The Burden of Silicosis in Michigan, 1988-2016.

RATIONALE: Exposure to respirable crystalline silica causes silicosis, a preventable, progressive occupational lung disease. A more rigorous occupational health standard for silica could help protect silica-exposed workers.

OBJECTIVE: Describe trends over 29 years of silicosis surveillance in Michigan.

METHODS: Michigan law requires the reporting of silicosis. We confirmed the diagnosis of silicosis of reported cases using medical questionnaires, review of medical records and chest radiographs. The Michigan Occupational Safety and Health Administration (OSHA) conducted enforcement inspections at the workplaces of the silicosis cases, including air monitoring for silica and evaluation of workplace medical surveillance programs.

RESULTS: The Michigan surveillance program identified 1048 silicosis cases from 1988-2016, which decreased from 620 during 1988-1997, to 292 during 1998-2007, to 136 during 2008- 2016. The cumulative incidence rate of silicosis decreased from 3.7 to 1.4 to 0.7 cases per 100,000 men ≥ 40 years old in Michigan over the same three periods. African-Americans had a higher cumulative incidence rate of silicosis, with 6.0 cases per 100,000 African American men ≥ 40 years in Michigan, compared to 1.2 cases per 100,000 white men ≥ 40 years in Michigan. The cases identified had severe disease; 59% have progressive massive fibrosis or category 2 or 3 small opacities per B-reading classification of the chest radiograph. Seventeen percent reported ever having active tuberculosis. On spirometry, 76% of ever and 72% of never smokers demonstrated either a restrictive or obstructive pattern. Most (65%) had not applied for workers' compensation benefits; the percentage who applied for benefits decreased from 42% to 28% to 16% over the three periods. Thirty-four of 55 (62%) workplace inspections found exposures above the new OSHA 50 µg/m3 respirable crystalline silica permissible exposure limit, and only 11% of inspected companies screened their workers for silicosis.

CONCLUSIONS: Adults with confirmed cases of silicosis have advanced disease and morbidity. Most are not using workers' compensation to pay for their care. The new OSHA silica standard, which lowers the permissible exposure limit for silica and requires medical monitoring to identify workers with silicosis, will help reduce the burden of silica exposure. It is critical for pulmonologists to be vigilant to recognize and manage this preventable occupational lung disease.