 ns
37.0 16.7 21.0 ns
29 43 292 364
3.4 9.3 7.9 ns
10.3 11.6 14.7 ns
27 46 310
22.2 17.4 16.8 ns 11.1 27.3 30.8 p = .05
"383~ 75+ Respiratory Other health Non-health
PrBscnt high blood pressure
No. of persons
9 22 104 135
ABE*
Present emphysema
Present chronic bronchitis
Present asthma
Pneumonia history
Present allergy
1.2 ns
10.3 4.8 4.6 p = .035
14.1 14.5 15.4 ns
47.4 43.4 41.9 ns
14.8
11.1
1.1 ns
2.2 p = .03
2.2
25.9 30.6 22.1 ns
63.0 36.1 49.8 ns
17.2 16.3 20.1 ns
3.4 2.3 4.8 ns
3.4
2.3 1.4 ns
20.7 20.9 29.4
44.8 55.8 41.3 ns
29.6 15.2 21.3 ns
7.4 21.7 19.7 ns
8.7 5.8 ns
8.7 6.1 ns
33.9 9.1 21.2 ns
11.1 22.7 17.3 ns
13.6 1.9 ns
9.1 8.7 p = .02
1.3
2.6
4.4 ns
ns
ns
44.4 37.0 24.8 p = .03
25.9 39.1 35.8 ns
4.5 1.9 ns
11.1 54.5 34.6 p = .056
22.2 18.2 30.8
3.7 6.5 2.9
ns
* ABE, asthma, any kind of bronchial trouble, or emphysema. More people responded affirmatively to the more general question of "any kind of bronchial trouble" than to the questions on specific disorders. t ns, statistically not significant (x ! , p > .10).
ing to whether or not the family moved for health reasons. Those whose families, but not themselves, moved here for respiratory reasons, had higher prevalence rates than % of cases subjects whose families did not move for by migration status health reasons, but the difference between Onset Total RespiOther Nonthem and non-health migrants is signifiratory health health cant only in a few cases (table 4). In some COLD n = 126 n = 129 n = 204 n = 459 cases, those whose families moved here Since 17.5 35.7 41.0 33.1 move for other health reasons had significantly Before 82.5 59.0 64.3 66.9 higher prevalence rates than non-health move Asthma n = 110 n = 76 n = 141 n = 327 migrants. Thus, the tendency for family 6.4 Since 32.9 37.6 26.0 members of respiratory in-migrants to move Before 93.6 67.1 62.4 74.0 have more respiratory problems is neither move strong nor consistent. * Differences statistically significant (x*, P < .0001). Given the differences in COLD and asthma prevalence rates between the difhad no personal or family health problem ferent migration status groups, the age of prompting their family's original move to onset of asthma and the age of onset of Arizona. The age-specific prevalence rates COLD by age cohorts were examined for of reported disease were compared accord- these different groups. As seen in table 5, TABLE 5
Percentage of cases of COLD and asthma cases by whether onset was since or before moving, and by migration status*
158
LEBOWITZ AND BURROWS
most of the onsets of asthma and COLD occur prior to in-migration, although the differences in when they occur are quite great between the different migrant groups. As expected, almost all COLD and asthma began before moving to southern Arizona for respiratory reasons while onethird of those who moved here for other health reasons or non-health reasons had onsets since the move. Furthermore, as seen in table 6, the age at onset of COLD by age cohort is quite different within the different migration groups. Considering both the age at onset of COLD and its onset in relationship to migration for the different migration groups, the age at onset for any given
cohort differs among the migration groups and also depends on the onset of disease in relation to migration. Social aspects of migration It is apparent that migration into southern Arizona, especially for respiratory and other health reasons is a major factor affecting the prevalence of disease in the Tucson area. It is, therefore, necessary to examine the relation of migration status to other important variables, as well as to examine the influence of migration status on the prevalence of disease when these variables are controlled. Many social variables show a significant relationship to respiratory findings in this population. They
TABLE 6
Percentage of cases of COLD* by age at onset and by migration status Age cohorts and migration status
No. of cases
% of cases by age at onset Age
AMERICAN JOURNAL OF EPIDEMIOLOGY
Printed in U.S.A.
Copyright © 1975 by The Johns Hopkins University
TUCSON EPIDEMIOLOGIC STUDY OF OBSTRUCTIVE LUNG DISEASES II: EFFECTS OF IN-MIGRATION FACTORS ON THE PREVALENCE OF OBSTRUCTIVE LUNG DISEASES' MICHAEL D. LEBOWITZ AND BENJAMIN BURROWS Lebowitz, M.D.. and B. Burrows (Arizona Medical Center. Tucson. AR 85724). Tucson epidemiologic study of obstructive lung diseases. II: Effects of in-migration factors on the prevalence of obstructive lung diseases. Am J Epidemiol 102:153-163, 1975.—The effects of in-migration factors on respiratory symptoms, chronic health problems, and lung function were examined in the stratified Tucson population as part of a longitudinal epidemiologic study of obstructive lung diseases. Migration to the area specifically for health reasons explained part of the high prevalences of disease found in the study. But natives still had higher rates of disease than those found generally in the United States, especially for asthma and allergic rhinitis. It was found that previous urban residence was related to the prevalence of several conditions, even when controlling for age, sex, and smoking habits. However, the trends were not always clear and the differences were not great enough to explain the Tucson population's much higher rates of these conditions than reported nationally or in similar studies elsewhere. lung diseases, obstructive; migration; smoking; urbanization INTRODUCTION
In a previous report (1), it was noted that the prevalence of obstructive lung diseases in Tucson, Arizona, was about twice that for the country as a whole. This is presumed to result, at least in part, from selective in-migration of subjects with respiratory disorders. It could also be influenced by large numbers of in-migrants from highly urbanized environments since exposure to such environments early in life might predispose to later development of respiratory disease. These in-migration factors could be of major importance in Tucson since almost 90 per cent of adults have moved here from other regions. Received for publication July 1, 1974, and in final form April 14, 1975. Abbreviation: COLD, chronic obstructive lung disease. 1 From the Arizona Medical Center, College of Medicine, Division of Respiratory Sciences, Tucson, Arizona 85724. This work was supported by National Heart and Lung Institute, S.C.O.R. grant No. HL14136.
Many studies have shown that the prevalence of obstructive lung diseases is related to urban residence and migration factors (2-11). Occupation, exposure to infection, smoking habits, cultural and social factors, may play a part in this effect (4). The excess mortality from chronic bronchitis in urban areas, which may be twice that in rural areas (11), is assumed to result, at least in part, from greater exposure to air pollutants. The present report examines the following questions: a) To what extent does in-migration of subjects for health reasons explain Tucson's high prevalences of respiratory diseases? b) Is there a relationship between previous urban residence and current respiratory disease among Tucson residents? c) Can Tucson's high rates be explained completely by in-migration factors, or may the incidence of disease be high in Tucson residents as a result of other conditions (such as local environmental conditions or in-breeding of a susceptible population)?
153
154
LEBOWITZ AND BURROWS METHODS
The Tucson epidemiologic study has been described in detail in part I of this report (1). Briefly, it is a stratified cluster sample of Anglo-white households in the Tucson area. Approximately 3800 individuals are enrolled in this longitudinal study, and the data described in this paper are taken from the first year of the study. Subjects were asked specifically if they had moved to southern Arizona from elsewhere, and if so, from what type of place, and for how long they had lived in southern Arizona. Standard respiratory history and smoking questions were asked, as were demographic questions. Family history information including moves for health reasons was elicited. If a family member moved for health reasons, the specific reason was indicated. The data were analyzed utilizing standard cross tabular routines including x2 tests, i-test, and other nonparametric tests, and by use of multivariate analysis such as regression analysis. The replication of analyses performed by others (2-5) has also been undertaken.
zona from elsewhere. In table i, the migration statistics are provided, indicating the proportion moving here by age, and the size of community from which the individuals came. The total number moving to southern Arizona in the sample was 82.8 per cent, of whom 8.9 per cent came from a very large city (1 million or more), 22.1 per cent from a large city (100,000 to 1 million), 11.6 per cent from a suburb of a metropolitan area, 24.6 per cent from a small city (5000 to 100,000), 8.2 per cent from a town (under 5000), and 7.3 per cent from a rural area; only 17.2 per cent of the study population were natives of southern Arizona. The percentage of persons who had moved to Arizona increased with age. The mean time lived in Arizona, of course, also increased with age.
Health-related migration There were 186 subjects (5.3 per cent) who moved to southern Arizona because of specific respiratory troubles (emphysema, chronic bronchitis, asthma, or allergies); an additional 817 (23.4 per cent) moved here for other health reasons (these groups will be termed "respiratory in-migrants" RESULTS and "health migrants," respectively) and a Almost 90 per cent of the adult popula- large group moved for nonhealth reasons tion in this study moved to southern Ari- (53.9 per cent). The group moving here for TABLE 1
Mean years in southern Arizona by age, if moved, and type of area in which most of life was spent* Total persons
In-migrants Very large city Large city Suburb Small city Town Rural Natives Total % of native population
No. of persons and mean years in southern Arizona, by age
15-29
Age 1 million: large city = 100,000-1 million; small city = 5,000-100,000; town = .10; s, significant (x*, P < 05).
157
OBSTRUCTIVE LUNG DISEASES IN TUCSON TABLE 4
The age-specific prevalence rates {per 100) of reported diagnoses in adult respondents by whether the family {excluding the respondent) moved to southern Arizona for health reasons Age and family reason for moving 15-29 Respiratory Other health Non-health 30-44 Respiratory Other health Non-health 45-59 Respiratory Other health Non-health 60-74 Respiratory Other health Non-health
Physician-diagnosed
Present heart trouble
78 83 520
2.4 1.7
681
nst
1.5 ns
25.6 24.1 17.9 ns
27 36 271 334
3.7 2.8 2.2 ns
3.7 5.6 4.8 ns
37.0 16.7 21.0 ns
29 43 292 364
3.4 9.3 7.9 ns
10.3 11.6 14.7 ns
27 46 310
22.2 17.4 16.8 ns 11.1 27.3 30.8 p = .05
"383~ 75+ Respiratory Other health Non-health
PrBscnt high blood pressure
No. of persons
9 22 104 135
ABE*
Present emphysema
Present chronic bronchitis
Present asthma
Pneumonia history
Present allergy
1.2 ns
10.3 4.8 4.6 p = .035
14.1 14.5 15.4 ns
47.4 43.4 41.9 ns
14.8
11.1
1.1 ns
2.2 p = .03
2.2
25.9 30.6 22.1 ns
63.0 36.1 49.8 ns
17.2 16.3 20.1 ns
3.4 2.3 4.8 ns
3.4
2.3 1.4 ns
20.7 20.9 29.4
44.8 55.8 41.3 ns
29.6 15.2 21.3 ns
7.4 21.7 19.7 ns
8.7 5.8 ns
8.7 6.1 ns
33.9 9.1 21.2 ns
11.1 22.7 17.3 ns
13.6 1.9 ns
9.1 8.7 p = .02
1.3
2.6
4.4 ns
ns
ns
44.4 37.0 24.8 p = .03
25.9 39.1 35.8 ns
4.5 1.9 ns
11.1 54.5 34.6 p = .056
22.2 18.2 30.8
3.7 6.5 2.9
ns
* ABE, asthma, any kind of bronchial trouble, or emphysema. More people responded affirmatively to the more general question of "any kind of bronchial trouble" than to the questions on specific disorders. t ns, statistically not significant (x ! , p > .10).
ing to whether or not the family moved for health reasons. Those whose families, but not themselves, moved here for respiratory reasons, had higher prevalence rates than % of cases subjects whose families did not move for by migration status health reasons, but the difference between Onset Total RespiOther Nonthem and non-health migrants is signifiratory health health cant only in a few cases (table 4). In some COLD n = 126 n = 129 n = 204 n = 459 cases, those whose families moved here Since 17.5 35.7 41.0 33.1 move for other health reasons had significantly Before 82.5 59.0 64.3 66.9 higher prevalence rates than non-health move Asthma n = 110 n = 76 n = 141 n = 327 migrants. Thus, the tendency for family 6.4 Since 32.9 37.6 26.0 members of respiratory in-migrants to move Before 93.6 67.1 62.4 74.0 have more respiratory problems is neither move strong nor consistent. * Differences statistically significant (x*, P < .0001). Given the differences in COLD and asthma prevalence rates between the difhad no personal or family health problem ferent migration status groups, the age of prompting their family's original move to onset of asthma and the age of onset of Arizona. The age-specific prevalence rates COLD by age cohorts were examined for of reported disease were compared accord- these different groups. As seen in table 5, TABLE 5
Percentage of cases of COLD and asthma cases by whether onset was since or before moving, and by migration status*
158
LEBOWITZ AND BURROWS
most of the onsets of asthma and COLD occur prior to in-migration, although the differences in when they occur are quite great between the different migrant groups. As expected, almost all COLD and asthma began before moving to southern Arizona for respiratory reasons while onethird of those who moved here for other health reasons or non-health reasons had onsets since the move. Furthermore, as seen in table 6, the age at onset of COLD by age cohort is quite different within the different migration groups. Considering both the age at onset of COLD and its onset in relationship to migration for the different migration groups, the age at onset for any given
cohort differs among the migration groups and also depends on the onset of disease in relation to migration. Social aspects of migration It is apparent that migration into southern Arizona, especially for respiratory and other health reasons is a major factor affecting the prevalence of disease in the Tucson area. It is, therefore, necessary to examine the relation of migration status to other important variables, as well as to examine the influence of migration status on the prevalence of disease when these variables are controlled. Many social variables show a significant relationship to respiratory findings in this population. They
TABLE 6
Percentage of cases of COLD* by age at onset and by migration status Age cohorts and migration status
No. of cases
% of cases by age at onset Age
