Chapter 21: Selected occupational risk factors
Extract from the WHO publication 'Comparative Quantification of Health Risks'
Many of the 2.9 billion workers across the globe are exposed to hazardous risks at their workplaces. This chapter examines the disease and injury burden produced by selected occupational risk factors: occupational carcinogens, airborne particulates, noise, ergonomic stressors and risk factors for injuries. Owing primarily to lack of data in developing countries, we were unable to include important occupational risks for some cancers, reproductive disorders, dermatitis, infectious diseases, ischaemic heart disease, musculoskeletal disorders (MSDs) of the upper extremities, and other conditions such as workplace stress. Mesothelioma and asbestosis due to asbestos exposure, silicosis and coal workers’ pneumoconiosis are almost exclusively due to workplace exposure, but limitations in global data precluded a full analysis of these outcomes.
The economically active population (EAP) aged ≥15 years, which includes people in paid employment, the self-employed, and those who work to produce goods and services for their own household consumption, were considered the group at risk of exposure to occupational hazards. Both formal and informal sectors of employment are included in the EAP, but child labour was excluded. Exposure was quantified based on the economic sector (where people do the work) and on occupation (what people do). Our sources of data to delineate categories of exposed workers included economic databases and publications of the International Labour Organization (ILO) and the World Bank and the published scientific literature. For most risk factors the workers were grouped into high- and low-exposure categories, and the exposed population was distributed by age, sex and subregion.1 Risk estimates for the occupational hazards were obtained from the published epidemiological literature, particularly from studies of large populations, reviews and meta-analyses when available.
The occupational risk factors in our study accounted for an estimated 37% of back pain, 16% of hearing loss, 13% of chronic obstructive pulmonary disease (COPD), 11% of asthma, 8% of injuries, 9% of lung cancer and 2% of leukaemia. These work-related risks caused 775000 deaths worldwide in 2000. There were five times as many deaths in males as in females (647000 vs 128000). The leading occupational cause of death among the six risk factors was unintentional injuries (41%) followed by COPD (40%) and cancer of the trachea, bronchus or lung (13%). Workers who developed outcomes related to the occupational risk factors lost about 22 million years of healthy life. By far the main cause of years of healthy life lost (measured in disability-adjusted life years [DALYs]), within occupational diseases, was unintentional injuries with 48% of the burden. This was followed by hearing loss due to occupational noise (19%) and COPD due to occupational agents (17%). Males experienced almost five times greater loss of healthy years (DALYs) than females. Low back pain and hearing loss have in common the fact that they do not directly produce premature mortality, but they cause substantial disability and have multiple consequences for the individual and society, particularly for workers suffering the outcomes at an early age.
The major source of uncertainty in our analysis was characterizing exposure, which was based solely on economic subsectors and/or occupations and involved a large number of extrapolations and assumptions. High-quality exposure data are lacking, especially in developing countries, and European and American exposure estimates were thus applied in many instances in developing regions. This extrapolation could have substantial impact on the accuracy of analysis for the developing regions if exposures, as usually occur, vary from place to place and over time. Diseases with long latency (e.g. cancers) are more susceptible to the assumptions and extrapolations. In addition to problems produced by the length of the latency period, the magnitude of the excess risk may vary depending on the age of the person when exposure began, the duration and strength of exposure and other concomitant exposures. The turnover of workers is another issue that affects both exposure and risk assessment. Sources of uncertainty in hazard estimates (relative risk and mortality rates) include variations determined from the literature (once again caused by the use of different exposure proxies), extrapolations to regions with different working conditions, the application to females of risk measures from male cohorts, and the application of the same relative risk values to all age groups (e.g. carcinogens). Restricting the analysis to persons aged ≥15 years excludes the quantification of child labour. The exclusion of children in the estimation was due to the wide variation in the youngest age group for which countries reported economic activity rates (EARs). In addition to inconsistent data on EARs for children, there were virtually no data available on their exposure to occupational risk factors or the relative risks of such exposures. Specific, focused research on children is needed to quantify the global burden of disease due to child labour and the resulting implications.