The world health report

Chapter 4

Selected occupational risks

Throughout the world many adults, and some children, spend most waking hours at work. While at work, people face a variety of hazards almost as numerous as the different types of work, including chemicals, biological agents, physical factors, adverse ergonomic conditions, allergens, a complex causal network of safety risks, and many and varied psychosocial factors. These may produce a wide range of health outcomes, including injuries, cancer, hearing loss, and respiratory, musculoskeletal, cardiovascular, reproductive, neurotoxic, skin and psychological disorders. Because of lack of adequate global data, only selected risk factors were evaluated in this report (see Table 4.7). The disease burden from these selected occupational risks amounts to 1.5% of the global burden in terms of DALYs.

Examples of other important work-related risk factors include pesticides, heavy metals, infectious organisms, and agents causing occupational asthma and chronic obstructive lung disease. Analyses at the global level may not show the magnitude of occupational risk factors, because only the workers employed in the jobs with those risks are affected. It is important to note that not only are the affected workers at high risk, but also that workplace risks are almost entirely preventable. For example, because health care workers constitute only 0.6% of the global population, hepatitis B in this group contributes negligibly to the global burden. These workers are, however, at high risk of hepatitis B, of which 40% is produced by sharps injuries (see Box 4.4). Policies to standardize needle usage and to increase immunization coverage will prevent these infections, which represent a heavy burden in the health personnel.

Box 4.4 Sharps injuries among health care workers

Health care workers are at risk of infection with bloodborne pathogens because of occupational exposure to blood and body fluids. Most exposures are caused by "sharps" -- contaminated sharp objects, such as syringe needles, scalpels and broken glass. The three infections most commonly transmitted to health care workers are hepatitis B virus (HBV), hepatitis C virus (HCV) and human immunodeficiency virus (HIV).

Among the 35 million health care workers worldwide, about three million receive percutaneous exposures to bloodborne pathogens each year; 2 million of those to HBV, 0.9 million to HCV and 170 000 to HIV. These injuries may result in 15000 HCV, 70 000 HBV and 500 HIV infections. More than 90% of these infections occur in developing countries. Worldwide, about 40% of HBV and HCV infections and 2.5% of HIV infections in health care workers are attributable to occupational sharps exposures.

These infections are for the major part preventable, as shown by the low rates achieved in certain countries that have engaged in serious prevention efforts, including training of health care workers, HBV immunization, post-exposure prophylaxis and improved waste management. In addition to the disease burden caused to health care workers, the functioning of the health care system may be reduced because of impaired working capacity, in particular in developing countries where the proportion of health care workers in the population is already small compared with that in developed countries.

Stress at work has been shown in recent studies in industrialized nations to be associated with cardiovascular disease, but the risks will also exist in similar types of work in developing and industrializing nations. Policy-makers and decision-makers may wish to be guided by findings such as those illustrated in Box 4.5.

Box 4.5 Coronary heart disease and work-related stress

Increasing evidence from industrialized countries links coronary heart disease with work-related stress, such as high psychological demands and low decision-making latitude among white-collar occupations including managers, administrators, supervisors and proprietors. Blue-collar workers are also at risk from high work pressure and cumulative workload, in combination with low-status control.

Low job control is associated with an increase in the risk of heart disease. Shiftwork, which tends to involve heavier work, more stress, less control, and less educated workers than regular day work, also increases risk. Mechanisms of action include disturbances to the circadian rhythm, fatigue, elevated levels of serum triglycerides, and the fact that shiftwork accentuates other risk factors for heart disease.

Overall, stress-related coronary heart disease is likely to be higher in blue-collar workers when the following factors are present: restricted discretion, shiftwork (particularly at night), imbalance between efforts and rewards, high demands, a poor psychosocial work environment, social isolation, physical inactivity, or occupational violence. These risk factors may be interactive. Recent estimates for Finland indicated that a substantial proportion of ischaemic heart disease results from the combined occupational risk factors of shift work, noise, exposure to engine exhausts, and environmental tobacco smoke.

Sources: (71,72).

Work-related risk factors for injuries

Risk factors leading to injuries are present in every workplace. Industrial and agricultural workers have the highest risks, but even workers in offices, retail stores and schools are at risk(73,75). Work-related falls, motor vehicle injuries, and contact with machinery result in nearly a thousand occupational deaths every day throughout the world. Disability is another consequence of work-related injury, sometimes requiring time lost from work, and sometimes resulting in a permanent inability to return to work. Reliable data about injuries are difficult to obtain, even in industrialized countries, because of variability in insurance coverage and in accuracy of the reporting systems. Nevertheless, occupational fatality rates reported in industrializing countries are at least two to five times higher than rates reported in industrialized countries (76).

For this report, the numbers of workers at risk of injury were estimated by employment in broad occupational categories for each region, sex, and age. The corresponding fatal injury rates were obtained from an extensive literature survey. The analysis showed that overall approximately 310 000 workers lose their lives each year as a result of occupational injuries that are unintentional (from machines, motor vehicles, falls, poisonings, falling objects, fires and drowning) and intentional (homicide). Most of these deaths are preventable (77). Occupational injuries represent 0.9% of world DALYs (13.1 million) and 16% of DALYs attributable to unintentional injuries in the working population aged 15--69 years. This burden, with its heavy toll in human suffering and monetary costs, affects mainly the developing regions such as SEAR-D and WPR-B. These two regions represent almost half of the workforce of the world.

Work-related carcinogens

Many of the 150 chemical or biological agents classified as carcinogens are encountered in occupational settings (78). The risk of developing cancer is influenced by the dose received, the potency of the carcinogen, the presence of other exposures (notably tobacco smoking), and individual susceptibility. Occupational cancers are entirely preventable through elimination of exposure, using proven occupational hygiene measures such as substitution of safer materials, enclosure of processes, and ventilation.

These analyses estimated the effects of occupational exposures to numerous known carcinogens on the occurrence of respiratory and bladder cancers, leukaemia, and mesothelioma.

Globally about 20--30% of the male and 5--20% of the female working-age population (people aged 15--64 years) may have been exposed during their working lives to lung carcinogens, including asbestos, arsenic, beryllium, cadmium, chromium, diesel exhaust, nickel and silica. Worldwide, these occupational exposures account for about 10.3% of cancer of the lung, trachea and bronchus, which is the most frequent occupational cancer. About 2.4% of leukaemia is attributable to occupational exposures worldwide. In total, the attributable mortality was 146 000 (0.3%) deaths and the attributable burden was 1.4 million (0.1%) DALYs.

Work-related airborne particulates

Millions of workers in a variety of occupations, such as mining, construction and abrasive blasting, are exposed to microscopic airborne particles of silica, asbestos and coal dust (79,81). Inhalation of these particles may not only cause cancer of the lung, trachea and bronchus, but also the non-malignant respiratory diseases silicosis, asbestos and coal and pneumoconiosis ("dusty lung").

Development of these diseases is influenced by the amount of exposure and the toxicity of the dust, and the diseases are characterized by long latency periods; therefore, even in countries in which exposures have been recognized and controlled, the disease rates are only gradually declining (79). Rate trends in developing countries are mostly unknown but the magnitude of the problem is substantial (81).

Studies estimate that 5--18% of asthma may be attributable to occupational exposure, with one review study suggesting a median value of 15% for the highest quality studies. One large population study estimates that 14% of chronic obstructive pulmonary disease is attributable to occupational causes. In total, the attributable mortality for chronic obstructive pulmonary disease was 243 000 (0.4%) deaths and the attributable burden was 3.0 million (0.2%) DALYs. Several tens of thousands of additional deaths are attributable to silica, asbestos and coal dust. At the global level, the burden appears low, but the risk to workers in mining, construction and other occupations is high. For example, most workers with long-term exposure to low-to-moderate silica concentrations will develop silicosis. These diseases are entirely preventable through efforts like those of the ILO/WHO global campaign to eliminate silicosis, including elimination of exposure through substitution of safer materials, wet methods, and ventilation.

Work-related ergonomic stressors

Low back pain is associated with many ergonomic stressors at work, including lifting and carrying of heavy loads, forceful movements, demanding physical work, whole-body vibration, frequent bending, twisting, and awkward postures (82,83). The factors leading to low back pain -- physical, organizational and social factors at work, physical and social aspects of life outside the workplace, and physical and psychological characteristics of the individual -- are complex and interrelated (83). High rates of low back pain are reported for special groups of workers, such as farmers, nurses, heavy equipment operators, and construction workers (84,85). Although rarely life-threatening, low back pain causes much discomfort and can limit work, domestic and recreational activities.

Low back pain occurs frequently in industrialized countries; for example, half of all working Americans have back pain every year (86). Although data from industrializing nations are limited, the rates reported in China are similar to those in industrialized countries (87). Much low back pain can be prevented, but successful intervention requires cooperation among partners, including management, labour, industrial engineers, ergonomists, medical practitioners and the scientific research community.

This analysis suggests that about 37% of back pain is attributable to occupational risk factors. Across regions, this varies comparatively little, from between 12% and 38% for women and between 31% and 45% for men. While not a cause of mortality, low back pain causes considerable morbidity, resulting in an estimated 0.8 million DALYs (0.1%) worldwide. It is a major cause of absence from work, and therefore induces a high economic loss (84).

Work-related noise

Excess noise is one of the most common occupational hazards. Its most serious effect is irreversible hearing impairment. Noise-induced hearing loss typically begins in the frequency range of human voices, interfering with spoken communications. In the workplace, impaired communication sometimes leads to accidents. Exposure levels above 85 dB are considered to be hazardous for workers and are found especially among mining, manufacturing and construction workers, particularly in developing countries (88,89).

These analyses used the WHO definition of hearing impairment, that establishes the threshold of hearing loss at 41 dB for 500, 1000, 2000 and 4000 Hz. A 25 dB threshold of hearing loss is more generally used in the occupational setting.

Based on the WHO definition, the analysis found that about 16% of hearing loss worldwide is attributable to occupational noise exposure. This amounted to about 415000 (0.3%) DALYs. Overall, occupational noise was responsible for 4.2 million DALYs (0.3%). Noise-induced hearing loss is permanent and irreversible. It is also completely preventable. Fortunately, most occupational noise exposure can be minimized by the use of engineering controls to reduce noise at its source. A complete hearing loss prevention programme includes noise assessments, audiometric monitoring of workers' hearing, appropriate use of hearing protectors, worker education, record keeping, and programme evaluation (90).