Silicosis—Where to from here?

Australia is the first country in the world to ban the import, manufacture, supply, processing and installation of >1% crystalline silica containing engineered stone. This is a significant achievement and a result of co-operation between clinicians, researchers, peak advisory bodies and government. But the work has only just begun. We now need to turn our attention to ongoing health monitoring in at-risk workers, but also to supporting currently diagnosed workers, and preventing future epidemics. The ban was implemented in response to work which demonstrated a significant risk of silicosis and other silica associated diseases, even when control measures were in place.1 In response, next generation engineered materials are now in use, but questions around the safety of respirable dust generated from these new materials remain. For example, a recent Australian study demonstrated high levels of metals and volatile organic compounds generated from low silica content materials, which induced inflammation in the laboratory setting,2 and studies of amorphous silica or ‘quartz glass’, which has been posited as a substitute material for crystalline silica, have demonstrated comparable toxicity in vitro and in animals.3 Finally, additive polymer resins which bind and provide lustre and UV protection produce free radicals when inspired.4 Despite the introduction of these potentially safer materials, ongoing vigilance is required. Whilst recent focus has been on the engineered stone industry, workers in other industries such as construction, tunnelling and mining, remain at risk. To capture information across sectors and state boundaries, the Australian Government has recently announced the establishment of a National Occupational Respiratory Disease Registry—a repository for workplace associated lung diseases, with a diagnosis of silicosis requiring mandatory reporting.5 For this Registry to be successful, and to ensure a timely response to potential new epidemics, education and incentivization for reporting clinicians, and transparency of data use and reporting is essential.6 Government-supported screening programs have thus far detected a high proportion of affected workers with silica-associated disease.1 We need to continue to provide targeted screening programs in those previously exposed, and encourage and incentivize uptake including in those from culturally and linguistically diverse backgrounds. Current screening recommendations include the use of chest x-ray and lung function testing; however, evidence suggests chest x-ray is not sufficiently sensitive to detect early silicosis.7 CT chest is more sensitive but entails not insignificant radiation exposure. Hence research into safe, accurate, low risk and easily accessible screening tools is required. These may include novel methods such as ultra-low dose CT scans or assessment of exhaled breath samples.8 Silica exposed workers are also at greater risk of diseases other than silicosis, including chronic obstructive pulmonary disease and autoimmune disease. These conditions need to be considered in ongoing screening programs. Although often a diagnosis of silicosis is self-evident in a worker with a history of significant exposure to respirable crystalline silica, a compatible clinical picture and typical CT chest findings, there are in many cases differential diagnoses, most typically sarcoidosis and respiratory bronchiolitis interstitial lung disease, which must be considered and excluded. Diagnostic uncertainty or inaccuracy carries significant implications for the affected worker, not only in terms of their health, but also with respect to recommendations for ongoing and future work, and access to compensation, insurance or legal redress. Improved diagnostic methods, such as measuring crystal burden in bronchoalveolar lavage fluid (Figure 1),9 artificial intelligence supported image interpretation and others, may help diminish this uncertainty. Though it has been known for centuries that silicosis is caused by exposure to respirable crystalline silica, it remains a heterogeneous condition with an imperfect relationship between exposure duration and intensity, and disease. Specifically, in the engineered stone industry it has been common to see workers who have endured almost identical exposure while working side by side in the same factory for the same period of time and with the same (inadequate) respiratory protection, and yet one worker will have developed progressive massive fibrosis, whilst the other remains well with simple silicosis, or is even unaffected.1 There are clearly therefore genetic contributors to disease risk. While work has commenced to understand these genetic contributors,10 there is much still to be done. This effort will require the recruitment of many workers but is important as identifying genetic risk factors may lead to more appropriate deployment, more personalized and efficient implementation of health monitoring, and potentially even new treatments. Identified genetic risk factors may also be translatable to other interstitial lung diseases associated with occupational and environmental exposures. The natural history of artificial stone silicosis is still poorly defined, but morbidity and mortality is accelerated compared to silicosis acquired from natural stone.11 Better understanding of natural history is important so that workers and their families can be provided with more accurate information regarding prognosis, and so that the timing and nature of clinical follow-up can be more appropriately organized. This information will only be accrued through the establishment and stewardship of carefully curated disease registries. The inclusion of companion clinical samples to facilitate biomarker discovery10, 12 will assist in more accurate prognostication, aid in determining follow-up intervals and time, inform future work choices and in the future predict response to treatment. Although Australia has acted decisively compared to most of the rest of the world in addressing the epidemic of engineered stone associated silicosis, there remain thousands of young Australians, and many times more in the rest of the world, who now have a progressive lung disease with no effective treatment. These young people face a future of progressive breathlessness, eventual respiratory failure and premature death. Many may come to transplantation, but median survival after lung transplantation remains only 7 years.13 Developing effective treatments is eminently feasible in today's world of highly accelerated scientific discovery and development, with opportunities for rapid repurposing of existing therapies14, 15 but will require significant investment so that pathogenesis is intimately understood at the cell and molecular level. The concern is that these many thousands of affected workers will be forgotten as the epidemic fades, unless there is a firm commitment to safeguard ongoing investment. It has been surprising to witness the rapid resurgence of what was thought, at least in the developed world, to be a historical disease. Australia and its workers have been significantly afflicted, but has established leading programs to diagnose, manage and prevent silicosis. There is now an opportunity and responsibility to harness our region's industrial, engineering, scientific and medical expertise to consign silicosis to the history books. This work was supported by Medical Research Future Fund APP2006591: Silicosis—Harnessing new ideas to conquer the re-emergence of an ancient lung disease—The SHIELD Study. Figure was kindly provided by Dr. Simon Apte, The Prince Chares Hospital Brisbane. The authors declare no conflicts of interest.