Delayed Mortality Related to the Bhopal Gas Disaster, 1984-1994 Open Access

Van Meter, J. Joyous (2016)

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Background: Much has been written about the Bhopal, India gas release disaster. However, detailed information on mortality by different exposure areas, age groups, gender, and period of time have not been analyzed.

Methods: A cohort was formed by the Indian Council of Medical Research (ICMR), made up of a random sample of areas considered severely, moderately, and mildly affected (n= 25457, 33613, 18267, 15707 included in the cohort, respectively). The cohort follow-up began on Dec. 4, 1984, the day after the disaster, and continued through 1993. We calculated standardized rate ratios by area and calendar time, and used a negative binomial regression model to estimate the mortality rate ratios by age, gender, area, and calendar period, with the population at risk used as an offset. The change in mortality rates over time was also analyzed

Results: The severely affected population had the highest mortality rate (2.44 times that of the control group, CI = 2.07, 2.89), and the moderately had a lower mortality rate (1.3 times that of the control group, CI=1.11, 1.53), across all years, genders, and ages. In analyses by time period within areas, significant excess mortality was seen only in severely and moderately affected areas in December 1984 vs 1991-93 (RR=35.16 and RR 5.99 respectively) and in in 1985-86 vs 1991-93 (RR=1.68 and RR=1.25 respectively). The excess mortality was also concentrated in the youngest groups, ages 0-9. We found an estimated 516 deaths attributable to the gas disaster Dec 4, 1984 -1986 in the sampled cohort, which would represent approximately 727 excess deaths overall. However, the exact number of deaths on the day of the disaster (Dec. 3) are not known, but are likely to greatly exceed our estimated number.

Conclusion: These findings support the hypothesis that the gas disaster was largely an acute event, with the majority of the mortality occurring within days of the event. However, there was continued increased mortality into 1985-86, particularly among those 0-9 years old and in the severely affected area. We could not estimate total excess deaths due to the lack of data for the day of the disaster.

Table of Contents

Background Page 1

Methods 4

Results 6

Table 1. Selected baseline characteristics of the cohort 9

Table 2. Total population in the study 10

Figure 1. Mortality rates per 1000 males 10

Figure 2. Mortality rates per 1000 females 11

Figure 3. Mortality rate ratios from the Negative Binomial model 11

Figure 4-18. Mortality rate ratios over time 12

Discussion 19

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