Table
16. Epidemiologic studies of bronchitis in workers exposed to silica
dust
|
Reference
and country
|
Study
design, cohort, and followup
|
Subgroup
|
Bronchitis
cases in subgroup*
|
Risk
measure
(OR)
|
95%
CI
|
Adjusted
for smoking
|
Comments
|
Clark
et al. [1980], United States |
Cross-sectional
study of bronchitic symptoms in 249 white male taconite miners; mean
age was 49 with >20 yr of exposure to taconite dust. Control
group of 86 men with no history of exposure to taconite mine dust. |
80
dust-exposed smokers with cough all day |
24%
|
|
|
Yes
|
Note
that subgroups represent bronchitic symptomsnot cases.
33 controls were employees of a school; however, occupations of the
other controls were not reported. Occupational dust exposures to the
control group may have contributed to the similar or higher prevalences
of bronchitic symptoms in that group. |
52
dust-exposed nonsmokers with cough all day |
1%
|
|
|
24
nondust-exposed nonsmokers with cough all day |
1%
|
|
|
32
nondust-exposed smokers with cough all day |
16%
|
|
|
80
dust-exposed smokers with phlegm all day |
18%
|
|
|
24
nondust-exposed nonsmokers with phlegm all day
|
1%
|
|
|
32
nondust-exposed smokers with phlegm all day |
37%
|
|
|
Cowie
and Mabena [1991], South Africa |
Cross-sectional
study of 1,197 black, male underground gold miners aged 2876
with 25.1 yr since first exposure (mean). 857 miners had chronic silicosis. |
Miners
with chronic sputum production and "high" dust exposure |
|
1.8§
|
1.192.69
|
Yes
|
62%
of miners who smoked and 45% of miners who never smoked had "chronic
bronchitic symptom complex."
"High"
and "low" dust exposure categories were based on qualitative
assessments of underground mine dust exposure and occupation.
Authors
stated that bronchitic symptoms may also have been related to underground
mining exposures other than respirable quartz dust.
|
Miners
with 24 pack-yr of smoking exposure and chronic sputum production |
|
3.7
|
2.625.23**
|
Holman
et al. [1987], Australia |
Cross-sectional
study of 1,363 male, current gold miners (51% were underground miners)
aged 20 to >60. 53% of the cohort worked underground 119
yr. |
Total
cohort |
14%
|
|
|
Yes
|
ORs
were based on comparison with nonminers and were adjusted for effects
of smoking and age. |
Miners
with chronic bronchitis:
|
19
yr of underground gold mining |
|
1.8
|
1.03.3
|
1019
yr of underground gold mining |
|
2.5
|
1.25.2
|
>20
yr of underground gold mining |
|
5.1
|
2.410.9
|
Kreiss
et al. [1989b], United States |
Community-based
cross-sectional study of 389 male residents of Leadville, CO. 281
(72.2%) of the sample had worked at the local molybdenum mine. Mean
yr of exposure: 9.3. Mean age of cohort: 44. |
Underground
miners with >10 yr of employment: |
Yes
|
ORs
were based on comparison with residents having no history of occupational
dust exposure.
Nearly
half (49%) of personal samples for quartz exposures among the miners
exceeded the NIOSH REL of
0.05 mg/m3 (total number of samples was not reported).
|
With
chronic
cough |
|
0.84
|
0.371.90
|
With
chronic
phlegm |
|
0.93
|
0.422.06
|
Ng
et al. [1992b], Singapore |
Cross-sectional
study of 85 granite quarry workers with "high" dust exposure
and 154 quarry workers with "low" dust exposure (see comments);
mean age was 42. Mean duration of employment was 13.7 yr. Comparison
group of
148 male postal workers with no exposure to granite dust; mean age
was 40. |
Quarry
workers with "high" dust exposure: |
Yes
|
No
quantitative exposure concentrations for dust or silica were reported:
granite quarry rock drillers and rock crushers were assumed to have
"high" silica exposure; and administrative workers, truck
drivers, vehicle maintenance workers, and loader operators were assumed
to have "low" silica exposure.
Results
were adjusted for effects of age.
|
All
(85) |
9
|
|
|
Nonsmokers
(34) |
2
|
§§
|
|
Ex-smokers
(5) |
|
|
|
Current
smokers
(46) |
7
|
§§
|
|
Rastogi
et al. [1991], India |
Cross-sectional
study of
240 male and
102 female agate grinders and chippers, and 116 male and 33 female
controls with nondusty occupations. The mean duration of exposure
was 10 yr for males and 8.9 yr for females. |
Chronic
bronchitis: |
Yes
|
Association
between dust exposure and chronic bronchitis may not have been detected
because the control group included workers who may have occupational
exposure to respirable silica dust (e.g., rickshaw-pullers and sweepers).
High prevalence of tuberculosis in agate workers and controls may
have masked an association for bronchitis. |
Male:
|
Agate
workers
|
3.75/100
|
|
|
Controls
|
4.58/100
|
|
|
Female:
|
Agate
workers
|
0
|
|
|
Controls
|
9.1/100
|
|
|
Acute
bronchitis: |
Male:
|
Agate
workers
|
9.1/100
|
|
|
Controls
|
5.17/100
|
|
|
Female:
|
Agate
workers
|
9.8/100
|
P<0.05
|
|
Controls
|
0
|
|
|
Samet
et al. [1984], United States |
Cross-sectional
study of 192 male, current underground uranium miners aged <40,
4059, and >60. 145 miners (76%) mined >10
yr underground. |
Miners
with chronic cough: |
Yes
|
Chronic
cough and chronic phlegm were not associated with duration of silica
exposure in multiple logistic regression analysis (results were not
reported). |
1019
yr of
mining |
14.1/100***
|
|
|
>20
yr of mining |
22.7/100***
|
|
|
Miners
with chronic phlegm: |
1019
yr of
mining |
31.9/100***
|
|
|
>20
yr of mining |
36.6/100***
|
|
|
Sluis-Cremer
et al. [1967],
South Africa |
Community-based,
cross-sectional study of chronic bronchitis in 827 male residents
who were aged >35 and who lived in Carletonville, a South African
town with four gold mines. |
Residents
with chronic bronchitis:
|
Yes
|
"Dust-exposed"
was defined as self-reported occupational exposure in a "scheduled
dusty area" of a mine.
A
significant difference existed between the prevalence of chronic
bronchitis in dust-exposed smokers and nondust-exposed smokers (P<0.01).
No
significant difference existed between dust-exposed and nondust-exposed
nonsmokers or ex-smokers.
|
Dust-exposed: |
Smokers |
199/394
(51%)
|
|
|
Nonsmokers |
22/168
(13%)
|
|
|
Nondust-exposed: |
Smokers |
45/161
(28%)
|
|
|
Nonsmokers
and ex-
smokers |
7/104
(7%)
|
|
|
Wiles
and Faure [1977],
South Africa |
Cross-sectional
study of chronic bronchitis in 2,209 underground gold miners (race
not reported) aged 4554 with >10 yr of employment.
653 were ex-miners for >1 yr. |
138
miners in highest cumulative dust exposure group: |
Yes
|
Prevalence
of chronic bronchitis increased with increasing mean dust concentration
(P<0.001) and with cumulative dust exposure in nonsmokers
(P<0.05), ex-smokers (P<0.05), and smokers (P<0.001). |
Nonsmokers
|
2/14 (14%)
|
|
|
Ex-smokers
|
4/31
(13%)
|
|
|
Smokers
|
47/93
(51%)
|
|
|
*Number
of cases unless otherwise indicated.
Abbreviations: CI=confidence interval; NIOSH=National
Institute for Occupational Safety and Health; OR=odds ratio; REL=recommended
exposure limit.
Dash indicates not reported.
§Compared with miners having "low" dust
exposure.
**Compared with miners having 0 pack-yr.
Estimated prevalence.
Risk measure was not reported, but P<0.01
compared with controls.
§§Risk measure was not reported, but P>0.05
compared with controls.
***Standardized to the overall distribution of cigarette
smoking. |