A CLUSTER OF BRAIN-TUMORS IN A NEW-SOUTH-WALES COLLIERY - A PROBLEM IN INTERPRETATION

Following the reporting of a cluster of cases of brain tumour in the w orkforce of an underground coal mine (Mine A) in the Newcastle coalfie ld, a study was carried out to determine whether this phenomenon was d ue to chance alone or whether an environmental cause could be postulat ed. The study design was a historical cohort study over 15 years compa ring the incidence of brain tumour (ICD9 191 and 192) in the index min e with that in two control mines (Mines B and C) in the same area and with that in the general Australian population. We compared environmen tal exposures (ionising and nonionising radiation and chemical exposur e) in the three mines. With Australian brain tumour incidence rates as reference, the standardised incidence ratio for brain tumour in Mine A was 5.3 (95 per cent confidence interval (CI) 1.08 to 14.04) and in Mines B and C combined was 1.23 (CI 0.02 to 3.80). On most environment al assessments the three mines were similar but Mine A used larger vol umes of solvents than the other mines. This study poses two questions: was the increase in cases of brain tumour in Mine A 'real' and if so, was it related to the use of solvents? Data, from an investigation of a cluster such as this, are unlikely to be conclusive. Nevertheless, such answers are demanded not only by those at risk but also by the mi ne management, which is responsible for a safe working environment. So me of the difficulties involved with this judgment are discussed.