The occupational risk associated with asbestos exposure has been well documented. Asbestosis---parenchymal fibrosis (described in the ILO/UC Pneumoconiosis Classification as irregular opacities), pleural fibrosis, and pleural calcification---has afflicted many occupational groups exposed to these mineral fibers. Although optimistic forecasts had predicted a decline in the incidence of asbestos-induced disease. recent experience proves that the risk is still present, involving large numbers of workers in various trades. Epidemiologic studies have shown that such asbestos-exposed individuals have a significantly increased risk of death due to malignant (mesothelioma, lung, and gastrointestinal cancers ) and nonmalignant ( asbestosis ) diseases.

Asbestos pollution from industrial sources was not anticipated to pose any significant health hazard to the general public. However, Wagner's work in South Africa and Newhouse's studies in the United Kingdom suggested that the risk had already spread beyond the factory, mine, or mill gate. In 1960, Wagner et al.¹ reported mesothelioma in nonoccupationally asbestos-exposed individuals. In 1964, Newhouse et al.² reported nine cases of mesothelioma in family contacts of asbestos workers and eleven cases among individuals whose only identified asbestos exposure was associated with living within one-half mile of an asbestos factory. These initial case reports were not isolated occurrences, peculiar to only one or two regions (TABLE1). Additional reports from nine countries have brought the total number of reported cases of household mesothelioma to 37.^1-16 Thus, household asbestos contact has been established as being potentially hazardous.

Such case reports did not assess the actual incidence or extent of risk to household members or the general public, nor did they give any suggestion of the prevalence of asbestos-associated radiologic changes in such populations. We have investigated the problem in order to determine whether the potential for such disease hazard is common or rare, since such evaluation would assist in assessing measures needed for clinical surveillance and for preventive control measures.