Am J Respir Crit Care Med
Internet address: www.atsjournals.org
Vol 157. pp 1864–1870, 1998
Occupation, Asthma, and Chronic Respiratory
Symptoms in a Community Sample of Older W omen
FRANCESCO FORASTIERE, JOHN BALMES, MARINA SCARINCI, and IRA B. TAGER
Division of Public Health Biology and Epidemiology, School of Public Health, University of California, Berkeley, California;
Department of Epidemiology, Lazio Regional Health Authority, Rome, Italy; and Division of Occupational and Environmental
Medicine, Department of Medicine, University of California, San Francisco, California
We evaluated the role of occupational factors on the prevalence of self-reported asthma, chronic
bronchitis, and asthma-like respiratory symptoms among women
smoking, and respiratory conditions were collected through an interviewer-administered question-
naire from 1,226 women. Lung function data from 820 subjects were used for group “validation” of
the outcome variables. Significant associations were observed between the respiratory conditions
and occupational groupings based on the longest occupation held. Artists, writers, decorators, and
photographers (odds ratio [OR]
3.1), and women in service occupations (OR
cantly increased risk of asthma. The odds of asthma-like symptoms was significantly elevated among
nurses and other nonphysician health workers (OR
2.4). Exposure to dusts, gas, vapors, fumes, or sensitizers was associated with a signifi-
cantly increased odds of asthma (OR
1.8) and with a marginally significant increased odds of
asthma-like symptoms (OR
1.4). Smoking accounted for a large proportion of asthma and asthma-
like conditions in this population (population attributable risk [PAR]
tively); employment in occupations with a high probability of exposures to dusts, gas, vapors, fumes,
or sensitizers also contributed significantly to the burden of asthma (PAR
asthma-like symptoms (PAR
7.5 to 10.2%). Forastiere F, Balmes J, Scarinci M, Tager IB. Occu-
pation, asthma, and chronic respiratory symptoms in a community sample of older women.
55 yr. Occupational history,
2.4) had a signifi-
2.9), social workers (OR
2.9), and homemak-
40.5% and 35.0%, respec-
15.1 to 20.0%) and
AM J RESPIR CRIT CARE MED 1998;157:1864–1870.
V arious substances of biologic or synthetic chemical origin
have been associated with the inception or the aggravation of
asthma among individuals who are exposed in occupational
settings (1). A lthough several disease registries and surveil-
lance systems of occupational asthma have been implemented
in various countries (2–4), the epidemiologic evidence with re-
gard to the occurrence of occupational asthma in the commu-
nity is underdeveloped (5). A limited number of studies have
estimated the burden of occupational asthma in the adult gen-
eral population (6–11). Estimates of the population attribut-
able risk (PA R) due to occupational exposure range from 2%
to 30% and are dependent on the prevalence of exposure and
the case definition employed. In the United States, few popu-
lation studies are available on the association between occu-
pational exposures and asthma or asthma-like symptoms (6,
12); and no study specifically has evaluated the occurrence of
occupational asthma among women.
In a community study of elderly women in Northern Cali-
fornia, individual information on respiratory health, smoking
habits, and occupation had been collected as a part of an on-
going longitudinal project of the effects of aging on physical
functioning (13). We used data from the baseline evaluation to
evaluate the role of smoking and of occupational factors on
the prevalence of self-reported asthma, chronic bronchitis,
and asthma-like respiratory symptoms and to estimate the
asthma-related risks attributable to smoking and to occupa-
tion in this population.
The data presented were obtained as part of the baseline evaluation
of subjects who enrolled in the Study of Physical Performance and
A ge-Related Changes in Sonomans (SPPA RCS). SPPA RCS is a com-
munity-based, longitudinal study of physical activity and fitness in
55 yr of age who live in the city and environs of Sonoma,
California (13). The dominant industries in the community are farm-
ing (wine grapes, dairy cattle) and tourism; there is no heavy industry.
A community-based census identified 3,057 age-eligible individuals of
whom 2,092 (68.4%) agreed to participate in the study and were en-
rolled between May 1993 and December 1994. Of these, there were
1,246 females who are the subjects for this report. The age distribution
of these subjects was similar to that of the 1990 census data for per-
55 who resided in the study community (13). Protocols were
approved by the Committee for the Protection of Human Subjects at
the University of California, Berkeley and the Committee on Human
Research at the University of California, San Francisco.
Supported by Grant RO1-AG09389 from the National Institute on Aging.
Correspondence and requests for reprints should be addressed to Ira Tager,
M.D., 140 Warren Hall, University of California, Berkeley, Berkeley, CA 94720-
Received in original form December 17, 1997 and in revised form February 19, 1998)
Forastiere, Balmes, Scarinci, et al. : Asthma and Occupation among Women
A s part of the initial evaluation, an interviewer-administered ques-
tionnaire was completed that contained detailed information on occu-
pational history, respiratory symptoms and illnesses, cigarette smok-
ing history, general medical conditions, and functional capacity. The
occupational history included: (
1 ) job title of current or last job; (
job title during most of subject’s working life; (
formed and duration of employment for #1 and #2; and (
or status as “currently unemployed.” Respiratory symp-
tom and illness questions were those of the A TS
Diseases (DLD), National Heart, Lung, and Blood Institute question-
naire (14), which were supplemented by detailed questions on asthma
history (e.g., age of onset, duration, medications, hospitalization, precipi-
tating factors) and wheezing. Complete questionnaire data were avail-
able for 1,226 (98.4%) of the women who enrolled in the study (differ-
ence due to subjects who could not complete the questionnaire or for
whom a proxy interview was obtained).
Subjects performed maximal expiratory maneuvers in the study
laboratory in accordance with A merican Thoracic Society criteria (15)
in the seated position with nose clip on a dry, rolling seal spirometer
linked to a computer (Plus System; Warren E. Collins, Braintree, MA ).
Calibration was performed daily with a 3-L syringe. Data were ana-
lyzed for subjects with at least two acceptable time–volume tracings
for which forced expiratory volumes in one second (FEV
within 10%. A cceptable data were available for 820 (66.9%) women.
3 ) specific work per-
4 ) reasons for
Division of Lung
On the basis of the respiratory questionnaire, three mutually exclusive
outcome categories were defined as follows:
or more) and wheezing symptoms during the past 12 mo (65 sub-
emphysema: report of a physician diagnosis of
emphysema during the past 12 mo (90 subjects).
Asthma-like symptoms : report of shortness of breath with wheeze
or chronic wheeze during the past 12 mo in the absence of a physi-
cian diagnosis of asthma or chronic bronchitis/emphysema (175 sub-
: report of a physician diagnosis of asthma (at age 18
A ll women (68 subjects) with a history of inactive respiratory dis-
orders (report of a physician diagnosis but no symptoms in the past 12
mo) and 14 subjects with childhood asthma (report of a physician di-
agnosis of asthma before the age of 18) were not included in the above
classification. The reference group was composed of 814 women who
reported that they never had any of the above respiratory conditions.
Smoking . Smoking habit was categorized into four classes: never
smokers, quitters of 10 yr or more, quitters in the previous 10 yr, and
current smokers. This classification was based on an analysis of the
distribution of lifetime cigarette smoking and forced expiratory vol-
umes, which demonstrated that subjects who quit within 10 yr of inter-
view had FEV
that were more like those of subjects who were cur-
rent smokers than those of other former smokers (data not shown).
Occupational history. The last and the longest occupation were ini-
tially coded with codes used by the 1990 U.S. Census (16). Subse-
quently, the codes for the longest occupation were grouped into 13
major occupational groups. The last and longest occupations were
identical for 81.5% of subjects (934 of 1,144). The grouping was done
without regard to the health status of the women. We tried to follow
the classification scheme of the SWORD projects in the United King-
dom (17) which has been used in two studies on the risk of asthma due
to occupation (8, 11). However, our categorization had to consider
differences between the U.S. Census and the British codes, as well as
the fact that, for several categories of the SWORD classification (e.g.,
woodworkers, welders, painters, construction workers), there were few
or no subjects in our population, given the predominance of males in
such occupations. We combined women in executive and managerial
occupations (codes: 1–89 in the U.S. Census rubric) and those in ad-
ministrative occupations (codes: 303–309) into a single category to
serve as referents in the evaluation of the association between differ-
ent occupations and respiratory conditions.
A ll job descriptions in the individual occupational histories were
reviewed blindly with regard to health status by two of us with experi-
ence in occupational medicine (F.F., M.S.). Each subject was classified
as potentially exposed or unexposed to dust, gas, vapors, fumes, or
sensitizers (DGV FS) in the workplace (first pass by F.F.). The assign-
ment to the exposed or unexposed category was based on the existing
knowledge about the factors associated with occupational asthma (1,
18), as well as on the prevalence data from the National Occupational
Exposure Survey (19). Based on the results of the first pass, a stan-
dardized assignment protocol was established. A second, complete,
blind review was undertaken by F.F.; and the assignments were made
with the standardized assignment protocol. Finally, a third, blind, in-
dependent review of the coding was undertaken by M.S. Coding dis-
agreements between M.S. and F.F. were then reconciled by mutual
agreement. Duration of exposure to dusts, gas, vapors
tizers was also recorded.
fumes, or sensi-
Multinomial logistic regression (logistic regression that permits the
outcome to take on more than two levels; mlogit of STA TA ) was
used to calculate odds ratios (OR) and 95% confidence intervals (CI)
for the association between adult asthma, chronic bronchitis, and
asthma-like symptoms with smoking and occupation. In the logistic
model, the reference group was the 814 females without any of the
respiratory conditions and symptoms of interest. In the evaluation of
the association between the three outcome variables and the occupa-
tional groups (reference group
executives, managers, administra-
tors), adjustment was made for age and smoking (reference group
never smoked). PA R of asthma and asthma-like symptoms due to
smoking and to occupation were estimated (21).
A djustment of the lung function measures was accomplished by
linear regression of the specific lung function measure on mean-cen-
DESCRIPTIVE CHARACTERISTICS OF WOMEN ENROLLED* IN STUDY
OF PHYSICAL PERFORMANCE AND AGE-RELATED CHANGES IN
SONOMANS PROJECT (SPPARCS) SONOMA, CA, 1994
VariableNumber (% of 1,226)
Inactive respiratory disorder
* 1,226 (98.4%) of the 1,246 female subjects who actually enrolled were included.
Asthma-like symptoms include shortness of breath with wheeze and chronic wheeze.
AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINEVOL 157 1998
tered age, height, dummy variable for smoking, and dummy variables
for the respiratory conditions.
Table 1 shows the selected characteristics of the women in the
population studied. Most women were white with a relatively
high educational level (62% had 13 or more years of education).
The mean age (
SD) was 70.3
70% were retired. A total of 49% were never-smokers, and 9%
were current smokers. Subjects with any of the chronic respi-
ratory conditions (39 asthmatics, 59 subjects with chronic bron-
chitis, and 115 individuals with asthma-like symptoms for whom
a lung function test was available) had significantly lower FV C,
, and FEF
values than women in the refer-
ence category (557 subjects) after adjustment for age, height,
and smoking habit in multiple linear regression (Table 2).
Women with adult asthma had the lowest lung function values.
OR and 95% CI for the association between smoking and
respiratory conditions are presented in Table 3. Former smok-
ers had an increased odds of self-reported, doctor-diagnosed
asthma, chronic bronchitis, and self-reported asthma-like symp-
toms; OR ranged from 1.4 to 4.7. There was a strong and sig-
nificant association between current smoking and both chronic
6.4) and asthma-like symptoms (OR
whereas the association between current smoking and asthma
was weaker and nonsignificant (OR
Several statistically significant associations were observed
between the respiratory conditions and occupational group-
ings (Table 4). A rtists, writers, decorators, and photographers
3.1) as well as the group of women in service occupa-
2.4) had a significantly increased risk of asthma.
8.7. Only 2.2% never worked;
There were nonsignificant elevated risks for asthma for the
following occupational groups: technologists and technicians
2.5, CI 0.79 to 9.1), food preparation (OR
to 17.6), precision production (OR
2.4, CI 0.5 to 11.5). The odds of chronic
bronchitis was significantly elevated (OR
of machine operators, assemblers, and inspectors. A sthma-
like symptoms were significantly more prevalent among nurses
and other nonphysician health care workers (
2.9), social workers (OR
2.4) than in the referent category. The data were reanalyzed
with “asthma” and “asthma-like” symptoms combined into a
single group. The results for nurses, social workers, and home-
makers continued to show statistically significant OR (2.3, 3.2,
and 2.6, respectively). The results for artists and photogra-
phers (1.6, 95% CI
0.7 to 3.3), food preparation workers
(1.7, 95% CI
0.6 to 5.1), and “other service occupations”
(1.4, 95% CI
0.8 to 2.6) showed OR 1.4 or greater, but none
was statistically significant.
The overall proportion of the female population previously
exposed to DGV FS was 21.2%. The proportion of exposed
subjects was highest in the following occupations: nurses,
92%; food services, 77%; precision production, 58%; other
services, 54%; machine operators, 50%; and technicians, 46%.
Exposure to DGV FS was associated with a significant in-
creased odds of asthma (OR
1.8), and with a marginally sig-
nificant increased odds of asthma-like symptoms (OR
CI 0.9 to 2.0) (Table 5). The odds of asthma due to occupation
increased with increasing duration of exposure both when
duration of exposure was treated as a categorical variable (Ta-
ble 5) and when it was considered as a continuous variable
(asthma: age-smoking-adjusted OR
3.5, CI 0.7
3.4, CI 0.7 to 17.1) and
5.2) in the group
2.9), and housewives (OR
1.02 to 1.56
RESPIRATORY FUNCTION IN WOMEN IN SPPARCS PROJECT BY RESPIRATORY HISTORY
No Conditions (
Adult Asthma (
* All lung function measures adjusted for age, height, and smoking.
Age–height–smoking-adjusted differences (95% CI) in means between subjects with the specific respiratory conditions and those without any respiratory conditions.
ADJUSTED ODDS RATIOS FOR THE ASSOCIATION BETWEEN SMOKING AND
SELF-REPORTED DOCTOR-DIAGNOSED RESPIRATORY CONDITIONS AND
SYMPTOMS AMONG OLDER WOMEN IN SONOMA, CA, 1994
Smoking Categories No ConditionsAdult Asthma
Never smoked445 2228 64
10 yr) 240
* Number in group, age-adjusted OR (95% CI) from multinomial logistic regression predicting respiratory conditions (no respiratory dis-
order as the reference group); four subjects had missing smoking data.
Forastiere, Balmes, Scarinci, et al.: Asthma and Occupation among Women
per 10 yr duration of exposure). A similar, but less strong
trend was observed for asthma-like symptoms (Table 5; OR ?
1.13, CI ? 0.96 to 1.3, per 10 yr duration of exposure). When
subjects were stratified by smoking history, an increased odds
of asthma with exposure to DGV FS was observed only in life-
long nonsmokers (OR 5.2) (Table 5).
Given the observed prevalence of ever-smoking in this
population (51.1%) and the observed overall odds for asthma
(OR ? 2.3) and asthma-like symptoms (OR ? 2.1) in subjects
who ever smoked cigarettes, the estimated PA R for smoking
were 40.5% and 35.0%, respectively (Table 6). PA R due to
occupational exposure to dusts, gas, vapors, fumes, or sensitiz-
ers were 15.1% and 7.5% for asthma and asthma-like symp-
toms, respectively. The estimates were slightly higher (20.0%
and 10.2%, respectively) when all the occupational groups that
were associated with respiratory conditions (Table 4: nurses, so-
cial workers, artists, technicians, food and other services occu-
pations, precision production and machine operators) were
merged to form an a posteriori “high-risk” group (reference
group ? all other occupations). The risk of asthma and asthma-
like symptoms was increased among the few subjects (4.0%)
who were still working and whose current occupation was
classified as “high-risk” (asthma: OR ? 2.7, CI ? 0.98 to 7.6;
OR ? 1.6, CI ? 0.7 to 3.6 for asthma-like symptoms), but the
estimates of the attributable risk (6.3% and 2.4%, respectively)
had wide confidence intervals.
No previous study has tried to quantify the burden of occupa-
tional factors on the distribution of respiratory conditions among
elderly women. Because asthma and chronic respiratory
symptoms are relatively frequent in older age and are an im-
portant cause of disability and health care costs, we consid-
ered it of interest to evaluate the contribution of occupational
factors for these conditions. Permanent impairment and dis-
ability have been described among patients with occupational
asthma, due to a persistence of the airways inflammatory pro-
cess even in absence of continued exposure (1).
This study shows that employment in a number of occupa-
tions is associated with an increased odds of self-reported,
doctor-diagnosed asthma and self-reported asthma symptoms
among older women. Moreover, employment in occupations
with a high probability of exposures to dusts, gas, vapors,
fumes, or sensitizers was a significant contributor to the bur-
den of asthma PA R ? 15 to 20%).
The increased risk of asthma in the category of artists, writ-
ers, decorators, and photographers is interesting, since few re-
ports are available on this group with a high potential for ex-
posure to several chemicals that may cause asthma. A rtists
and decorators may be exposed to low-molecular-weight agents,
including diisocyanates, anhydrides, dyes, resins, glues, and
metals. Occupational asthma has been described among pho-
tographers exposed to ethylenediamine (22) and to sodium
Women in “other service occupations” in this study were at
an increased risk of asthma. Most of the subjects in this group
were caretakers or cleaners, occupations in which the use of de-
tergents and solvents that have been associated with asthma is
common (1). Cleaners also were found to be at high risk of
asthma in a recent population study in Spain (8). Homemakers
may share the same type of exposure to detergents and solvents;
ASSOCIATION BETWEEN THE LONGEST OCCUPATION (SELECTED OCCUPATIONS) AND RESPIRATORY
DISORDERS AND SYMPTOMS IN OLDER WOMEN, SONOMA, CA, 1994
Occupation (1990 Census Code)No ConditionsAdult Asthma
Managers, professionals, and administrative occupations
Nurses and therapists (95–106)
391 2639 74
1.0 (reference) 1.0 (reference)
Teachers and librarians (113–165) 101
Social workers (166–177)1027
2.1 (0.4–11.0) 4.3‡ (1.6–12.1)
Artists, writers, decorators, photographers (183–199) 2825
0.8 (0.2–3.5) 1.0 (0.4–2.7)
Technologists and technicians (203–235)1823
0.9 (0.2–4.6)0.8 (0.2–3.0)
Sales occupations (243–285) 728 13
1.2 (0.5–2.6)1.0 (0.5–2.0)
Food preparation (433–444)1203
NC 1.1 (0.3–4.4)
Other service occupations (403–407, 445–469) 4959
0.9 (0.3–2.5)1.0 (0.5–2.2)
Farming, forestry, fishing (473–499) 3878
1.9 (0.8–4.8) 1.1 (0.5–2.4)
Precision production (628–699)1023
1.8 (0.4–9.0) 1.6 (0.4–6.3)
Machine operators, assemblers, and inspectors (703–799) 1351
5.2 (1.6–16.9)0.6 (0.1–4.5)
Homemakers not working outside of home 2018
0.3 (0.0–2.6)2.4 (1.0–6.1)
* Number, age–smoking-adjusted odds ratios (95% CI) from multinomial logistic regression with no respiratory conditions as the reference group and “managers, professionals,
and administrative occupations” as reference. NC ? odds ratio not calculated due to small numbers; 13 subjects were excluded since they were in occupations with four or fewer
† p ? 0.05.
‡ p ? 0.01.
AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINEVOL 1571998
and, therefore, it is not surprising that they have been found to
be at increased risk for both asthma and respiratory symptoms
in this study and in the study reported from Spain (8).
We found a significantly increased risk of asthma-like
symptoms among nurses and other nonphysician health work-
ers, approximately 80% of whom were nurses, with the others
falling into the categories of pharmacists, occupational, physi-
cal and speech therapists, and dietitians. These results are sim-
ilar to other reports that have documented occupational asthma
among nurses (17) and respiratory therapists (7). Workers in
these occupations may be exposed to several biologic agents
and to chemicals, (e.g., formaldehyde and glutaraldehyde). A l-
lergy caused by exposure to powdered latex gloves (24, 25)
also may contribute to the observed increased odds of symp-
toms. A lthough the results for nurses and other health work-
ers are easily interpretable and have a potentially large impact
for primary prevention, we have no good explanation for the
excess of asthma-like symptoms among social workers.
The other occupations, for which we observed nonsignifi-
cant but highly suggestive associations with asthma (techni-
cians, food workers, and farmers) have been associated with
asthma in other studies (8, 11). Other investigations have indi-
cated a strikingly elevated risk of asthma among farmers. In a
study among males and females in New Zealand, an odds ratio
ASSOCIATION BETWEEN OCCUPATIONAL EXPOSURE TO DUSTS, GAS, VAPORS, FUMES, OR
SENSITIZERS AND RESPIRATORY DISORDERS AMONG WOMEN IN SONOMA, CA, 1994
Occupational ExposureNo Conditions Adult Asthma
Unexposed 64944 74128
Duration of exposure, yr
Unexposed649 4474 128
1.0 (reference)1.0 (reference)
Unexposed371 11 2251
1.0 (reference) 1.0 (reference)
Unexposed278 33 5277
* Number, age–smoking-adjusted odds ratio (95% CI) from multinomial logistic regression predicting respiratory conditions (no respira-
tory conditions as the reference group). Occupational exposure to dusts, gas, vapors, fumes, or sensitizers based on a blind review of the
† p ? 0.05.
‡ p ? 0.01.
SMOKING AND OCCUPATION-RELATED PAR FOR ASTHMA AND ASTHMA-LIKE
SYMPTOMS AMONG WOMEN AGE ? 55 yr IN SONOMA, CA, 1994
Adult AsthmaAsthma-like Symptoms
Ever smoking 51.12.3 40.5%
Employment in “high-risk” occupations‡
Current employment in “high-risk” occupations‡
* Adjusted OR (95% CI) from multinomial logistic regression predicting respiratory conditions (no respiratory conditions as the reference
† Occupational exposure to gas, fumes, dust, and sensitizers based on a review of the occupational history.
‡ Occupational groups associated with an increased risk of asthma in the analysis presented in Table 4 (nurses, social workers, artists,
technicians, food and other services occupations, precision production and machine operators). All other occupations as reference.
Forastiere, Balmes, Scarinci, et al.: Asthma and Occupation among Women
of 4.3 was observed for the association between farming and
asthma (11). Our results for farmers, although suggestive of an
increased risk, are less striking than those from New Zealand.
Dairy farming and grape growing constitute the principal agri-
culture of the study community and may represent a different
set of exposures than those observed in the New Zealand
study. Moreover, women may have less intense exposures
than men who live and work in agricultural settings.
The significant association that we observed between expo-
sure to gas, fumes, dust, vapors, and sensitizers and asthma
parallels findings on asthma or wheeze in other population
studies that include both men and women (9, 10, 26). In our
study, subjects with the longest duration of exposure to these
agents had the highest risk. X u and Christini (10) found an as-
sociation between asthma and cumulative exposure but not
with duration of exposure. Flodin and colleagues found a sig-
nificant relation with self-reported probability of exposure
(26). In contrast to most published studies that have used self-
reports of exposure to DGV FS (10, 12, 27), we assigned expo-
sure to these agents after a blinded review (with regard to
health status) of the individual occupational history, as has
been done previously (28, 29) in two studies of asthma. A l-
though not widely used in respiratory epidemiology, this ap-
proach has been applied extensively in epidemiologic studies
of occupational cancer (30). V alidity studies tend to suggest
that self-report of exposure is probably an inadequate tool for
the collection of information on occupational exposure in
community studies, and that a detailed job description together
with expert assessment would be preferred (31).
Recently, investigators have speculated that occupational
asthma is more common in women than had been previously
believed (8). Several European studies have identified high
risks for respiratory symptoms among women exposed in a va-
riety of occupational settings (17, 27, 32). A higher PA R was
identified in females in comparison to males in a recent popu-
lation study in Spain (8). V iegi and coworkers speculated that
adult women are more susceptible than men to chemical sub-
stances that can irritate airway receptors (27). Our PA R esti-
mate for asthma (15 to 20%) and asthma-like symptoms (7.5
to 10%) may appear surprisingly high for a population of
women who live in a nonindustrialized area. While the use of
an a posteriori classification may have led to a somewhat in-
creased estimate, nonetheless, the estimates from this study
are consistent with previous work in the U.S. Based on data
from the 1978 Survey of Disability and Work, Blanc estimated
that 15% of asthma among adults could be related to occupa-
tional exposures (6). Similar estimates have been provided in
a study from Michigan (10 to 18%) (33) and in another study
from the San Francisco Bay A rea (6 to 14%) (29).
We found that cigarette smoking clearly is associated with
asthma, chronic bronchitis, and asthma-like symptoms. Cur-
rent smokers, however, were at increased risk of chronic bron-
chitis and wheeze but not of asthma. A recent report from the
Nurses’ Health Study in the U.S. (11) has shown an increased
risk among former smokers but not among current smokers.
Sex differences in the role of smoking in the occurrence of
asthma and chronic wheeze has been controversial because of
problems of diagnostic bias. In our data, females were more
likely to report a doctor’s diagnosis of asthma or chronic bron-
chitis than males; and males tended to have more asthma-like
symptoms without a specific doctor’s diagnosis. Unfortu-
nately, we have no data that would permit us to determine
whether a physician’s knowledge of a woman’s occupation in-
fluenced the diagnosis of asthma, chronic bronchitis, or em-
Our study did not have the power to study properly how
smoking and occupational exposure may interact in relation to
the occurrence of asthma and chronic asthma-like symptoms.
However, we found that the increased odds of asthma due to
occupational exposure were mainly present among nonsmok-
ers. A t least two studies (12, 27) have addressed the issue of
the combined effect of smoking and occupational exposure on
chronic respiratory symptoms. In data from the Six Cities
Study, Korn and associates (12) found an independent effect
of current occupation and smoking on symptom prevalence.
On the other hand, V iegi and coworkers (27) reported that the
effect of occupational exposure on several respiratory catego-
ries (including wheeze and asthma) was higher among non-
smokers than among smokers.
There is no universally accepted definition of asthma for
use in epidemiologic studies. However, in the absence of a
measure of bronchial reactivity to supplement a report of
wheezing (34), a self-report of a doctor’s diagnosis of asthma
is used most frequently to classify subjects as asthmatic. We
followed this convention. Obviously, we cannot be certain that
some subjects in the group with “asthma-like” symptoms, in
fact, have asthma. We believe that our choice is supported by
the pulmonary function data that are presented in Table 2,
which show that, for all measures, subjects with a doctor’s di-
agnosis of asthma have substantially lower levels than those with
asthma-like symptoms. These findings are consistent with other
epidemiologic studies (34). Because “asthma” and “asthma-
like symptoms” do not necessarily measure exactly the same
pathophysiologic entities, we separated them in our classifica-
tion. We adopted a “mutually exclusive” classification because
we wanted to isolate asthma, at least as diagnosed by physi-
cians and reported by subjects, from “chronic bronchitis?em-
physema,” which is more likely to be related to smoking. The
data in Table 3 indicate that those with “asthma” and “asthma-
like symptoms” were significantly less likely either to be cur-
rent smokers or to have quit smoking in the past 10 yr than
subjects who were labeled as having chronic obstructive pul-
monary disease, which would help to justify our a priori deci-
sion about the classification.
A limitation of this cross-sectional study is that the expo-
sure and the outcome depended on answers to questionnaires.
In addition, we did not have information on all the of the jobs
that might have been held by the subjects, nor did we have in-
formation that would have permitted us to determine the rela-
tionship between the onset of adult asthma and the duration
of employment in a particular occupation at the time of onset.
Only the last job and the longest occupation in which the sub-
ject was employed were ascertained. These limitations were
imposed by the length of the questionnaire as it related to the
main focus of the study. Therefore, misclassification of expo-
sure could be an issue, since we cannot rule out the possibility
that diseased subjects may have recalled their occupation bet-
ter than healthy individuals. However, the study was focused
on physical function and performance rather than on occupa-
tion, making it unlikely that recall bias occurred with respect
to the relationship between occupation and chronic respira-
tory diagnoses and?or symptoms. Finally, the lack of data on
time of onset in relationship to employment leaves open the
possibility that the magnitude of the reported association could
be biased upward. However, the consistency of our findings
with others suggests that any such bias is likely to be small.
In conclusion, these data indicate that occupational expo-
sures may be an important contributor to the occurrence and?
or persistence of asthma in older women. Prospective popula-
tion-based studies of younger adults should include detailed
occupational histories to clarify the validity and strength of
the relationships reported herein.
AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE VOL 1571998
Acknowledgments: The study was performed while Francesco Forastiere
was visiting the School of Public Health, Division of Public Health Biology
and Epidemiology, University of California at Berkeley, Berkeley, CA, whose
hospitality is gratefully acknowledged. The authors thank Jackie Smith; Patti
LeBlanc; Jan Hansen; Janet Theissen; Cynthia Fleischer; Virginia Weisel; Joan
Steir and Jane Josselyn, who interviewed the subjects; Donna Turner, who
performed the pulmonary function testing; and Ann Swanson who pro-
vided programming assistance.
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