An exposure-response method for assessing the long term health effects of the bhopal gas disaster

Approximately 200,000 persons were exposed to methyl isocyanate in the Bhopal Gas leak in Bhopal, India. 4037 deaths have resulted and 30 per cent of the population are estimated to be suffering from long-term health effects. Though inflammatory damage to the eyes and lungs is the main cause of morbidity, other systems are also reported to be affected. For a disaster of this magnitude, there is a relative paucity of medical information. Very little information has been published on the late recovery period, a phase in which the detection of chronic and long-term effects is vital. Early cross-sectional studies suffer from a number of defects in study design, including validity and precision of exposure and outcome variables, selection of study and control groups, etc. By using exposure concentrations derived from Singh's analytic dispersion model, this paper outlines a strategy for doing community epidemiology in Bhopal using exposure strata for sampling. Pulmonary dose can be estimated from exposure concentration, duration and activity during exposure. For respiratory end-points, a sample size of 100/stratum will ensure study power of 90 per cent. Using multiple linear regression, data from the study can be used to build a model for prediction of lung function parameters. Exposure-stratified sampling techniques may provide valid estimates of exposure-response without including the total exposed community.