Objective: To describe state-based surveillance for silicosis that estimates prevalence of this condition, describes characteristics of affected individuals, and targets public health interventions.
Design: The data presented are a case series of patients with silicosis reported to a state health department. Patients were interviewed using a standardized questionnaire, chest radiographs interpreted by a "B-reader," pulmonary function tests obtained from medical records, and follow-back investigations conducted at the worksites where the cases had been exposed to silica.
Setting: All individuals with silicosis in the state of Michigan reported to the Michigan Department of Public Health (MDPH).
Subjects: Individuals included in this article were reported from 1987 through 1995. Cases were reported by hospitals, physicians, the state workers' compensation bureau, or from death certificates. Only data on individuals who met the criteria for silicosis developed by the National Institute for Occupational Safety and Health (NIOSH) are included.
Results: Between 1987 and 1995, 577 people were reported to MDPH who met the NIOSH criteria for silicosis. About 60% of the reports came from hospitals. The disease is occurring mainly among men born before 1940 who began working in a Michigan ferrous foundry in the 1930s or 1940s and worked there > 20 years. Over 40% of the patients are black. The overall annual average incidence rate of silicosis among black men (14.3 cases per 100,000) is seven times higher than among white men (2.1 cases per 100,000). The individuals identified with silicosis generally have severe disease. Almost 30% have progressive massive fibrosis and another 31.7% have advanced simple silicosis. Only about a third of all patients have normal results of breathing tests. Thirteen percent had been told they had tuberculosis (includes both clinical disease and a positive skin test). They have an increase of over 300% in the likelihood of dying of nonmalignant respiratory disease, both restrictive and obstructive, and an 80% increase in the likelihood of dying of lung cancer. Despite the severity of disease, over 45% of the individuals had not applied for workers' compensation. Although silicosis typically occurs after a long duration of exposure to silica, some individuals developed silicosis after a relatively short time. Three people developed silicosis who began working with silica in the 1980s, 18 in the 1970s, and 66 in the 1960s. Initial industrial hygiene follow-up inspections where the individuals had worked showed ongoing exposure above recommended and/or legal levels. Repeated inspections to these same facilities have subsequently shown reductions in silica exposure.
Conclusion: This state-based surveillance system has proved useful in characterizing individuals with silicosis, estimating its prevalence, increasing the medical community's awareness of the condition, and targeting effective public health interventions.