Occupational Lung Disease and Other Respiratory Diseases
Although occupational lung diseases are often considered diseases of the industrial world, they are occurring with increased frequency in the developing world, where guidelines for worker safety are generally more lax or nonexistent. In addition, because of increased migration from rural areas to more urbanized centers and the transfer of major manufacturing activities from the developed market economy countries to the less developed countries, the number of employees with potentially harmful occupational exposures has increased exponentially in the past 30 years. The general discussion of occupation-related diseases is reviewed in chapter 60. We focus here on specific occupation-related lung diseases.
Occupational lung diseases are, for the most part, characterized as related to particular occupational exposures and generally fall into two broad pathophysiological types. One type may result in pulmonary fibrosis, which is manifested by restricted lung volume and decreased diffusion capacity on pulmonary function testing and increased interstitial pulmonary markings on chest x-ray. Certain occupational lung diseases, such as silicosis, are complicated by a substantially increased risk of tuberculosis, which contributes to the overall burden of respiratory disease in the developing world. The second pattern of occupational lung disease is that of obstructive airways disease, which may be reversible (occupational asthma) or irreversible (chronic bronchitis with or without obstruction or emphysema or COPD), in which the chest x-ray often is negative and the diagnosis is dependent largely on reported histories of exposures, symptoms, and pulmonary function testing.
There are few reliable estimates of the global burden of occupation-related respiratory diseases. Because of the lack of systematic surveillance in most developing countries, the few published estimates of occupation-related respiratory diseases have relied on selected studies involving particular industries that investigators have had unique opportunities to explore. For example, Trapido and others (1996) conducted a survey in a relatively small group of former mineworkers and found that approximately 55 percent had pneumoconiosis with or without tuberculosis. They estimated that about 25 percent of migrant and former mineworkers in South African gold mines with 15 to 25 years of exposure had occupational lung diseases. Loewenson (1999) pointed out the difficulties in making assessments of occupational risk throughout the African countries and suggested a series of methodological issues that need to be considered.
Leigh and others (1999) estimated the global burden of diseases related to occupational factors at 4.2 million to 10.0 million cases per year. If one subtracts the rates for established market economy countries, the total burden for the rest of the world is approximately 3.4 million to 9.1 million cases per year. Using limited data and applying rates from individual nations and regional groups of countries, the authors made an indirect calculation for the expected number of cases of occupation-related diseases globally. Figure 35.3 summarizes their estimates for pneumoconiosis and other chronic respiratory diseases by age and gender. Notably, these two categories of disease account for approximately 30 percent of all occupational diseases. The prevalence of these diseases increases with age and is higher among men.
[Figure
35.3]
Asbestosis and asbestos-related cancers present a particular problem in developing countries. Asbestosis can manifest both as other interstitial lung disease, as described above, and as obstructive airways disease. In addition, occupational exposure is associated with the occurrence of lung cancer, and according to studies in developed countries, the rate of occurrence is synergistically associated with smoking. Because the cost of health care compensation in the developed world exceeds the potential profit from mining and manufacturing of asbestos products, much of the industry has moved to the developing world.
LaDou (2004) has recently summarized the status of the potential for reducing occupational exposure on a worldwide basis and suggests that upward of 10 million lives will be lost if the current lack of controls and continued increases in mining and manufacturing are not changed. In 2000, more than 2 million tons of asbestos products were produced, whereas 25 years earlier the total production was 350,000 tons each year. Except for the Russian Federation and Canada, virtually all the larger producers are in the developing world, where the recognition and reporting of health effects are less well established. The likelihood of reversing this trend and developing an international ban on asbestos use is small, particularly because it is the nations that produce more asbestos products that are, in fact, increasing consumption.
The economic burden of occupational lung diseases is surprisingly difficult to document. Most developed countries and some developing countries (for example, South Africa) have legislation protecting workers from exposure and compensating those who have contracted chronic conditions. In the United States, compensation payments from the Social Security Administration and the Department of Labor for black lung disease totaled US$1.6 billion in 1996 (NIOSH 1999). Data exist on compensation for claims for various occupational lung diseases for the United States and the European Union countries. However, claims data represent only a small fraction of the true economic cost (for example, not all workers make claims; compensation payments lag considerably). For the United States, the annual costs of complying with the revised respirator standards for 1993 were US$111 million for about 5 million workers needing to use a respirator (presumably these costs of prevention were far lower than the economic cost of unprotected work) (OSHA 1998). The primary treatment for affected workers is to remove them from the inciting exposures. (See chapter 60 for discussion of preventive strategies that need to be considered to reduce the risk of occupational disease.)
Some of the other major classes of adult respiratory diseases are discussed in other chapters: tuberculosis, in chapter 16; AIDS-related lung disease, in chapter 18; and lung cancer, in chapter 29. Other diseases that have been studied, particularly in the developed world, include the hypersensitivity or immunologically related pulmonary diseases most often associated with environmental exposures to specific inhaled antigens or interstitial inflammation and fibrosis, often of unknown origin. In the developing world, little systematic work has been done on these diseases to assess incidence or prevalence. These conditions probably occur considerably less frequently than asthma and COPD. However, they are likely to have a higher prevalence in developing countries than is reported in the developed world simply because of the presumed associations with exposures to organic dusts and the increased prevalence of malnutrition (see chapter 56), both of which are likely to occur in more rural and less developed areas of the world.
See chapters 16, 18, and 29 for interventions for tuberculosis, AIDS-related lung disease, and lung cancer, respectively. Managing immunologic and fibrotic respiratory diseases with medication is extremely difficult and expensive. Therapeutic trials often fail, presumably because the treatments are not aimed at a particular antigen. The most effective way of managing these respiratory diseases is to reduce exposure to the inciting agents, an approach that hinges on two strong premises, which are not always applicable in the developed world. First, the disease must be recognized as related to a common environmental contaminant encountered in an occupational or avocational exposure—for example, exposure to thermophilic actinomycetes in moldy hay or sugarcane results in farmer's lung, and exposure to bird feathers or droppings results in bird fancier's disease. Second, community resources must be directed toward educating the public about the importance of limiting exposure to these agents.
