Silicosis surveillance in Ontario from 1979 to 1992

This paper reports the detection rates of silicosis among silica-exposed persons first exposed to dust in 1950 or later and still employed in 1979 or later in the province of Ontario. The rate varied strongly with latency, being less than two new cases per 10 000 examinations during the first two decades from first exposure, reaching two new cases per 1000 examinations at 27 years from first exposure, and averaging between two and four new cases per 1000 examinations thereafter. A Poisson regression analysis found that the silicosis rate in the interval after 30 years from first exposure was more than 16 times higher than the rate prior to 20 years from first exposure. There was no significant difference in the diagnosis rates among the workers in the mining, primary metal, and nonmetallic mineral industries sectors. The rate of silicosis was higher among smokers than among never smokers (rate ratio 1.54).