Radiological progression and lung function in silicosis: a ten year follow up study

Active Surveillance of Engineered Stone Workers Facilitates Early Identification of Silicosis: A Discussion of Surveillance of Occupational Lung Diseases

Silicosis in workers exposed to respirable crystalline silica while fabricating engineered stone products is an emerging respiratory health issue. We describe silicosis in engineered stone workers in California and examine clinical features by the source of identification. Cases were identified passively using hospital-based patient discharge data or actively through outreach and medical testing following enforcement investigation. Outcomes were examined based on the source of case identification. We identified 18 cases diagnosed between 2006 and 2020. Cases identified passively compared to other identification methods were associated with lower percent predicted forced vital capacity (FVC) (P ≤ .01), forced expiratory volume in 1 s (FEV1) (P ≤ .01), and diffusing capacity of the lungs for carbon monoxide (DLCO) (P < .01) at the time of diagnosis and were more likely to be identified following death or lung transplant (P = .01). Our experience demonstrates delays in diagnosis and case identification when relying on passive surveillance methods. Enhanced public health surveillance systems can improve the early detection of occupational lung disease and inform future prevention policies.

A Descriptive Study of a Turkish Pneumoconiosis Case-Series

BACKGROUND

The study aimed to examine the conditions and factors affecting pneumoconiosis cases to determine the dimensions of the pneumoconiosis problem.

METHODS

This retrospective study was conducted in a tertiary research hospital between January 1, 2014, and December 31, 2021. Five hundred ninety-seven patients with pneumo- coniosis were included in the study.

RESULTS

Large opacities were detected in 157 cases. When we compared cases with and without Pulmonary Massive Fibrosis (PMF), age and concomitant pulmonary disease were higher in PMF cases, which also showed lower FEV1, FVC, and FEV1/FVC. PMF was more frequent in subjects with long dust exposure duration (more than 20 years) and concomitant pulmonary diseases, particularly tuberculosis. Three occupations, sandblasters, dental technicians, and ceramic workers, showed the earliest onset of pneumoconiosis.

CONCLUSIONS

The study presents pneumoconiosis data in a mixed and large population and contributes to the imple- mentation of evidence-based policies and interventions for countries like Turkey striving to cope with the problem of pneumoconiosis.

The Triple Burden of Tuberculosis, Human Immunodeficiency Virus and Silicosis among Artisanal and Small-Scale Miners in Zimbabwe

Artisanal and small-scale mining is characterized by an excessive exposure to silica-containing dust, overcrowding, poor living conditions and limited access to primary health services. This poses a risk to tuberculosis, HIV infection and silicosis. The main purpose of the study is to evaluate the burden of tuberculosis, HIV and silicosis among artisanal and small-scale miners. We conducted a cross sectional study on 3821 artisanal and small-scale miners. We found a high burden of silicosis (19%), tuberculosis (6.8%) and HIV (18%) in a relatively young population, with the mean age of 35.5 years. Men were 1.8 times more likely to be diagnosed with silicosis compared to women, adjusted prevalence ratio [aPR = 1.75 (95% CI: 1.02-2.74)]. Artisanal and small-scale miners who were living with HIV were 1.25 times more likely to be diagnosed with silicosis compared to those who were negative, [aPR = 1.25 (1.00-1.57)]. The risk of silicosis increased with both duration as a miner and severity of exposure to silica dust. The risk of tuberculosis increased with the duration as a miner. Zimbabwe is currently experiencing a high burden of TB, silicosis and HIV among artisanal and small-scale miners. Multi-sectoral and innovative interventions are required to stem this triple epidemic in Zimbabwe.

Prevalence and clinical impact of systemic autoimmune rheumatic disease in patients with silicosis

BACKGROUND

Silicosis is associated with an increased risk of developing systemic autoimmune rheumatic disease (SARD). The prognostic implications of this association are poorly characterized. The aim of this study was to determine the prevalence of SARD and autoimmune markers in a cohort of patients with exposure to silica and assess their impact on prognosis.

METHOD

We performed a prospective observational study of all patients attending the dedicated silicosis clinic of our pulmonology unit between 2009 and December 2017. Diagnosis was confirmed by a rheumatologist according to Spanish Rheumatology Society criteria. Autoimmune markers, pulmonary function tests, radiological progression, visits to the emergency department and primary care center, and hospital admissions for respiratory causes, and mortality were analyzed.

RESULTS

Overall, 489 cases of silicosis and 95 cases of exposure were studied. In total, 54 (11.0%) patients with silicosis had SARD: 12 (2.4%) rheumatoid arthritis, 10 (2.0%) systemic lupus erythematosus, 10 (2.0%) systemic sclerosis, 3 (0.6%) Sjögren syndrome, 2 (0.4%) vasculitis associated with anti-neutrophil cytoplasmic antibodies (ANCA +), 6 (1.2%) psoriatic arthritis, 3 (0.6%) ankylosing spondylitis, and 8 (1.6%) other autoimmune diseases with no special features. The patients with SARD visited the emergency room more often (63.0% vs. 42.5%; p = 0.004), and progressed more rapidly (22.2 vs. 11.7%; p = 0.030).

CONCLUSIONS

The presence of systemic rheumatic autoimmune diseases involves radiological progression and a higher clinical impact.

Prevalence and Clinical Impact of Systemic Autoimmune Rheumatic Disease in Patients with Silicosis

BACKGROUND

Silicosis is associated with an increased risk of developing systemic autoimmune rheumatic disease (SARD). The prognostic implications of this association are poorly characterized. The aim of this study was to determine the prevalence of SARD and autoimmune markers in a cohort of patients with exposure to silica and assess their impact on prognosis.

METHOD

We performed a prospective observational study of all patients attending the dedicated silicosis clinic of our pulmonology unit between 2009 and December 2017. Diagnosis was confirmed by a rheumatologist according to Spanish Rheumatology Society criteria. Autoimmune markers, pulmonary function tests, radiological progression, visits to the emergency department and primary care center, and hospital admissions for respiratory causes, and mortality were analyzed.

RESULTS

Overall, 489 cases of silicosis and 95 cases of exposure were studied. In total, 54 (11.0%) patients with silicosis had SARD: 12 (2.4%) rheumatoid arthritis, 10 (2.0%) systemic lupus erythematosus, 10 (2.0%) systemic sclerosis, 3 (0.6%) Sjögren syndrome, 2 (0.4%) vasculitis associated with anti-neutrophil cytoplasmic antibodies (ANCA +), 6 (1.2%) psoriatic arthritis, 3 (0.6%) ankylosing spondylitis, and 8 (1.6%) other autoimmune diseases with no special features. The patients with SARD visited the emergency room more often (63.0 vs. 42.5%; p = 0.004), and progressed more rapidly (22.2 vs. 11.7%; p = 0.030).

CONCLUSIONS

The presence of systemic rheumatic autoimmune diseases involves radiological progression and a higher clinical impact.

Silica-associated lung disease: An old-world exposure in modern industries

Despite silica dust exposure being one of the earliest recognized causes of lung disease, Australia, USA, Israel, Turkey and other countries around the world have recently experienced significant outbreaks of silicosis. These outbreaks have occurred in modern industries such as denim jean production, domestic benchtop fabrication and jewellery polishing, where silica has been introduced without recognition and control of the hazard. Much of our understanding of silica-related lung disease is derived from traditional occupations such as mining, whereby workers may develop slowly progressive chronic silicosis. However, workers in modern industries are developing acute and accelerated silicosis over a short period of time, due to high-intensity silica concentrations, oxidative stress from freshly fractured silica and a rapid pro-inflammatory and pro-fibrotic response. Appropriate methods of screening and diagnosis remain unclear in these workers, and a significant proportion may go on to develop respiratory failure and death. There are no current effective treatments for silicosis. For those with near fatal respiratory failure, lung transplantation remains the only option. Strategies to reduce high-intensity silica dust exposure, enforced screening programmes and the identification of new treatments are urgently required.

Silicosis prevalence and incidence among Medicare beneficiaries

INTRODUCTION

Existing epidemiologic information on silicosis relies on mortality data.

METHODS

We analyzed health insurance claims and enrollment information from 49 923 987 fee-for-service (FFS) Medicare beneficiaries aged ≥65 from 1999 to 2014. Three different definitions were developed to identify silicosis cases and results are presented as ranges of values for the three definitions.

RESULTS

Among FFS beneficiaries, 10 026-19 696 fit the silicosis case definitions (16-year prevalence: 20.1-39.5 per 100 000) with the highest prevalence among North American Natives (87.2-213.6 per 100 000) and those in New Mexico (83.9-203.4 per 100 000). The annual average prevalence had a significant (P < 0.05) 2-5% annual decline from 2005 to 2014. The average annual number of incident cases had a significant 3-16% annual decline from 2007 to 2014.

CONCLUSIONS

Silicosis is a prevalent disease among Medicare beneficiaries aged ≥65, with variation across the country. Morbidity data from health insurance claims can provide a more complete picture of silicosis burden.

Smoking cessation sharply reduced lung cancer mortality in a historical cohort of 3185 Chinese silicotic workers from 1981 to 2014

BACKGROUND

Population-based studies showed an over 50% decrease in lung cancer risk after quitting smoking for 5-6 years, but the beneficial effect in silicotics remains unknown. We aimed to rectify this knowledge gap using a large historical cohort of 3185 Chinese silicotics since 1981 and followed-up till 2014.

METHODS

Baseline information on workers' socio-demographics, smoking habits, occupational history, and medical history was collected. Smoking status was reassessed during follow-up. Multiple Cox proportional hazards model was performed to evaluate the impact of smoking cessation on lung cancer mortality.

RESULTS

Overall, 1942 deaths occurred and 188 lung cancer deaths were identified. Compared with never quitters, silicotics who were new quitters had almost halved their lung cancer risk [hazard ratio (HR) = 0.51, 95%CI: 0.34-0.76], while persistent quitters had a 53% risk reduction (HR = 0.47, 95%CI: 0.33-0.66). Lung cancer mortality approximately halved after quitting smoking for 10 years. While the risk kept decreasing with years since cessation, it did not reverse back to that of never smokers. Persistent quitters with small opacities tended to have higher beneficial effects than those with large opacities.

CONCLUSIONS

Smoking cessation for 10 years halved lung cancer mortality among silicotics, while the beneficial effect was prominent for patients with small opacities.

Subradiological silicosis

The purpose of this commentary is to bring the neglected phenomenon of subradiological silicosis and its implications to the attention of readers. We define subradiological silicosis as silicosis detectable on pathological examination of lung tissue but not visible radiologically. For extent of the phenomenon, we draw on a study using a large South African autopsy database of deceased miners and chest radiographs taken in life. At an International Labour Organization threshold of >1/0 only 43% of all pathologically detected cases were detected on chest radiograph, and only 62% of those classified on pathology as "moderate or marked" silicosis. Subradiological silicosis has a number of implications for research and practice: for dose-response studies of silicosis; for studies of the relationship between silica and conditions such as tuberculosis, lung cancer, and autoimmune disease, including the mechanistic role of fibrogenesis; for prognostication in silica exposed workers; and for workers' compensation criteria.

Radiographic progression of silicosis among Japanese tunnel workers in Kochi

OBJECTIVE

The aim of our study was to investigate the natural course of silicosis in terms of radiographic progression among Japanese tunnel workers.

METHODS

Tunnel workers with silicosis were included in our study between January 2008 and June 2011. We retrospectively assessed workers' radiographs from their first through last visits to see whether there was progression. All films were interpreted by two physicians, who had been specially trained in using the ILO (2000) International Classification of Radiographs of Pneumoconioses (ILO/ICRP). We classified the radiographic findings according to the ILO/ICRP. Survival analysis was performed and then presented as time to progression. Subgroup analysis among the progressed group was performed to demonstrate duration of progression.

RESULTS

A total of 65 patients, who were no longer exposed to silica for the duration of the study, were included. The mean age at the first visit was 58.60 ± 7.10 years. The incidence rate of progression was 42 per 1,000 person-years with a median time to progression of 17 years. Progression was demonstrated among 33 cases (51%). The mean durations of progression from category 1 to category 4 and category 2 to category 4 were 14.55 and 10.65 years, respectively. Most patients (86%) had radiographic change from category 1 or 2 directly to category 4.

CONCLUSION

Silicosis progressed at a relatively high rate among tunnel workers without further silica exposure. The high probability of progression directly from category 1 to category 4 may lead to further investigation for the improvement of disease prevention.

Progression of pneumoconiosis in coal miners after cessation of dust exposure: a longitudinal study based on periodic chest X-ray examinations in Hokkaido, Japan

BACKGROUND

The progression rate of pneumoconiosis in retired coal miners over ten years has not been studied in Japan.

METHODS

A retrospective longitudinal study was undertaken using chest X-rays of 1091 pneumoconiosis subjects in Hokkaido, Japan between 1985 and 2005.

RESULTS

The final numbers of subjects were 207 (19% of the entry) after 1 decade and 85 (8%) after 2 decades. Sixty-two percent of 207 subjects after 1 decade and 29% of 85 showed progression in 2 decades. Thirty-one percent of ILO category 1 and 55% of category 2 subjects showed progression to complicated pneumoconiosis after 1 decade, and 6% (4 of 64) of category 1 and 6% (5 of 77) of category 2 subjects progressed to complicated pneumoconiosis during 2 decades.

CONCLUSION

The progression of pneumoconiosis was observed after the cessation of dust exposure, especially during the first 10 years.

Mortality from non-malignant respiratory diseases among people with silicosis in Hong Kong: exposure-response analyses for exposure to silica dust

OBJECTIVES

To examine the exposure-response relationships between various indices of exposure to silica dust and the mortality from non-malignant respiratory diseases (NMRDs) or chronic obstructive pulmonary diseases (COPDs) among a cohort of workers with silicosis in Hong Kong.

METHODS

The concentrations of respirable silica dust were assigned to each industry and job task according to historical industrial hygiene measurements documented previously in Hong Kong. Exposure indices included cumulative dust exposure (CDE) and mean dust concentration (MDC). Penalised smoothing spline models were used as a preliminary step to detect outliers and guide further analyses. Multiple Cox's proportional hazard models were used to estimate the dust effects on the risk of mortality from NMRDs or COPDs after truncating the highest exposures.

RESULTS

371 of the 853 (43.49%) deaths occurring among 2789 workers with silicosis during 1981-99 were from NMRDs, and 101 (27.22%) NMRDs were COPDs. Multiple Cox's proportional hazard models showed that CDE (p = 0.009) and MDC (p<0.001) were significantly associated only with NMRD mortality. Subgroup analysis showed that deaths from NMRDs (p<0.01) and COPDs (p<0.05) were significantly associated with both CDE and MDC among underground caisson workers and among those ever employed in other occupations with high exposure to silica dust. No exposure-response relationship was observed for surface construction workers with low exposures. A clear upward trend for both NMRDs and COPDs mortality was found with increasing severity of radiological silicosis.

CONCLUSION

This study documented an exposure-response relationship between exposure to silica dust and the risk of death from NMRDs or COPDs among workers with silicosis, except for surface construction workers with low exposures. The risk of mortality from NMRDs increased significantly with the progression of International Labor Organization categories, independent of dust effects.

Nitric Oxide and Reactive Oxygen Species Production Causes Progressive Damage in Rats after Cessation of Silica Inhalation

Our laboratory has previously reported results from a rat silica inhalation study which determined that, even after silica exposure ended, pulmonary inflammation and damage progressed with subsequent fibrosis development. In the present study, the relationship between silica exposure, nitric oxide (NO) and reactive oxygen species (ROS) production, and the resultant pulmonary damage is investigated in this model. Rats were exposed to silica (15 mg/m3, 6 h/day) for either 20, 40, or 60 days. A portion of the rats from each exposure were sacrificed at 0 days postexposure, while another portion was maintained without further exposure for 36 days to examine recovery or progression. The major findings of this study are: (1) silica-exposed rat lungs were in a state of oxidative stress, the severity of which increased during the postexposure period, (2) silica-exposed rats had significant increase in lung NO production which increased in magnitude during the postexposure period, and (3) the presence of silica particle(s) in an alveolar macrophage (AM) was highly associated with inducible nitric oxide synthase (iNOS) protein. These data indicate that, even after silica exposure has ended, and despite declining silica lung burden, silica-induced pulmonary NO and ROS production increases, thus producing a more severe oxidative stress. A quantitative association between silica and expression of iNOS protein in AMs was also determined, which adds to our previous observation that iNOS and NO-mediated damage are associated anatomically with silica-induced pathological lesions. Future studies will be needed to determine whether the progressive oxidative stress, and iNOS activation and NO production, is a direct result of silica lung burden or a consequence of silica-induced biochemical mediators.

Peak expiratory flow and respiratory morbidity: a study among silica-exposed workers in India

BACKGROUND

The present cross-sectional study was carried out among 136 quartz stone grinders with the objective of studying the peak expiratory flow (PEF) and the associated epidemiological factors.

METHODS

Interview technique was used to record demographic characteristics and occupational history on a predesigned proforma, which included questionnaires regarding demographic, occupational and clinical characteristics. This was followed by complete medical examination and measurement of PEF using Spirovit SP-10. The study included 75 (55.1%) male and 61 (44.9%) female silica-exposed workers. The mean age of the subjects was 31.77 +/- 9.99 years whereas the mean duration of exposure was 2.74 +/- 1.65 years. The mean PEF was found to be 5.16 +/- 2.1 L/min.

RESULTS

In the present study the PEF was significantly reduced in those having respiratory morbidity on both unadjusted and adjusted analyses.

CONCLUSIONS

This suggests that along with the restrictive pathology caused by free silica dust, obstructive changes are also encountered in silica-exposed workers.

Obstructive pulmonary function defects among Taiwanese firebrick workers in a 2-year follow-up study

The purpose of the study was to follow up an earlier observation of pulmonary function among workers employed in firebrick-manufacturing factories. A 2-year follow-up study of pulmonary function among 442 workers in 30 firebrick-manufacturing factories was designed. Excluding 79 workers with a history of other occupational dust exposure, changes in pulmonary function of 291 firebrick workers were compared with pulmonary function in 72 control subjects over a period of 2 years. Baseline pulmonary function values (i.e., forced expiratory volume in 1 second [FEV1]/forced vital capacity [FVC] and forced expiratory flow after 50% of vital capacity has been expelled [FEF50%] in smoking firebrick workers, and FEV1/FVC and FEF75% in nonsmoking firebrick workers) were significantly lower than those in the comparison group. The statistical method for repeated measurements was used for comparison of the difference between follow-up and baseline lung function. There was no significant difference in FVC and FEV1 changes between firebrick workers and those in the comparison group during the 2-year follow-up period. The decreases in FEV1/FVC, peak expiratory flow rate, maximal midexpiratory flow, and FEF50% in the firebrick workers were significantly greater than in the comparison group, after adjustment for smoking status. The FEV1, maximal midexpiratory flow, FEF50%, and FEF75% also showed a dose-response relationship with job titles. The decrement of pulmonary function in the 2-year follow-up period was the worst in burning work, followed by crushing and molding. The results show that workers in firebrick-manufacturing factories with exposure to silica-containing dusts may contract obstructive pulmonary function defects.

Radiological progression and its predictive risk factors in silicosis

OBJECTIVES

To investigate the risk factors predicting radiological progression in silicosis in a prospective cohort study of patients with silicosis who were previously exposed to silica from granite dust.

METHODS

From among a total of 260 patients with silicosis contracted from granite work, 141 with available serial chest x ray films of acceptable quality taken over a period of 2 to 17 (mean 7.5) years, were selected for study. Ninety four (66.7%) had ended exposure 5 or more years previously (mean 10.1 years, maximum 28 years). Radiological progression was assessed by paired comparison of the initial and most recent radiographs, with two or more steps of increase in profusion of small opacities according to the 12 point scale of the International Labour Organisation (ILO) classification of radiographs of pneumoconiosis, taken from the majority reading by a panel of three independent readers.

RESULTS

Overall, 37% of patients with silicosis had radiological evidence of progression. From the initial radiographs, 24 (31.6%) of those with radiological profusion category 1, 15 (37.5%) of those with radiological profusion category 2, and 13 (52%) of those with complicated silicosis (including all seven with category 3 profusion of small opacities) showed radiological progression. As expected, progression was more likely to be found after longer periods of follow up (the interval between the two chest x ray films) with a 20% increased odds of progression for every additional year of follow up. After adjustment for varying intervals of follow up, the probability of radiological progression was found to be significant if large opacities were present in the initial chest x ray film. Progression was also less likely to be found among those who had ended exposure to silica longer ago, although the result was of borderline significance (p=0.07). Tuberculosis was also associated with increased likelihood of progression (borderline significance).

CONCLUSIONS

There is a high probability of radiological progression in silicosis after high levels of exposure to granite dust among workers who were followed up for up to 17 years. A significant risk factor is the extent of radiological opacities in the initial chest x ray film. The probability of progression is also likely to be reduced with longer periods after the end of exposure.

Pulmonary dysfunction in silica-exposed workers: a relationship to radiographic signs of silicosis and emphysema

BACKGROUND

It has been established that occupational exposure to silica dust may cause significant impairment of pulmonary function. To compare the contribution of silicosis and emphysema to pulmonary dysfunction, radiographic signs of silicosis and emphysema in silica exposed workers were analyzed.

METHODS

Two hundred and twenty workers exposed to silica working in a Chinese refractory plant were selected as study subjects. Their findings of silicosis and emphysematous changes on radiograph were classified and evaluated. A questionnaire on respiratory symptoms, smoking, and occupational history was administered. All the workers performed measurements of spirometry and CO single-breath diffusing capacity.

RESULTS

Radiographic hyperinflation was detected in 9% of the workers without silicosis and in 33% of the workers with silicosis. Silicosis was significantly associated with hyperinflation after adjusting for exposure duration, age, and smoking. Respiratory symptoms were more frequent in the more severe cases of silicosis. Regression analysis showed that silicosis was significantly associated with decreases in the parameters of pulmonary function, but the significance disappeared when the hyperinflation term was added to the models. Radiographic hyperinflation was strongly associated with decreases in FEV1 and FEV1/FVC while relevant factors were controlled. Comparison between workers with and without hyperinflation showed that the former had significantly lower pulmonary function values.

CONCLUSIONS

The results suggest that emphysema associated with silicosis is likely to be responsible for pulmonary obstruction and decreased diffusing capacity occurring in silica-exposed workers.

Changes in lung function of granite crushers exposed to moderately high silica concentrations: a 12 year follow up

45 granite crushers and 45 age and smoking matched referents underwent pulmonary function tests in 1976 and 1988. On average, the granite crushers at follow up had worked for 22 years, were 52 (range 36-78) years old, and had inhaled a cumulated amount of 7 mg of silica in the respirable dust fraction. Between 1976 and 1988 the average concentration of respirable quartz in air was 0.16 mg/m3 (threshold limit value (TLV) = 0.10 mg/m3). In 1988 the granite crushers had somewhat lower forced expiratory flows (forced expiratory volume in one second/vital capacity (FEV1/VC) -4.5% and forced midexpiratory flow FEF50 -15%) compared with the referents and a more uneven ventilation distribution (17% higher slope of phase III in the nitrogen single breath curve). Five smoking granite crushers, but none of the referents, had an FEV1 < 80% of the predicted. During the 12 year interval the granite crushers had--compared with the matched referents--a greater decrease in FEV1 (-4.6%), FEV1/VC (-5.4%), maximal expiratory flow, (-8%) and FEF50 (-14%), and a larger increase in phase III and static compliance (p < 0.02 in all variables). The functional changes suggest the presence of airways obstruction and increased compliance of the lungs. Exposure to silica at concentrations of about twice the present TLV was thus associated with airways obstruction and loss of elastic recoil rather than fibrosis and a restrictive function loss as seen in silicosis. The changes were on average small, but in some tobacco smokers more pronounced changes were found.