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Editor—The recent publication by Saliet al reports “a suggestion of an increasing risk of death from non-malignant renal diseases” among rock and slag workers with employment in the early technological phase.1 No such relation was found for glass wool workers. The 1985 follow up of the man made mineral fibre worker (MMMF) study in the United States reported a significant increase in mortality for nephritis and nephrosis based on 56 deaths for the entire male cohort.2 Sali et al concluded that additional studies are warranted. We should like to point out an additional study of glass wool workers published earlier in thisJournal dealing with nephritis or nephrosis.
The Division of Occupational Health Studies, Department of Family Medicine, Georgetown University Medical Center maintains a mortality surveillance system (MSS) on behalf of Owens Corning (OC). The MSS includes both detailed exposure information and the results of an interview survey which provides information on sociodemographic factors including education, marital status, income, drinking, and smoking.3 We used a case-control study with cases and controls derived from the MSS to investigate the question of whether there is an association between exposure to respirable glass fibre or silica and mortality from nephritis or nephrosis among workers in fibrous glass wool manufacturing facilities.4
Two case-control analyses were carried out, one where the cases were defined with nephritis or nephrosis as the underlying cause and one where cases were defined as those where nephritis or nephrosis is either the underlying or a contributing cause of death.
We found no consistent relation for respirable fibres or respirable silica when the analysis was based either on underlying cause only or on underlying plus contributing cause. None of the sociodemographic variables considered suggests an increased risk when considering both underlying and contributing cause. For these data, all odds ratios for respirable fibres and silica based on both underlying and contributing cause of death are below unity with the exception of the highest exposure level for silica, which is 1.04. Although these results do not prove that there is no association between nephritis or nephrosis and exposure to fibreglass or silica in the fibreglass manufacturing environment, they do not support the assertion that such an association exists.
Boffetta and Saracci reply—Our conclusions were based on our finding on rock or slag wool workers, not on glass wool workers, a group comparable with the one studied by Chiazze et al. Indeed, we reported that we found no relation between mortality from non-malignant renal diseases and employment in glass wool production. Given that the other large study of rock or slag wool workers resulted in an increased risk from nephritis and nephrosis, we think that our pledge for additional data on possible nephrotoxicity of rock or slag wool fibres was justified.