22 Occupational Medicine

Occupational injuries and illnesses impact substantially the health of working adults. In 2010 the U.S. Bureau of Labor Statistics (BLS) reported almost 3.1 million workplace injuries and illnesses among those employed in the U.S. private sector, an incidence rate of 3.5 cases per 100 full-time workers.¹ More than half of these were serious enough to require days away from work, job transfer, or restriction of work activities. The majority of reported cases were injuries; illnesses accounted for a smaller proportion and included respiratory and skin conditions, poisonings, hearing loss, and a broad range of other conditions. Because years of exposure are required for many diseases to develop, and because many illnesses caused by work exposures may not be recognized initially as such, annual BLS statistics probably underestimate incidence.

Estimating the frequency of work-related medical conditions is further complicated by the fact that common illnesses such as asthma, bronchitis, hypersensitivity dermatitis, cancers, and musculoskeletal disorders may be caused by workplace exposures, lifestyle factors, or a combination of both. Because clinical manifestations of such diseases are rarely specific to the exposure that caused them, recognizing occupational illness requires a detailed occupational history from the patient, often enumerating decades of workplace exposure. Such detailed occupational history is not consistently incorporated into general medical practice. Other factors that predispose to underreporting include fears among workers of job loss or reprisal, hesitation among medical practitioners to engage with the complexities of workers’ compensation insurance, and the lack of a requirement in many states for physicians to report occupational illnesses.

This chapter discusses the hazards of workplaces, the resulting injuries and illnesses, and the role of occupational medicine in assessing and preventing work-related medical conditions. A limited number of environmental exposures are described as well. Hazards can be broadly divided into those resulting from physical, chemical, biologic, and psychosocial factors. Physical hazards include direct trauma, repetitive strain, radiation, noise, and thermal stresses. Chemical hazards include organic solvents and related compounds; metals; mineral dusts such as coal, asbestos, silica and synthetic vitreous fibers; toxic gases; and a vast array of organic compounds, including pesticides and chemical-manufacturing intermediates. Biologic hazards include the blood-borne pathogens (e.g. HIV, hepatitis B and C); pathogens spread by the airborne, droplet, or contact route; pathogens spread by animal contact or arthropod vectors; and allergens. Psychosocial stressors include long hours and fatigue, limited social support, and jobs over which workers have little control.

I Physical Hazards

One need only consider the range of human activity to imagine ways in which working people may sustain acute traumatic injuries. Industrial accidents, motor vehicle crashes, falls, and trauma involving farming or mining equipment (Fig. 22-1). In general, such events are addressed immediately and directly, and the link between workplace trigger and health outcome is minimally prone to dispute. When traumas occur more gradually, as from the repetitive strain of lifting, twisting, or manipulating loads in the workplace, establishing a causal link between exposure and health condition may be more challenging. Examples include lumbar disc disease in nurses and nurses’ aides from decades of patient lifting, carpal tunnel syndrome among clerical workers, Raynaud’s disease (vasospasm resulting in reduced blood flow to fingers) in workers who use vibratory tools, and degenerative joint disease in materials handlers. Such health conditions also occur in individuals without workplace stressors, and a health care practitioner’s decision regarding work-relatedness must incorporate a thoughtful approach to the relative importance of various stressors. Generally, the receipt of workers’ compensation benefits requires that a physician state the condition “more probably than not” (>50%) is related to the workplace.

Figure 22-1 Mining tunnel cave-in.
Underground mining has one of the highest fatal injury rates of any U.S. industry—more than five times the national average compared with other industries. Between 1999 and 2008, almost 40% of all underground fatalities were attributed to mine roof, rib, and face falls.

(From http://www.cdc.gov/niosh/mining/topics/images/rockfall.jpg.)

A Radiation

As a physical hazard, radiation exposure is widespread, and occupations account for only a small portion of overall population exposures, most of which emanate from radon gas in homes, cosmic rays from the sun, and radioactive elements in the earth’s crust. The largest occupational group monitored for radiation is health care workers, although for most, exposures do not exceed typical background levels. Other exposed groups include aircraft pilots and crews, nuclear industry workers, and miners.

Individuals exposed to extremely high levels of radiation, such as in a nuclear accident, may suffer acute radiation sickness with sloughing of the skin, damage and depression of bone marrow, ulceration and bleeding in the gastrointestinal tract, inflammation and scarring of the lungs, and a range of other effects. Survivors of very high acute radiation doses also have elevated risk of blood and solid-organ malignancies. More common radiation exposures may also result in elevated cancer risk; radon exposure in miners is strongly associated with increased risk of lung cancer, and nuclear workers have shown increased rates of leukemia and lung cancer.

B Noise

Noise is one of the most prevalent physical hazards in workplaces. More than 10 million U.S. workers may be exposed to greater than 80 decibels (dB), and more than 1 million have occupational hearing loss. By age 50, an estimated half of heavily exposed construction workers and 90% of heavily exposed miners will have hearing impairment. Substantial noise exposure occurs in almost every variety of manufacturing; exposures in mining, construction, and transportation may be equally hazardous. The U.S. Occupational Safety and Health Administration (OSHA) requires periodic monitoring of noise levels and periodic audiometry of workers with exposure of 85 dB or higher.² Control of noise in the workplace often involves a combination of engineering solutions to reduce noise sources, limiting exposure time in noise environments, and wearing hearing protection.

C Heat and Cold

Thermal stress constitutes another physical stressor in workplaces. Excessive levels of heat are encountered in foundries, smelting operations, firefighting, and in many outdoor settings. Heavy work demands, heavy clothing, lack of air circulation, and high humidity may contribute to heat stress. Health effects may include lightheadedness, swelling of the extremities, muscle cramping, and in more severe cases, agitation and delirium, lysing of muscle cells, circulatory collapse, and kidney failure. Workers not accustomed to high-heat environments and those with other medical conditions are at particular risk.

Excessive cold exposure occurs among workers in cold-climate outdoor activities, divers and others in the maritime industry, military personnel, and workers in refrigerated environments. Although the potential for hypothermia, defined as a fall in body temperature to below 35° C (95° F), exists in such settings, localized cold effects are more common, such as frostbite, Raynaud’s phenomenon, and cold-induced hives.

Cold exposure may also occur in high-altitude environments, although the principal hazard of such settings is reduced oxygen content. High altitude–associated conditions range from acute mountain sickness (AMS) to potentially life-threatening pulmonary and cerebral edema. AMS is characterized by fatigue, malaise, shortness of breath, disturbances of memory, concentration and sleep, and generally occurs within 24 hours of arrival at altitude. Pulmonary edema may be triggered by changes in the pulmonary blood vessels from decreased oxygen, rapid breathing, and the resulting alkalosis and pulmonary hypertension. Edema of the brain may result from hypoxia and may be both insidious and life threatening. Gradual ascent may prevent or moderate altitude-associated illnesses.

II Chemical Hazards

More than 80,000 chemicals are in common use. Although discussion of acute and chronic toxicities is beyond the scope of this chapter, categories of particular interest, due to high frequency of use or significant health impact, are solvents, metals, mineral dusts, polycyclic aromatic hydrocarbons, pesticides, and inorganic gases. Dedicated OSHA standards exist for only a few chemical exposures. For many others, guidance is in place from the National Institute for Occupational Safety and Health (NIOSH), American Conference of Governmental Industrial Hygienists (ACGIH), and other advisory groups. In the absence of a specific standard, OSHA may cite workplaces under the General Duty Clause, which requires employers to provide a workplace free of recognized hazards.

A Solvents

Solvents are widely used in industrial processes. Major classes include aliphatic, aromatic, and halogenated compounds, all of which can cause acute encephalopathic effects, generally manifested by a sense of lightheadedness, disorientation, and irritability. Exposure occurs primarily by inhalation and skin absorption. Although symptoms generally resolve within hours following cessation of exposure, chronic encephalopathic changes, potentially with progression to dementia, may occur after years of heavy exposure. Most solvents may also irritate the skin, cause defatting of dermal tissue, and serve as carriers through the skin of other chemical substances. The following solvents have uniquely toxic properties:

 Both n-hexane and methyl-n-butyl ketone may cause a mixed motor and sensory neuropathy.

 Benzene is well established as a cause of aplastic anemia and acute myelogenous leukemia.

 Carbon tetrachloride is a potent toxin of the liver.

 Methylene chloride causes carboxyhemoglobinemia

 Carbon disulfide may cause acute psychosis, optic neuritis, peripheral neuropathy, and over time, atherosclerosis.

 Extremely heavy exposure to halogenated solvents has been associated with cardiac arrhythmias and sudden death.

Acute encephalopathic effects may result from exposure to a single solvent or a combination of solvents. Assessment of workplace exposure must consider the possibility of combined toxicity, and that measured air levels may not adequately account for dermal exposures. Biologic monitoring, generally the measurement of urinary solvent metabolites, has been used to account for body burden from different exposure pathways.

B Metals and Mineral Dusts

Metal exposures occur in a variety of industrial settings and may trigger a broad range of health effects. Although lead exposure to the general population has been greatly reduced by the removal of lead as a gasoline additive in the 1970s, many occupational groups remain at high exposure risk, including construction workers, welders, solderers, pipe cutters, foundry workers, demolition workers, home renovators, and battery makers. Toxicities associated with lead exposure range from subtle behavioral and cognitive effects to hemolytic anemia, peripheral neuropathy, chronic encephalopathy, hypertension, and impotence (Fig. 22-2). The following metals also may cause a variety of acute and chronic effects:

 Arsenic exposure causes hyperpigmented skin lesions, peripheral neuropathy, and peripheral vascular disease and is a well-established risk factor for skin and lung cancer.

 Chronic exposure to mercury is linked to tremor, psychological disturbances, and neuropathy, whereas acute exposure may trigger a severe chemical pneumonitis.

 Beryllium may also cause acute pneumonitis and in certain individuals leads to chronic berylliosis, a syndrome similar to sarcoidosis, a systemic disorder often resulting in chronic lung disease.

 Cobalt and cadmium may also affect the lungs. Cobalt causes asthma, giant cell pneumonitis, and scarring of the lungs of certain individuals; acute cadmium exposure is associated with pneumonitis. Cadmium may also severely damage the kidneys.

 Chromium and nickel have a number of skin effects and are risk factors for lung cancer.

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