Case-control study of mesothelioma in South Africa

Background South Africa has, uniquely, mined, transported, and used crocido lite, amosite, and chrysotile. A multicenter case-control study was done in South Africa to examine the details of asbestos exposure in cases and cont rols, and to calculate relative risks for level of certainty of asbestos ex posure, nature of exposure (e.g., environmental, occupational) and fiber ty pe. Methods Cases and controls (one cancer and one medical per case) were colle cted by six study centers from referral hospitals, and exposure information was collected by interviewing cases and controls in life. Results One hundred and twenty-three cases were accepted into the study. No ne had purely chrysotile exposure. Twenty-three cases had mined Gape crocid olite; three had mined amosite; and three Transvaal crocidolite plus amosit e. A minimum of 22 of the cases had exclusively environmental exposure, 20 were from the NW Cape crocidolite mining area. The relative risks associate d with environmental exposure in the NW Cape (crocidolite) were larger than for environmental exposure in the NE Transvaal (amosite and crocidolite): 21.9 vs. 7.1 and 50.9 vs. 12.0 for the cancer control and medical control d atasets, respectively. Conclusions The results confirm the importance of environmental exposure in the Cape crocidolite mining area, the relative paucity of cases linked to amosite, the rarity of chrysotile cases and are consistent with a fiber gra dient in mesotheliomagenic potential for South African asbestos with crocid olite > amosite > chrysotile. (C) 1999 Wiley-Liss, Inc.