An outbreak investigation of silicosis among granite carving workers in Wihan Daeng District, Saraburi Province

Abstract

The Situational Awareness Team (SAT) of the Department of Disease Control was notified by the Office of Disease Prevention and Control Region 4, Saraburi, on November 18, 2022, that two patients diagnosed with silicosis were receiving treatment at Saraburi Hospital. The outbreak investigation was later conducted on November 22, 2022, to confirm the diagnosis, identify the causes of the disease, find additional cases, assess the work environment, and establish preventive measures for silicosis. The
investigation consists of descriptive epidemiological study by reviewing patient medical records at healthcare facilities, active case finding and walkthrough survey in the workplace, and measuring silica dust levels in the workplace environment by following the National Institute for Occupational Safety and Health (NIOSH) Methods No. 7601. Data analysis was conducted using descriptive statistics. Two confirmed cases were found from the investigation. Both patients have worked as stone carvers for over 20 years and usually they are not consistently using appropriate personal protective equipment (PPE) during work. The active case finding reveled five more patients from this workplace in the past five years, all of them have died. From the walkthrough survey, there were 10 people working in the same process as confirmed cases, who had been exposed to silica dust for over five years. Half of them developed symptoms, such as chest tightness and difficulty breathing. The walkthrough survey in the workplace demonstrated that the work process like stone carving has contributed to dispersion of silica dust as confirmed by a measurement of silica dust in workplace environment, with 6 out of 8 workplace environmental samples (75%) containing silica dust levels that exceed the standard limit. Additionally, not wearing or using PPE properly was one of the main risk factors contributing to this outbreak. Reducing the dust level by engineering control, e.g. by using specialized cutting or grinding tools, water curtain, and improving ventilation, was the proper recommendation for disease control measures in this setting. Moreover, workers should also be encouraged to consistently and properly use standard PPE to reduce the risk of developing silicosis. An annual health examination based on the risks should be conducted for detection of early stages of silicosis. Lastly, assessments of silica dust levels in the workplace should be performed regularly to ensure the safety of the workplace environment.