Occupational exposure to crystalline silica and risk of systemic lupus erythematosus: a population-based, case-control study in the southeastern United States.
OBJECTIVE
Crystalline silica may act as an immune adjuvant to increase inflammation and antibody production, and findings of occupational cohort studies suggest that silica exposure may be a risk factor for systemic lupus erythematosus (SLE). We undertook this population-based study to examine the association between occupational silica exposure and SLE in the southeastern US.


METHODS
SLE patients (n = 265; diagnosed between January 1, 1995 and July 31, 1999) were recruited from 4 university rheumatology practices and 30 community-based rheumatologists in 60 contiguous counties. Controls (n = 355), frequency-matched to patients by age, sex, and state of residence, were randomly selected from driver's license registries. The mean age of the patients at diagnosis was 39 years; 91% were women and 60% were African American. Detailed occupational and farming histories were collected by in-person interviews. Silica exposure was determined through blinded assessment of job histories by 3 industrial hygienists, and potential medium- or high-level exposures were confirmed through followup telephone interviews. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were estimated by logistic regression.


RESULTS
More patients (19%) than controls (8%) had a history of medium- or high-level silica exposure from farming or trades. We observed an association between silica and SLE (medium exposure OR 2.1 [95% CI 1.1-4.0], high exposure OR 4.6 [95% CI 1.4-15.4]) that was seen in separate analyses by sex, race, and at different levels of education.


CONCLUSIONS
These results suggest that crystalline silica exposure may promote the development of SLE in some individuals. Additional research is recommended in other populations, using study designs that minimize potential selection bias and maximize the quality of exposure assessment.
Epidemiology Branch, National Institute of Environmental Health Sciences, National Institutes of Health, Durham, North Carolina 27709, USA. parks@niehs.nih.gov
Christine G
CG
Parks
Glinda S
GS
Cooper
Leena A
LA
Nylander-French
Wayne T
WT
Sanderson
John M
JM
Dement
Philip L
PL
Cohen
Mary Anne
MA
Dooley
Edward L
EL
Treadwell
E William
EW
St Clair
Gary S
GS
Gilkeson
Jane A
JA
Hoppin
David A
DA
Savitz
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D004522:Educational Status; D005260:Female; D006801:Humans; D016015:Logistic Models; D008180:Lupus Erythematosus, Systemic / Q000139:chemically induced* / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D016273:Occupational Exposure; D015995:Prevalence; D044469:Racial Groups; D012822:Silicon Dioxide / Q000009:adverse effects*; D015144:Southeastern United States / Q000453:epidemiology
D012822:Silicon Dioxide