Distribution and Incidence
Each condition has been described among workers exposed to coal dust (CWP) and cotton dust (byssinosis). Perhaps 1 million workers worldwide are currently exposed to both coal and cotton dust.
The most reliable statistical accounts of the conditions, both contemporary and historical, are available in British and American sources. The historical and geographic incidence of each condition (and of the particular diseases defined at each time of writing) has been influenced by public policy and regulations for dust suppression, by the characteristics of the mining and manufacturing process (and, for black lung, by the type of coal itself), by the workers’ general state of health, and by their exposure to other causes of respiratory disease, notably cigarette smoke, and by the availability of publicly supported programs of disability compensation and medical care.Opinions about the distribution and incidence of the conditions have been linked to competing views about their clinical manifestations and pathology. For many years and in many communities, physicians did not differentiate the symptoms of black and brown lung from those of other common respiratory disorders. In the early stages of both diseases, workers are frequently asymptomatic and without functional impairment. For black lung defined medically as CWP, the progression of symptoms often includes chronic cough and phlegm, shortness of breath, and then functional impairment; but some workers with lesions of CWP at autopsy remained free of symptoms. The initial symptoms Ofbyssinosis are tightness in the chest, dyspnea, and a cough following a return to work after a weekend or holiday. Later symptoms extend to other workdays and include a chronic stage, with severe continuous dyspnea, chronic cough, and permanent ventilatory insufficiency.