Maternal occupational exposure to selected organic and chlorinated solvents and delivery of small-for-gestational age or preterm infants.

BACKGROUND: Potential reproductive effects of organic solvent exposure during pregnancy remain unclear. We investigated the association between maternal occupational exposure during pregnancy to six chlorinated solvents, three aromatic solvents, and Stoddard solvent, and delivery of preterm infants or those born small-for-gestational age (SGA). METHODS: In this case-control study of SGA and preterm birth (PTB) nested within the National Birth Defects Prevention Study (NBDPS) from 1997 to 2011, we analyzed data from 7504 singleton live births without major birth defects and their mothers. Self-reported information on jobs held in the periconceptional period was assessed for solvent exposure. Unconditional logistic regression was used to estimate the association between maternal occupational exposure (any, none) during early pregnancy to organic solvents and PTB and SGA. Linear regression was used to examine changes in mean birthweight potentially associated with maternal occupational solvent exposure. RESULTS: Maternal occupational exposure to any organic solvents overall was not associated with an increased odds of PTB (adjusted odds ratio [aOR] = 0.94; 95% confidence interval [CI] 0.67-1.33) or SGA (aOR = 0.93; 95% CI 0.65-1.34). Point estimates increased modestly for higher estimated exposure versus lower, but confidence intervals were wide and not statistically significant. Maternal exposure to solvents was not associated with a statistically significant change in term birthweight among infants. CONCLUSIONS: Occupational exposure to organic solvents at the frequency and intensity levels found in a population-based sample of pregnant workers was not associated with PTB or SGA; however, we cannot rule out any effects among pregnant workers with uncommonly high exposure to organic solvents.

Evidence of nickel and other trace elements and their relationship to clinical findings in acute Mesoamerican Nephropathy: A case-control analysis.

BACKGROUND: Although there are several hypothesized etiologies of Mesoamerican Nephropathy (MeN), evidence has not yet pointed to the underlying cause. Exposure to various trace elements can cause the clinical features observed in MeN. METHODS AND FINDINGS: We measured 15 trace elements, including heavy metals, in renal case-patients (n = 18) and healthy controls (n = 36) in a MeN high-risk region of Nicaragua. Toenails clippings from study participants were analyzed using inductively coupled plasma mass spectrometry. A case-control analysis was performed, and concentrations were also analyzed over participant characteristics and clinical parameters. Nickel (Ni) concentrations were significantly higher in toenails from cases (1.554 mg/kg [0.176-42.647]) than controls (0.208 mg/kg [0.055-51.235]; p<0.001). Ni concentrations correlated positively with serum creatinine levels (p = 0.001) and negatively with eGFR (p = 0.001). Greater Ni exposure was also associated with higher leukocyte (p = 0.001) and neutrophil (p = 0.003) counts, fewer lymphocytes (p = 0.003), and lower hemoglobin (p = 0.004) and hematocrit (p = 0.011). CONCLUSIONS: Low-dose, chronic environmental exposure to Ni is a possible health risk in this setting. Ni intoxication and resulting systemic and renal effects could explain the clinical signs observed during early MeN. This study provides compelling evidence for a role of Ni in the acute renal impairment observed in this MeN high-risk population. Additional work to assess exposure levels in a larger and heterogeneous population, identify environmental sources of Ni and exposure pathways, and evaluate the link between Ni and MeN pathogenesis are urgently needed.

Development of Job Exposure Matrices to Estimate Occupational Exposure to Solar and Artificial Ultraviolet Radiation.

OBJECTIVES: Job exposure matrices (JEMs) are important tools for estimating occupational exposures in study populations where only information on industry and occupation (I&O) are available. JEMs The objective of this work was to create JEMs for solar and artificial ultraviolet radiation (UVR) using a US standardized coding scheme. METHODS: Using U.S. Census Bureau industry and occupation codes, separate lists of I&O pairs were developed for solar and artificial UVR by a panel of Certified Industrial Hygienists who assigned exposure ratings to I&O pairs with potential exposure. Parameters for exposure included prevalence (P) and frequency (F) for solar UVR and P, F, and intensity (I) for artificial UVR. Prevalence, or percent of all workers employed in an I&O pair who were exposed, was categorically rated: 0 to <1, 1 to <20; 20 to <80, and ≥80. Frequency of exposure, defined by the number of hours per week workers were exposed, was categorically rated: 0 to <5, 5 to <20, 20 to <35, and ≥35 h per week. For artificial UVR only, intensity of exposure was assigned three ratings: low, low with rare excursions, and >low under normal conditions. Discrepant ratings were resolved via consensus. RESULTS: After excluding I&O pairs assigned P and F ratings of 0 (solar UVR) and P, F, and I ratings of 0 (artificial UVR) from the JEM, 9206 I&O pairs were rated for solar UVR and 2010 I&O pairs for artificial UVR. For solar UVR, 723 (7.9% of all rated pairs) had ratings in the highest category for P and F; this group included 45 occupations in varied industries. Construction and extraction occupations represented most of the occupations (n = 20; 44%), followed by farming, fishing, and forestry occupations (n = 6; 13%). For artificial UVR, 87 I&O pairs (4.3% of all rated pairs) had maximum ratings for P, F, and I; these comprised a single occupation (welding, soldering, and brazing workers) in diverse industries. CONCLUSIONS: JEMs for solar and artificial UVR were developed for a broad range of I&O pairs in the US population and are available for use by researchers conducting occupational epidemiological studies.

Maternal occupational pesticide exposure and risk of congenital heart defects in the National Birth Defects Prevention Study.

BACKGROUND: Congenital heart defects (CHDs) are common birth defects, affecting approximately 1% of live births. Pesticide exposure has been suggested as an etiologic factor for CHDs, but previous results were inconsistent. METHODS: We examined maternal occupational exposure to fungicides, insecticides, and herbicides for 3328 infants with CHDs and 2988 unaffected control infants of employed mothers using data for 1997 through 2002 births from the National Birth Defects Prevention Study, a population-based multisite case-control study. Potential pesticide exposure from 1 month before conception through the first trimester of pregnancy was assigned by an expert-guided task-exposure matrix and job history details self-reported by mothers. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using multivariable logistic regression. RESULTS: Maternal occupational exposure to pesticides was not associated with CHDs overall. In examining specific CHD subtypes compared with controls, some novel associations were observed with higher estimated pesticide exposure: insecticides only and secundum atrial septal defect (OR = 1.8; 95% CI, 1.3-2.7, 40 exposed cases); both insecticides and herbicides and hypoplastic left heart syndrome (OR = 5.1; 95% CI, 1.7-15.3, 4 exposed cases), as well as pulmonary valve stenosis (OR = 3.6; 95% CI, 1.3-10.1, 5 exposed cases); and insecticides, herbicides, and fungicides and tetralogy of Fallot (TOF) (OR = 2.2; 95% CI, 1.2-4.0, 13 exposed cases). CONCLUSION: Broad pesticide exposure categories were not associated with CHDs overall, but examining specific CHD subtypes revealed some increased odds ratios. These results highlight the importance of examining specific CHDs separately. Because of multiple comparisons, additional work is needed to verify these associations.

Body mass index, asthma and exhaled nitric oxide in U.S. adults, 2007-2010.

OBJECTIVE: Increases in asthma and obesity over the past three decades have led to speculation about a causal link between the two diseases. However, investigations of the relationship between body mass index (BMI) and fractional exhaled nitric oxide (FeNO) - a marker of eosinophilic airway inflammation - have produced mixed results. The purpose of this study was to evaluate the relationship between body mass index (BMI), asthma and FeNO in a sample of U.S. adults using data from the National Health and Nutrition Examination Surveys (NHANES) for 2007-2010. METHODS: We assessed the relationship between FeNO and BMI in subjects with and without asthma using categorical and continuous models for BMI. All models controlled for age, gender, ethnicity, household income-to-poverty ratio, atopy and current smoking. RESULTS: Adjusted asthma prevalence was positively associated with BMI, and subjects with asthma had higher adjusted FeNO levels than subjects without asthma. However, no association between FeNO and BMI was observed in either those with (ß = 0.002, p = 0.74) or without (ß = 0.0014, p = 0.51) asthma after adjusting for covariates. CONCLUSIONS: Our results suggest that in the U.S. adult population, BMI is not associated with eosinophilic airway inflammation.

Maternal occupational pesticide exposure and risk of hypospadias in the National Birth Defects Prevention Study.

BACKGROUND: Hypospadias is a common congenital malformation among men in which the urethral opening is ventrally displaced. Pesticide exposure has been suggested as a possible etiologic factor, but previous epidemiologic studies have produced inconsistent results. METHODS: We used data from the National Birth Defects Prevention Study (NBDPS), a population-based case-control study, to examine maternal occupational exposure to fungicides, insecticides, and herbicides among 647 hypospadias case infants and 1496 unaffected male control infants with estimated delivery dates from October 1997 to December 2002. Periconceptional (1 month before conception through the first trimester of pregnancy) pesticide exposures were assigned by an expert rater, assisted by a job-exposure matrix (JEM), from a job history completed by mothers during a telephone interview. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated with multivariable logistic regression, and adjusted for relevant covariates. RESULTS: Maternal periconceptional occupational exposure to any pesticides (yes/no) was not associated with an increased risk of hypospadias (OR = 0.78; 95% CI = 0.61-1.01). Maternal occupational periconceptional pesticide exposure type (insecticides, fungicides, and herbicides) and estimated quantity also showed no significantly increased risk of hypospadias and no evidence of a dose-response relationship; however, the estimated pesticide exposure levels in this population were low. CONCLUSION: Using broad classes of insecticides, herbicides, and fungicides, we found no evidence that low intensity maternal periconceptional occupational pesticide exposure was a risk factor for hypospadias.

Prevalence of beryllium sensitization among Department of Defense conventional munitions workers at low risk for exposure.

OBJECTIVE: To estimate the prevalence of beryllium sensitization among former and current Department of Defense workers from a conventional munitions facility. METHODS: Participants were screened by using Beryllium Lymphocyte Proliferation Test. Those sensitized were offered clinical evaluation for chronic beryllium disease. RESULTS: Eight (1.5%) of 524 screened workers were found sensitized to beryllium. Although the confidence interval was wide, the results suggested a possibly higher risk of sensitization among workers exposed to beryllium by occasional resurfacing of copper-2% beryllium alloy tools compared with workers with the lowest potential exposure (odds ratio = 2.6; 95% confidence interval, 0.23-29.9). CONCLUSIONS: The findings from this study suggest that Department of Defense workers with low overall exposure to beryllium had a low prevalence of beryllium sensitization. Sensitization rates might be higher where higher beryllium exposures presumably occurred, although this study lacked sufficient power to confirm this.

Risk of beryllium sensitization in a low-exposed former nuclear weapons cohort from the Cold War era.

BACKGROUND: The nuclear weapons industry has long been known as a source of beryllium exposure. METHODS: A total of 1,004 former workers from a nuclear weapons assembly site in the Midwest were screened for sensitization to beryllium (BeS). The screenings were part of the Department of Energy (DOE) Former Worker Program established in 1996. RESULTS: Twenty-three (2.3%) workers were found sensitized to beryllium and this prevalence was comparable to other DOE sites. Occasional, direct exposure to beryllium through machining and grinding of copper-beryllium (Cu-Be) 2% alloy tools was found to increase the risk of sensitization compared to background exposure (OR = 3.83; 95% CI: 1.04-14.03) with a statistically significant trend (P = 0.03) revealing that particular jobs are associated with sensitization. Exposure potential in this study was estimated based on job titles and not personal exposure information. CONCLUSIONS: These results confirm the need to screen workers using beryllium alloy tools in other industries and for consideration of altering work practices.

Occupational exposure to pesticides, metals, and solvents: the impact on mortality rates in the Honolulu Heart Program.

OBJECTIVE: To investigate the impact of occupational exposure to pesticides, metals, and solvents on mortality. PARTICIPANTS: Middle-aged Japanese-American men (n = 7,540) who had participated in the Honolulu Heart Program during 1965-1968. METHODS: Industrial hygienists assessed participants' potential for exposure based on their primary job. Cumulative exposure scores were categorized as none, low, medium, and high. The underlying cause of death was ascertained by a physician panel. All associations were assessed using Cox proportional hazards models. RESULTS: A total of 4, 485 deaths occurred. Compared to no exposure, pesticide exposure was significantly associated with mortality from all causes, circulatory diseases, stroke, and all cancers. Results for all-cause mortality at the 0-yr lag after risk-factor adjustment were: Low, hazard ratio (HR) = 0.85, 95% confidence interval (CI)=0.68-1.08; medium, HR = 1.18, 95% CI = 1.01-1.37; and high, HR = 1.29, 95% CI = 1.06-1.57; trend, p=0.002. Exposure to metals and solvents was significantly associated with mortality from all causes, cancer, and respiratory disease, and exposure to solvents was additionally associated with mortality from circulatory disease. Associations were strongest at the 15-yr lag. CONCLUSIONS: Results show that occupational exposures to pesticides, metals, and solvents during mid-life are independently associated with increased mortality, and indicate potential importance of exposures that occurred approximately 15 years prior to death.

Beryllium surface levels in a military ammunition plant.

This study evaluated the presence of beryllium surface contamination in a U.S. conventional munitions plant as an indicator of possible past beryllium airborne and skin exposure and used these measurements to classify job categories by potential level of exposure. Surface samples were collected from production and nonproduction areas of the plant and at regional industrial reference sites with no known history of beryllium use. Surface samples of premoistened wiping material were analyzed for beryllium mass content using inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and results expressed as micrograms of beryllium per 100 square centimeters (micro g/100 cm(2)). Beryllium was detected in 87% of samples collected at the munitions plant and in 72% of the samples collected at regional reference sites. Two munitions plant samples from areas near sanders and grinders were above 3.0 micro g/100 cm(2) (U.S. Department of Energy surface contamination limit). The highest surface level found at the reference sites was 0.44 micro g/100 cm(2). Workers in areas where beryllium-containing alloy tools were sanded or ground, but not other work areas, may have been exposed to airborne beryllium concentrations above levels encountered in other industries where metal work is conducted. Surface sampling provided information useful for categorizing munitions plant jobs by level of past beryllium airborne and skin exposure and, subsequently, for identifying employees within exposure strata to be screened for beryllium sensitization.

Occupational exposures and movement abnormalities among Japanese-American men: the Honolulu-Asia Aging Study.

OBJECTIVE: The authors analyzed data on 1,049 men aged 71-93 years (excluding those with prevalent Parkinson's disease and stroke) from the Honolulu Heart Program (1965-1968) and the Honolulu-Asia Aging Study (1991-1999) to determine whether occupational exposures to pesticides, solvents, metals, manganese, and mercury during middle age were associated with 14 movement abnormalities 25 years later. METHODS: Analyses of variance and multivariate logistic regression were used to assess associations of interest. RESULTS: After adjustment for age, BMI, cognitive functioning, smoking, alcohol drinking, education, and physical activity, there was a positive association between abnormal 'facial expression' and the highest exposure to metals [odds ratio (OR) = 2.62; 95% confidence interval (CI) = 1.35-5.11; trend, p = 0.02], and the highest exposure to mercury (OR = 1.91; 95% CI = 1.04-3.49; trend, p = 0.03). Age was positively associated with all movement abnormalities, and cognitive function, body mass index and physical activity were inversely associated with most movement abnormalities. CONCLUSION: Higher exposure to any metal, and specifically mercury, was associated with abnormal facial expression.

Gliomas and farm pesticide exposure in women: the Upper Midwest Health Study.

An excess incidence of brain cancer in male farmers has been noted in several studies, but few studies have focused on women. The National Institute for Occupational Safety and Health Upper Midwest Health Study evaluated effects of rural exposures for 341 female glioma cases and 528 controls, all adult (18-80 years of age) nonmetropolitan residents of Iowa, Michigan, Minnesota, and Wisconsin. On average, controls lived longer on farms than did cases. After adjusting for age, age group, education, and farm residence, no association with glioma was observed for exposure to arsenicals, benzoic acids, carbamates, chloroacetanilides, dinitroanilines, inorganics, organochlorines, organophosphates, phenoxys, triazines, or urea-based or estrogenic pesticides. An increased risk of glioma was observed for carbamate herbicides but was not statistically significant (odds ratio = 3.0; 95% confidence interval, 0.9-9.5). No association was observed between glioma and exposure to 12 widely used specific pesticides, after adjustment for age, age group, education, and any other pesticide exposure. These results were not affected after exclusion of proxy respondents (43% of cases, 2% of controls). Women were less likely than men to have applied pesticides, but more likely to have laundered pesticide-contaminated clothes. Storing pesticides in the house was associated with a statistically non-significant increased risk. Results show that exposure to pesticides was not associated with an increased risk of intracranial gliomas in women. Other farm-related factors could be etiologic factors and will be discussed in future reports.

Nicotine exposure and decontamination on tobacco harvesters' hands.

Green tobacco sickness is an illness associated with nicotine exposures among tobacco harvesters. Agricultural workers manually harvest tobacco and thus have the potential for skin exposure to nicotine, particularly on the hands. Often gloves are not worn as it hinders the harvesters' ability to harvest the tobacco leaves. The purposes of this study were to measure the concentration of nicotine residue on the hands of tobacco harvesters and the effectiveness of hand washing at removing the residue. Wipe samples from the hands of 12 tobacco harvesters were collected at the end of morning and afternoon work periods over two consecutive days. Each harvester had one hand wiped before washing his hands, and the other hand wiped after washing his hands with soap and water. Eight samples per worker were collected over the two days for a total of 96 samples collected. In addition to the hand-wipe samples, leaf-wipe samples were collected from 15 tobacco plants to estimate the amount of nicotine residue on the plants. The average nicotine level in leaf-wipe samples was 1.0 microg cm(-2). The geometric mean pre-wash and post-wash nicotine levels on the hands were 10 and 0.38 microg cm(-2), respectively. Nicotine leaf-wipe level, right or left hand and time of sampling did not significantly influence exposure. Job position-working on the bottom versus the top of the tobacco harvesting machine-was associated with nicotine levels. Pre-wash nicotine levels were higher for workers on the bottom of the harvester but not significantly higher (P = 0.17). Post-wash nicotine levels were significantly higher for workers on the bottom of the harvester (P = 0.012). A substantial amount of nicotine was transferred to the hands, but washing with soap and water in the field significantly reduced nicotine levels by an average of 96% (P < 0.0001).

Comparing questionnaire-based methods to assess occupational silica exposure.

BACKGROUND: Epidemiologic assessment of occupational exposure to silica is typically limited to long-term work in the dusty trades, primarily in jobs held by men. We compared alternative questionnaire-based methods to assess silica exposure in a recent case-control study of 265 patients with systemic lupus erythematosus (mostly women) and 355 controls randomly selected from state driver's license registries and frequency-matched by age and sex. METHODS: In-person interviews included a job history (all jobs held at least 12 months) and checklist of silica-related jobs and tasks (work of at least 2 weeks). Three industrial hygienists reviewed job descriptions without knowing case-control status. Potential high- or moderate-intensity exposures were confirmed or revised based on follow-up telephone interviews. RESULTS: In the full assessment including all work of at least 2 weeks, 9% of cases and 4% of controls were classified as medium or high silica exposure (odds ratio of disease = 2.9; 95% confidence interval = 1.3-6.4). In contrast, only 4% of cases and 9% of controls were identified by the standardized code groups index as having worked in silica-related industries or occupations for at least 12 months, providing a much lower risk estimate for disease (0.4; 0.2-0.9). CONCLUSIONS: Specific task-based questions must be included to assess the full potential of occupational silica exposure. These findings highlight the limitations of using standardized code groups to define exposure or to select jobs for industrial hygienist review.

Gliomas and farm pesticide exposure in men: the upper midwest health study.

The National Institute for Occupational Safety and Health evaluated farm pesticide exposure and glioma risk in a study that included 457 glioma cases and 648 population-based controls, all adult men (18-80 yr old) and nonmetropolitan residents of Iowa, Michigan, Minnesota, and Wisconsin. Multiple logistic regressions were used to control for farm residence, age, age group, education, and exposure to other pesticides. No associations were found between glioma and 12 specific pesticides. We estimated adjusted odds ratios (ORs) and 95% confidence intervals (CIs) and found reduced glioma risk for insecticides (OR = 0.53, CI = 0.37-0.77), fumigants (OR = 0.57, CI = 0.34-0.95), and organochlorines (OR = 0.66, CI = 0.47-0.94). In analyses excluding proxy respondents (47% of cases) most CIs included 1.0. No positive association of farm pesticide exposure and glioma was found. Other farm exposures may explain the excess brain cancer risk seen in previous studies.

Environmental, life-style, and physical precursors of clinical Parkinson's disease: recent findings from the Honolulu-Asia Aging Study.

BACKGROUND: Increased westernization with Japanese migration to the U. S. in the early 20(th) century is thought to have altered the risk of cardiovascular disease. Whether similar effects include changes in the risk of Parkinson's disease (PD) is not clear. This report describes the relations between environmental, life-style, and physical attributes and the incidence of PD that have been observed in the Honolulu-Asia Aging Study. METHODS: Beginning in 1965, environmental, life-style, and physical attributes were recorded at selected examinations in a cohort of 8,006 Japanese-American men. Subjects were followed for clinical PD. FINDINGS: During 30 years of follow- up, PD was observed in 137 men. Overall incidence (7.1/10,000 person-years) was generally higher than in Asia and similar to rates observed in Europe and the U. S. Precursors of PD included constipation, adiposity, years worked on a sugar or pineapple plantation, years of exposure to pesticides, and exposure to sugar cane processing. Factors showing an inverse association with PD included coffee intake and cigarette smoking. Among dietary factors, carbohydrates increased the risk of PD while the intake of polyunsaturated fats appeared protective. Total caloric intake, saturated and monounsaturated fats, protein, niacin, riboflavin, beta-carotene, vitamins A, B, and C, dietary cholesterol, cobalamin, alpha-tocopherol, and pantothenic acid showed no clear relation with clinical PD. INTERPRETATION: Findings suggest that several environmental, life-style, and physical attributes appear to be precursors of PD. Whether patterns of precursors can be used to identify individuals at high risk of future PD or can broaden the scope of early interventions or recruitment into neuroprotective trials warrants further study.

Acephate exposure and decontamination on tobacco harvesters' hands.

Agricultural workers manually harvesting tobacco have the potential for high dermal fexposure to pesticides, particularly on the hands. Often gloves are not worn as it hinders the harvesters' ability to harvest the tobacco leaves. To enable harvesters to remove pesticide residue on the hands and decrease absorbed doses, the EPA Worker Protection Standard requires growers to have hand-wash stations available in the field. The purpose of this study was to measure the concentration of acephate residue on the hands of tobacco harvesters, and the effectiveness of hand washing in reducing the acephate residue. Hand-wipes from the hands of 12 tobacco harvesters were collected at the end of the morning and at the end of the afternoon over 2 consecutive days. Each harvester had one hand-wiped prior to washing his hands, and the other hand-wiped after washing his hands with soap and water. In addition to the hand-wipe samples, leaf-wipe samples were collected from 15 tobacco plants to determine the amount of acephate residue on the plants. The average acephate level in leaf-wipe samples was 1.4 ng/cm(2). The geometric mean prewash and postwash acephate levels on the hands were 10.5 and 0.4 ng/cm(2), respectively. Both prewash (P-value=0.0009) and postwash hand (P-value=0.01) samples were positively correlated with leaf-wipe concentrations. Tobacco harvester position tended to influence hand exposure. Hand washing significantly reduced acephate levels on the hand, after adjusting for sampling period, hand sampled, job position, and leaf-wipe concentration (P-value< or =0.0001) with levels reduced by 96%. A substantial amount of acephate was transferred to the hands, and while hand washing significantly reduced the amount of residue on the hands, not all residue was removed.

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. CONCLUSION: 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.