Survival Analysis for Cohort of Bhopal Gas Disaster Victims during 1985-2015

Abstract

Context: After the gas tragedy on the night of December 2/3, 1984, at Bhopal, the Indian Council of Medical Research (ICMR) started following up on four population cohorts with different levels of post-disaster mortality from December 3-6, 1984.

Aims: The present study was undertaken to estimate the survival time of the cohort, and investigate the risk of mortality based on exposure, gender, and median age.

Settings and design: Survival analysis is generally used to evaluate factors associated with the time to an event of failure or death among any covered population.

Methods and materials: To know the cause of death and mortality rate, a retrospective cohort analysis was conducted on the outcomes of 92,320 individuals with an exposed and non-exposed group from 1985 to 2015 in Bhopal, India.

Statistical analysis used: Basic survival analysis method, Kaplan-Meier method, and Cox proportional hazard regression model were used to analyze the mortality risk.

Results: During the past 30 years, the survivability was 87.25%, and the mortality rate was 7.2% for the cohort population of Bhopal gas survivors. Cox regression analysis showed that exposed, males, and individuals above 21 years (at the time of the disaster) were at higher risk of mortality from 1985 to 2015.

Conclusions: During the initial two phases, the mortality was higher in the exposed group, but over time, their survival turned out to be the same in both groups.

Keywords: BGD victims; cohort; survival analysis.

Figure 1:

Kaplan-Meier survival curves of the BGD cohort. (a) KM- survival curves by Exposure: Exposed-Non-exposed (ref) (b) KM- survival curves by Gender: Male- Female (ref) and (c) KM- survival curves by age group: Age 21 years & above- Up to 20 years (ref)