Radiographic Classification: Worker Monitoring and Surveillance
Worker monitoring is an important tool for preventing disease in occupational settings. It is considered a secondary prevention measure, intended to supplement primary prevention approaches (e.g., dust exposure monitoring and control). For the purpose of this document, it refers to using periodic chest radiography to detect pneumoconiosis in dust-exposed or potentially exposed individuals. When positive findings are identified, further medical evaluation of the affected worker may be called for, and workplace interventions that prevent disease progression in the affected individual or disease development in coworkers may be advisable. Workplace surveillance, in which a worker monitoring database is systematically examined for sentinel events and clusters of disease, provides a useful means for identifying and rectifying problems in workplace exposure control impacting groups of workers.
There is a long history of using chest radiographs in the public and private sectors in worker medical monitoring for pneumoconioses. Two examples of federal programs are the Coal Workers' Health Surveillance Program (CWHSP), which is a federal program for the detection of coal workers’ pneumoconiosis (CWP) in currently-working underground coal miners. It awards affected individuals the right to work in a reduced dust environment. Another program is the Asbestos Medical Surveillance Program (AMSP), administered by the Navy and Marine Corps Public Health Center (NMCPHC). The Occupational Safety and Health Administration (OSHA) asbestos standard requires that chest radiographs obtained for surveillance of those exposed to asbestos be interpreted and classified by a B Reader, radiologist, or physician with expertise in pneumoconioses. OSHA also specifies B Readers and the International Labour Office (ILO) Classificationin its asbestos safety and health standards for general industry, construction, and shipyard employment.
Physicians and other health care providers are encouraged, and sometimes required, to notify their State of diagnosed or suspected cases of occupational pneumoconioses, including silicosis and asbestosis. A chest radiograph classified or otherwise interpreted as consistent with the reportable disease is often considered sufficient evidence to require reporting. If physicians are not already aware of their State reporting requirements, they should contact their State to learn about any reporting requirements for which they may be responsible. Contacts for State Public Health Departments can be found on the Association for State and Territorial Health Officials (ASTHO) Web site.
Special Considerations for Classification of Chest Radiographs in Worker Monitoring and Surveillance
Worker monitoring typically involves the screening of large numbers of individuals, and hence can be costly.Therefore, use of single classifications, at some acknowledged sacrifice in reliability, may be required for a program to operate at all. However, reliance on single classifications is not a major issue because most workers are healthy, and because provisions can be made to deal with the possible limited reliability arising from reliance on single classifications. A monitoring program needs to be sensitive to detection of early disease, implying that any doubt be resolved on the side of disease detection. False positive cases are limited by undertaking further evaluation. Hence, if a possible case is identified by the initial single reading, further classifications and confirmatory studies can be subsequently applied before intervention is implemented.
In light of the above considerations, in worker health monitoring programs it is acceptable to classify films unblinded to information on the occupational history and exposures of the examinees. This may permit the reader to be sensitive as possible to the early changes that might be expected from the workplace exposures.
Use of the ILO Classification System will help maintain consistency with accepted standards of abnormality, ensure uniform standards within a program, and ensure comparability with other data.
Reader remuneration that is based on individual classification outcomes or on the overall level of reported abnormality has the obvious potential to cause bias.
Readers should be knowledgeable and experienced in the principles and practice of classification using the ILO system (e.g., B Readers).
A single classification of each radiograph is generally sufficient, particularly for radiographs that are clearly normal or abnormal. Radiographs indicating abnormality on the normal/abnormal boundary could benefit from further classification by one (or more) further readers in order to reach a more definitive conclusion on abnormality and thus improve the reliability of any resulting decisions concerning interventions.
Summarization procedures for multiple classifications should strive to be unbiased (that is, represent the central tendency within the set of multiple classifications), although in cases of doubt, they should favor the protection of workers’ health. (See the description of summarization procedures for Contested Proceedings for possible strategies that may be useful in worker monitoring.)
Knowledge of exposures and jobs worked when classifying a radiograph may be helpful in reducing uncertainty in assessing a worker’s medical status. Hence, blinding is not necessary. However, if radiographs from worker monitoring programs are to be used for epidemiologic studies of prevalence or exposure-response, it is preferable that they be re-read blinded to information that might influence a reader’s classification (e.g., industry, occupation, tenure etc) following the guidelines provided in these pages for that purpose.
Readers who are routinely engaged in classifying radiographs for monitoring programs can increase the reliability of their classifications by engaging in various forms of quality assurance. Re-classification of radiographs and comparison with past classifications can help prevent reader drift over time. Comparison of classifications from other readers or concurrent classification of calibration radiographs (specially selected radiographs that have been previously classified by expert readers) are ways to ensure that classification levels lie close to the mainstream.
It is ethically necessary to inform individual workers of findings from their individual chest radiograph. If during the course of workplace surveillance activities potential risks of occupational disease within the workplace are identified through observation of sentinel events or through tabulation of monitoring data by job, tenure, or other relevant category, ethical practice calls for workers and their employer to be informed of the identified potential risks. To further disease identification and to promote prevention, reporting of diagnosed or suspected cases of pneumoconiosis to state public health organizations is required in some states.
Use of monitoring data for population-based surveillance
Information from worker monitoring programs can be useful for population-based surveillance. For this to be effective, care must be taken to ensure that the monitoring information is representative of the population so that the prevalence statistics are valid and unbiased, and that the data are sufficiently reliable for the purpose. To achieve the latter objective, additional classifications may be necessary to improve precision. The NIOSH Coal Workers’ X-Ray Surveillance Program is a worker monitoring program that employs at least two classifications of each radiograph summarized using a standardized algorithm (42 CFR 37). Data from this program are employed in population-based surveillance and reported on the NIOSH website (see the Occupational Respiratory Disease Surveillance (ORDS) pages).
Employers should follow the OSHA asbestos standard
The OSHA asbestos standard (29 CFR 1910.1001) requires that chest radiographs obtained for surveillance of those exposed to asbestos be interpreted and classified by a B Reader, radiologist, or experienced physician with expertise in pneumoconioses. OSHA also specifies B Readers and the ILO Classification in its asbestos safety and health standards for general industry, construction, and shipyard employment.
Coal Mine Operators Should Report Silicosis and Other Pneumoconioses
The Mine Safety and Health Administration (MSHA) requires that any diagnosis of a dust disease or illness must be reported under MSHA 30 CFR 50. For purposes of reporting, MSHA considers that any miner with a history of exposure to silica or other pneumoconiosis-causing dusts and a small opacity profusion score of 1/0 or greater has illness that should be reported. The MSHA Program Policy Manual, pages 63 through 65, contains specific guidance for reporting requirements, including criteria for ILO Classification and procedures for second interpretations.
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