SILICOSIS SURVEILLANCE IN ONTARIO - DETECTION RATES, MODIFYING FACTORS, AND SCREENING INTERVALS

The Province of Ontario has had a surveillance program for workers in dusty industries for almost 70 years. This paper reports the detection rates of silicosis among 68,701 silica-exposed individuals who were f irst exposed to dust in 1950 or later, and who were still employed in 1979 or later. The detection rate varied strongly with latency, being less than two new cases per 10,000 examinations during the first two d ecades from first exposure, reaching two new cases per 1,000 examinati ons at 27 years from first exposure, and averaging between two and fou r new cases per 1,000 examinations thereafter. The silicosis incidence rate among miners was only about half that among foundry workers. Cig arette smoking was also found to be a risk factor for the diagnosis of silicosis. These data were used to model the detection rate of new ca ses of silicosis as a function of the time interval between examinatio ns, and results are presented for examination cycles between 2 and 10 years. (C) 1994 Wiley-Liss, Inc.