Article Text

Original research
Identification of early-stage silicosis through health screening of stone benchtop industry workers in Victoria, Australia
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  1. Ryan F Hoy,
  2. Deborah C Glass,
  3. Christina Dimitriadis,
  4. Jessy Hansen,
  5. Fiona Hore-Lacy,
  6. Malcolm R Sim
  1. School of Public Health and Preventive Medicine, Faculty of Medicine, Nursing and Health Sciences. Monash University, Melbourne, Victoria, Australia
  1. Correspondence to Dr Ryan F Hoy, School of Public Health and Preventive Medicine, Faculty of Medicine, Nursing and Health Sciences. Monash University, Melbourne, VIC 3004, Australia; ryan.hoy{at}monash.edu

Abstract

Objectives The popularity of high silica content artificial stone has been associated with emergence of severe, progressive silicosis as a major health issue affecting workers in the stone benchtop industry. This population-based health assessment programme has been implemented with the aim of identifcation of silica-associated disease at a preclinical stage.

Methods All current and former workers from the stone benchtop industry in the State of Victoria are offered free health assessments. Primary evaluations include a standardised questionnaire, physical examination, spirometry and gas transfer assessment and International Labour Organisation-categorised chest X-ray. Secondary evaluations include high-resolution CT chest, blood tests and a respiratory physician evaluation.

Results At the end of the first 12 months, 86/239 (36%) workers who had completed secondary evaluation were diagnosed with silicosis (65 simple silicosis and 21 complicated silicosis). 22 had worked in the industry for less than 10 years at the time of diagnosis. Of those with simple silicosis, 80% of workers reported breathlessness only with strenuous exercise (modified Medical Research Council score of 0), and lung function was well preserved (prebronchodilator forced vital capacity mean 99.8% predicted (SD 13.6), diffusion capacity of the lung for carbon monoxide mean 96.2% predicted (SD 18.0)). Antinuclear antibodies were detected in 37% with silicosis and 24% without silicosis.

Conclusion Early results from this comprehensive health assessment programme have indicated a high proportion of referred artificial stone benchtop workers have silicosis, including many with early-stage disease. The common finding of antinuclear antibodies suggest significant potential for autoimmune disease in this occupational group.

  • silicosis
  • occupational health practice
  • health screening

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Key messages

What is already known about this subject?

  • Artificial stone is a modern, high-silica content material which is commonly used for the fabrication of domestic kitchen benchtops. Silicosis has rapidly emerged as a major occupational health issue in this industry, with several reported cases of workers presenting with late-stage disease and requiring lung transplantation.

What are the new findings?

  • This comprehensive, population-based health assessment programme for workers in the stone benchtop industry has identified 86 workers with silicosis during the first 12 months. Seventy-six per cent were identified with early-stage, simple silicosis and 37% with detectable antinuclear antibodies.

How might this impact on policy or clinical practice in the foreseeable future?

  • This health assessment programme has already provided further insights into major health issues for workers in the stone benchtop industry. Implementation of this type of programme should be urgently considered in other regions where artificial stone material is in use. Identification of silicosis at an early stage is critical to provide an opportunity for interventions that may prevent or slow disease progression.

Introduction

Artificial stone (also referred to as engineered, composite, agglomerated or reconstituted stone and quartz conglomerate) is a composite material, typically composed of over 90% crystalline silica, mixed with pigments and bound by polymeric resin.1 2 From the early 2000s, this material has become a common choice for domestic kitchen and bathroom benchtops in many countries, including Australia. Artificial stone is promoted because of its low cost yet superior qualities to natural stone, such as greater resistance to impacts, stains and heat.3 However, if workers handling this material use high-intensity power tools without water dust suppression, they are potentially exposed to extremely high levels of respirable crystalline silica (RCS).4–6

In association with the growth in popularity of this material, the frequency of reports of silicosis affecting stone benchtop fabricators has increased alarmingly.7–10 Case series have commonly noted many workers to be young and actively employed at the time of diagnosis.1 8 10 Many cases have been identified following presentation with symptomatic disease and have been diagnosed with complicated silicosis (progressive massive fibrosis).1 8–10 The reported duration of exposure to silica from work with artificial stone appears to be relatively short, with a series from Spain noting an average of 15 years (range 5–34) at the time of diagnosis.1 Data from Israel have also noted a sevenfold excess prevalence of autoimmune disease among patients with artificial stone-associated silicosis.11

At this time, there is little knowledge of the long-term outcomes following diagnosis, but some reports indicate accelerated loss of lung function, and many affected patients have required lung transplantation.10 12 13 Studies from other industries indicate that there is a risk of silicosis progression even after cessation of silica dust exposure.14 15 The risk is greater when there is more extensive radiological disease at the time of diagnosis and there is delayed cessation of exposure.16 Considering the lack of effective treatments for silicosis, detection at the earliest possible stage is essential. Although most countries regulate health surveillance of silica-exposed workers, this has not been routinely undertaken in the artificial stone benchtop fabrication industry.10 17

Australia is one of the largest users of artificial stone, with almost half of new benchtops produced from the material.3 The Queensland State Government identified 98 workers with silicosis from the first 400 who underwent health screening, providing a preliminary insight into the potential prevalence of silicosis in the stone benchtop industry in Australia.18 In the State of Victoria (population 6.3 million), there are an estimated 200 stone benchtop fabrication businesses and at least 1400 workers currently employed. In May 2019, the Victorian Government launched an enhanced health assessment and research programme to identify stonemasons with silica-associated disease and provide diagnosed workers with appropriate support and management. The collected data are also used to support research to increase the understanding of several aspects of this emerging disease. This manuscript outlines the methodology of the health assessment programme and baseline characteristics of the initial 239 workers who have completed the secondary evaluation process.

The primary aim of the Victorian Stonemason Health Assessment and Research Programme (V-SHARP) was to provide comprehensive health assessments for all workers potentially exposed to RCS resulting from work with artificial stone in the stone benchtop industry in Victoria, Australia. Specific objectives of the programme were to

  1. Recruit and provide health assessments for all current and previous stonemasons in Victoria, with a focus on artificial stone benchtop fabricators.

  2. Provide an accurate diagnosis for stonemasons with silica-associated diseases and provide individualised clinical management.

  3. Establish baseline health data for stonemasons to assist longitudinal follow-up.

  4. Establish university-based registry databases to facilitate research.

Methods

V-SHARP is a population-based health assessment programme for current and former stonemasons, with a focus on workers in the stone benchtop industry who have been potentially exposed to hazardous levels of silica resulting from work with artificial stone (see figure 1). Health assessments are provided at no cost to the worker. Funding for the health assessment and research programme is provided by the state’s occupational health and safety regulatory agency, WorkSafe Victoria (WSV). The programme’s protocols have been developed by a multidisciplinary team, including respiratory physician, occupational physicians, radiologist, respiratory scientist and occupational hygienist. An advisory board meets periodically to review the progress of the programme. There are three components of the programme.

Figure 1

Overview of the Victorian Stonemason Health Assessment and Research Programme. ACE, angiotensin converting enzyme; DLCO, diffusion capacity of the lung for carbon monoxide; ESR, erythrocyte sedimentation rate; EUC, electrolytes, urea and creatinine; FBE, full blood examination; ILO, International Labour Organisation; LFT, liver function tests; RF, rheumatoid factor.

Primary evaluation

All current and former Victorian stonemasons are eligible to participate in the health assessment programme, regardless of duration of work in the industry. Population-based recruitment of workers is undertaken by the occupational health and safety regulatory agency (WSV). Methods used to promote the programme include targeted media campaigns, silicosis-specific educational meetings and workplace visits by inspectors. WSV operates a dedicated phone and email service for workers to register with the programme. The worker’s first contact with WSV confirms eligibility to participate in the programme, provides a registration number and an initial appointment at one of two occupational health centres (OHCs).

The primary evaluation for all workers comprises

  • Administration of a standardised questionnaire by an occupational physician, with an interpreter if required (see online supplemental file 1). Components related to the stone benchtop industry include duration of work, size of workplaces, proportion of time spent in environments with dry processing of artificial stone and dust control measures. Other components include respiratory, rheumatological and anxiety symptoms.

  • Physical examination with a focus on the respiratory system and features of autoimmune disease.

  • Chest X-ray with International Labour Organisation (ILO) classification, reported by a radiologist with National Institute for Occupational Safety and Health (NIOSH) B-Reader qualifications.

  • Respiratory function testing with assessment of spirometry and gas transfer performed at a Thoracic Society of Australia and New Zealand accredited respiratory function laboratory.

  • Consent form to provide data to the Monash University Screening Registry database (results from the screening registry will be reported separately).

Supplemental material

Primary evaluation results are assessed by the occupational physician. A ‘positive result’ is indicated by one or more of the following:

  • Significant respiratory, other symptoms or physical examination signs.

  • High or very high cumulative dose of silica exposure based on questionnaire responses.

  • Gas transfer below the lower limit of normal.

  • Spirometry pattern which is abnormal or parameters below the lower limit of normal.

  • ILO chest X-ray profusion classification of >0/1, or any other abnormality.

Results are discussed with participants by the occupational physician at a subsequent appointment. A ‘positive’ evaluation identifies participants who are at an increased likelihood of having RCS-associated disease and who require a secondary evaluation by a respiratory physician. Participants with ‘negative’ results are provided a report summarising their assessment, a letter to their employer and/or primary care physician with recommendations for ongoing, periodic health surveillance.

Secondary evaluation

The secondary evaluation comprises

  • Non-contrast high-resolution CT (HRCT) of the chest, reported by a radiologist with expertise in thoracic radiology.

  • Panel of blood tests: full blood examination, renal function, electrolyte panel, liver function tests, erythrocyte sedimentation rate, antinuclear antibodies, extractable nuclear antibodies, rheumatoid factor, ACE level and, if there is history of tuberculosis exposure or migration from a country with high prevalence of tuberculosis, interferon-gamma release assay.

  • Workers are given the opportunity to opt out of providing their secondary evaluation data to the Monash University Silica-Associated Disease Registry.

Workers are assessed by a respiratory physician with expertise in diagnosis and management of occupational and/or interstitial lung diseases and who has undergone additional silicosis education. The respiratory physician reviews investigations and questionnaire responses and undertakes a comprehensive medical assessment of the worker. The physician determines if further investigations (such as bronchoscopy) are required to confirm a diagnosis. The physician provides a report based on a standardised template (see online supplemental file 2) detailing the evaluation, and provides a diagnosis (or differential diagnosis) and a participant-specific management plan. This report is provided to the referring occupational physician, the worker and the worker’s primary care physician. If the workers must leave their place of employment, the physician may issue a worker’s compensation certificate.

Supplemental material

Silica-associated disease research registry

All workers who have attended secondary evaluation are requested via an opt-out process to consent to provide their health and exposure information to the research registry operated by the Monash University Centre for Occupational and Environmental Health. The multidisciplinary registry team includes an occupational physician, occupational hygienist, respiratory physician, epidemiologist and project manager.

Registry data are collected and managed using Research Electronic Data Capture (REDCap) electronic data capture tools hosted at Monash University.19 20 REDCap is a secure, web-based software platform designed to support data capture for research studies providing (1) an intuitive interface for validated data capture, (2) audit trails for tracking data manipulation and export procedures, (3) automated export procedures for seamless data downloads to common statistical packages and (4) procedures for data integration and interoperability with external sources. Respiratory physicians register patients and transfer data through access to a reusable web link to a REDCap questionnaire. Transferred data include the completed screening programme questionnaires, chest radiology reports, lung function test reports, respiratory physician reports and blood tests results.

The project manager assists OHCs and respiratory physicians with consenting the participants and transmission of data in a timely manner. The project manager facilitates data inputting and review of data quality.

Results

During the initial 12 months, 826 workers registered to participate in the health assessment programme (see figure 2). At the time of analysis, 239 (mean age 40.8, SD 10.7, 231 male, 96.7%) workers had completed secondary evaluation and did not opt out of sharing data with the silica-associated disease registry (baseline characteristics outlined in table 1).

Figure 2

Number of artificial stone workers at different stages of the health assessment programme after 12 months.

Table 1

Characteristics of workers (n=239) with completed secondary evaluation

Eighty-six (36%) workers referred for secondary evaluation were diagnosed with silicosis by the assessing respiratory physician based on radiological features (ILO chest X-ray and HRCT chest), occupational history and exclusion of other diagnoses. All workers diagnosed with silicosis were men with a mean age of 41.8 years (SD 9.7) and 67% were ever smokers. Sixty-five workers were diagnosed with simple silicosis (presence of pulmonary nodules consistent with silicosis, less than 10 mm diameter), and 21 were diagnosed with complicated silicosis (nodules drawn into a fibrotic mass of at least 10 mm in diameter). Twenty-three of the 65 workers with simple silicosis had an ILO chest X-ray which did not identify silicosis (ILO category 0) but were diagnosed based on consistent HRCT chest features. A total of 153 (64%) workers referred for secondary evaluation were determined to have no evidence of a current silica-associated disease, including 12 who were noted to have mediastinal and/or hilar lymphadenopathy but without parenchymal features of silicosis.

Lung function parameters were consistently lower for workers diagnosed with complicated silicosis than those with simple silicosis (table 1). Eighty per cent of workers diagnosed with simple silicosis noted breathlessness only with strenuous exercise (modified Medical Research Council (MRC) score of 0), compared with 70% with complicated silicosis.

Blood tests of workers with silicosis demonstrated elevated ACE in 41% (26/64 available results) and detectable antinuclear antibodies in 37% (25/67 available results). Thirty-two workers’ blood tests included results of the interferon-gamma release assay. Less than five indicated a positive result, suggestive of latent tuberculosis.

Of 86 workers with silicosis, 72 were currently employed in the stone benchtop industry at the time of diagnosis; the remainder were no longer working in the industry. Seventy-three workers with silicosis had a primary work location in the factory and 13 were predominately involved in onsite benchtop installation work. For workers with simple silicosis, the median duration of work in the stone benchtop industry was 14 years (range 3–33 years), compared with 13 years (range 4–28) for those with complicated silicosis.

For all workers referred for secondary evaluation, 97% indicated exposure to a work environment where dry processing of artificial stone had occurred. Forty-seven per cent had spent over half of their total work time in an environment where dry processing was occurring.

Discussion

During the first 12 months, the V-SHARP has already confirmed 86 stone benchtop industry workers have silicosis. This includes 65 workers with simple silicosis, and of significant concern are a further 21 with more radiologically advanced complicated silicosis. These 86 cases identified over a 12-month period is a dramatic increase in comparison to the average of eight silicosis compensation claims per year in Victoria for the previous 10 years.

Initial results from our study provide an insight into a systemic failure to recognise and control the risk of work with artificial stone. Ninety-seven per cent of workers referred for secondary evaluation indicated that they had spent time in an environment where water dust suppression was not used when activities such as cutting and grinding of artificial stone was undertaken. Forty-seven per cent of workers spent over half of their work time in an environment where dry processing of artificial stone was undertaken. The typical crystalline silica content of artificial stone is over 90%, and not surprisingly, dry cutting, grinding and polishing this material with high intensity power tools can generate extreme levels of RCS.2 6 A study investigating dust control measures when a handheld circular saw equipped with a diamond blade was in use noted a respirable silica dust concentration of 44.37 mg/m3 over a 30 min period.5 Although artificial stone accounted for 18% of the $105 billion global benchtop market in 2019,3 there have been few other studies investigating RCS levels associated with working with the material nor investigation of the adequacy of dust control measures.8

Half of the 86 workers diagnosed with silicosis in our study were noted to have worked in the stone benchtop industry for between 10 and 20 years, which likely reflects the introduction of artificial stone to Australia in the early 2000s and its subsequent rapid increase in popularity. Of particular concern, however, are the 22 workers with silicosis had worked in the industry for less than 10 years; this is consistent with the development of the accelerated form of silicosis. Accelerated silicosis is associated with high-intensity RCS exposure, develops over a shorter duration than chronic silicosis and is associated with disease progression even after cessation of exposure.14 15 21–23 Accelerated silicosis has been well described in other occupations where workers have been subjected to very high levels of RCS, including oilfield workers in Texas and, more recently, denim jean sandblasters in Turkey.14 22

The health assessments undertaken by V-SHARP have mostly identified workers with features of silicosis before development of significant exertional dyspnoea. Eighty per cent of workers with simple silicosis and 70% with complicated silicosis indicated no breathlessness except with strenuous exercise (modified MRC score of 0). Those with simple silicosis were noted to have well-preserved lung function at the time of diagnosis (FVC mean 99.8% predicted, diffusion capacity of the lung for carbon monoxide 96.2% predicated). The identification of workers with silicosis at an early stage of disease in this programme significantly contrasts most of the reported cases of artificial stone silicosis, which have been identified with symptomatic, if not end-stage, disease.7 9 10 13 24

The V-SHARP protocol requires an HRCT chest to be performed if any positive findings from the primary evaluation are identified, including a high or very high level of RCS exposure based on questionnaire responses (see figure 1). Twenty-three out of 65 (35%) workers have been diagnosed with simple silicosis based on HRCT chest and respiratory physician assessment, despite a normal chest X-ray (ILO grade 0) reported by a NIOSH qualified B-reader. A posterior–anterior (PA) view chest X-ray is the standard radiological technique for screening RCS-exposed workers; however, other data also question the sensitivity of this technique for workers in this industry.25 26 A retrospective review of data from the Queensland stonemason health screening programme indicated 43% (29/67) of workers with a final diagnosis of silicosis had a normal screening chest X-ray (ILO grade 0).26 An effective screening test must have high accuracy to detect disease at a preclinical stage but also needs to be affordable and available.27 Determination of the optimal imaging technique is one of many aspects of health screening of stone benchtop workers that needs to be evaluated in further detail.

These comprehensive V-SHARP assessments serve as an important baseline for workers with and without a diagnosis of silicosis. At the time of reporting, 12 workers had been identified with lymphadenopathy without parenchymal features of silicosis. So called ‘lymph node silicosis’ has previously been reported in 20% of a cohort of 264 deceased miners; however, the long-term implications of this finding in stone benchtop workers is not known. It is concerning that it may be a precursor to development of parenchymal features of silicosis.28 For workers without a current diagnosis, there is risk of development of silicosis even after cessation of RCS exposure. A Turkish study re-evaluating denim jean sandblasters 4 years after last RCS exposure noted an increase in prevalence of silicosis from 55.4% to 95.9% over that period.14 Future analysis of longitudinal assessments of these stone benchtop workers will provide valuable insights into the rate of disease progression and associated risk factors.

The association between autoimmune disease and silica exposure was recognised in the development of the V-SHARP protocol. All workers are screened for symptoms and clinical signs of autoimmune disease in the primary assessment, and workers requiring secondary assessment have blood collected for identification of autoimmune markers. Antinuclear antibodies (ANAs) have been detected in 25/67 (37%) workers with silicosis and also 29/120 (24%) stone benchtop workers without silicosis, compared with the general population rate of 9% in healthy men.29 The relevance of a positive ANA result without active symptoms of autoimmune disease is uncertain in this population; however, a study of 133 patients with lupus noted that 78% had a positive test up to 9.4 years (mean 3.3 years) prior to the onset of symptoms.30A cohort of patients with severe artificial stone silicosis referred for lung transplantation in Israel have been noted to have a sevenfold increased prevalence of autoimmune disease.11 Longitudinal assessments of stone benchtop workers will require ongoing monitoring for potential development of autoimmune disease, in addition to the respiratory effects of RCS exposure.

The descriptive results of 239 workers presented represent only a small proportion of the estimated 1400 stone benchtop workers who are eligible for assessment in Victoria. A total of 826 workers currently registered with the programme are at different stages of the protocol, limiting the data presented in this analysis. Quantitative occupational RCS exposure data are also required to better inform risk health assessments for workers in this industry. The reported frequency of dry processing artificial stone reported is extremely concerning. There is an urgent need for quantitative measurements of RCS when workers undertaking variety of tasks with artificial stone and when control measures are in place to objectively assess their potential effectiveness.

Conclusion

V-SHARP is the first described population-based, industry wide health assessment programme with input into a silica-associated disease registry. This programme is already providing valuable insights into the adverse health effects experienced by stone benchtop industry workers as a result of working with artificial stone material. All workers undergo free, protocolised assessments, which includes lung function testing and chest imaging performed in a standardised manner. As the programme continues, ongoing data collection and linkages to other health datasets, such as hospital inpatient data and cancer registry, will allow a more comprehensive understanding the long-term health of workers in the artificial stone benchtop industry. Further research will include analysis of the spectrum of radiological features of artificial stone-associated silicosis, investigation of the utility of chest X-ray compared with HRCT as a screening test, and correlation of lung function with radiological abnormalities and exposure history.

Early results from the V-SHARP further add to international concerns regarding the health of workers in the stone benchtop industry. The common practice of dry processing very high silica content artificial stone is a clear occupational hazard that has been poorly recognised to the detriment of workers’ health. Comprehensive, long-term health monitoring of all workers in this industry is necessary, as the health effects of failure to control this hazard will be experienced by these workers for many decades to come.

References

Supplementary materials

  • Supplementary Data

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Footnotes

  • Contributors RFH, DCG and MRS designed the study. RFH, DCG, CD, JH, FH-L and MRS acquired, analysed, interpreted the data and did the statistical analysis. All authors were responsible for critical revision of the manuscript for important intellectual content.

  • Funding This project was funded by WorkSafe Victoria and prepared by the Monash Centre for Occupational and Environmental Health, Monash University. The opinions, findings and conclusions expressed in this publication are those of the authors and not necessarily those of WorkSafe Victoria.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement Data are available upon reasonable request. Deidentified data are stored in a secure location and in accordance with the study protocol, and ethics approval is only accessible to research team members.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.

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