Cancer downwind from sour gas refineries: the perception and the reality of an epidemic.

A rural population in southwestern Alberta, Canada, living downwind from natural gas refineries, has expressed concerns about an excess of adverse health outcomes over the last 25 years. This has escalated to the point of causing a prominent sociopolitical controversy within the province. As part of a large field epidemiologic study undertaken during the summer of 1985 to investigate possible health effects, a residential cohort study was carried out to study cancer incidence. The cohort was defined as all those individuals who resided in the area in 1970. A total of 30,175 person-years of risk within Alberta were experienced by this cohort from 1970 to 1984. The incident cancers during this period were enumerated by computerized record linkage with the Alberta Cancer Registry. Age- and sex-standardized incidence ratios, based on expected rates from three prespecified demographically similar, nonmetropolitan Southern Alberta populations, were 1.05, 1.09, and 1.03, respectively, none of which was significantly different from unity. Although they do not address the issue of etiologic association, these data can provide considerable reassurance to a community that was convinced it had experienced an epidemic of cancer.