NIOSH
HAZARD REVIEW
Health
Effects of Occupational Exposure
to
Respirable Crystalline Silica
|
Table
16. Epidemiologic studies of bronchitis in workers exposed to silica
dust
|
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|
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 symptoms—not 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 28–76 with 25.1 yr since first exposure (mean). 857 miners had chronic silicosis. | Miners with chronic sputum production and "high" dust exposure |
—
|
1.8§
|
1.19–2.69
|
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 |
2.62–5.23** |
||||
| 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 1–19 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:
|
|||||||
| 1–9 yr of underground gold mining |
—
|
1.8
|
1.0–3.3
|
||||
| 10–19 yr of underground gold mining |
—
|
2.5
|
1.2–5.2
|
||||
| >20 yr of underground gold mining |
—
|
5.1
|
2.4–10.9
|
||||
| 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 |
|||
| With
chronic cough |
—
|
0.84
|
0.37–1.90
|
||||
| With
chronic phlegm |
—
|
0.93
|
0.42–2.06
|
||||
| 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. |
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| 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, 40–59, 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). | |||
| 10–19
yr of mining |
14.1/100***
|
—
|
—
|
||||
| >20 yr of mining |
22.7/100***
|
—
|
—
|
||||
| Miners with chronic phlegm: | |||||||
| 10–19
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. |
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| 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 45–54 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. |
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