a Department of Public Health, Tohoku University School of Medicine, Sendai, Japan.
b Department of Civil Engineering, Nagaoka College of Technology, Nagaoka, Japan.
Reprint requests to: Keiko Ogawa, Department of Public Health, Tohoku University School of Medicine, 21, Seiryo-machi, Aoba-ku, Sendai, Miyagi, 9808575, Japan. E-mail: keikoo{at}mail.cc.tohoku.ac.jp
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Abstract |
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Methods We examined the death certificates of all decedents between January 1994 and December 1996 in 16 municipalities, which covered most of the area affected by the 1995 Great Hanshin-Awaji earthquake. We analysed the extent and duration of the increased mortality from AMI. The standardized mortality ratio (SMR) of AMI was calculated weekly after the earthquake, taking the number of AMI deaths during the same period in 1994 as a reference. The main outcome measures were the number of deaths from AMI (ICD-9 410; ICD-10 I21, I22) in the study area before and after the earthquake, and the weekly SMR after the earthquake.
Results A significant increase in mortality from AMI in the study area as a whole continued for about 8 weeks after the earthquake. There was wide variation amongst the regions with respect to the extent and duration of the increased mortality from AMI. The SMR of AMI showed a positive relationship with the percentage of houses which were completely destroyed, and was almost significant (r = 0.530, P = 0.062).
Conclusions The duration of increased cardiac mortality after the 1995 Great Hanshin-Awaji earthquake was longer than seen with previous earthquakes. Further analysis to identify the factors affecting cardiac mortality is needed so that we may reduce adverse health effects during the recovery stage following natural disaster.
Keywords Acute myocardial infarction, 1995 Great Hanshin-Awaji earthquake, natural disaster
Accepted 17 December 1999
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Introduction |
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In order to analyse the characteristics of increased cardiac mortality following earthquakes, we need to observe long-term trends over one year in the affected area. Identification of the factors affecting cardiac mortality may lead us to the provision of effective prevention of the indirect long-term health effects of earthquakes.
The objectives of our study are to characterize increased cardiac mortality following the 1995 Great Hanshin-Awaji earthquake in comparison with the baseline value and to identify the factors related to increased cardiac mortality. For this purpose, we analysed the extent and the duration of increased mortality due to acute myocardial infarction (AMI) in 16 municipalities, which covered most of the area affected by the earthquake.
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Subjects and Methods |
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The study area comprised 16 municipalities; the nine districts consisted of Kobe City, five other cities (Amagasaki, Ashiya, Itami, Nishinomiya, Takarazuka) in the Hyogo prefecture and two municipalities (Sumoto and Tsuna) on Awaji island.
Table 1 shows the number of human casualties, the crude death rate, and the percentage of completely destroyed houses in each of the 16 municipalities. The total number of human casualties in the study area included more than 95% of the total number of human casualties from the 1995 Great Hanshin-Awaji Earthquake (5470/5480).
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We counted the number of deaths from AMI (ICD-9 410; ICD-10 I21, I22) in the study area at weekly intervals. We compared the values before and after the earthquake by calculating the weekly standardized mortality ratio (SMR) after the earthquake, taking the number of AMI deaths during the same period in 1994 as a reference.
In order to calculate the death rates for 1995, we obtained the population from the 1995 Population Census of Japan. Since the population census is conducted every 5 years in Japan, the population in 1994 was extrapolated from the 1985 and 1990 censuses to reduce the influence of the earthquake in 1995. The population in 1996 was calculated by modifying the method applied in Population Projections for Japan.13
The statistical significance of the SMR was analysed using the 2 test. The impact of seismic force on the human casualties and excess mortality from AMI was tested using the Pearson product-moment correlation coefficient (r) on the variables and percentage of houses that were completely destroyed. In all statistical analyses, P < 0.05 was considered statistically significant.
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Results |
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There was wide variation amongst the regions with respect to the temporary trend in increased mortality from AMI. Figures 35 show three examples; the number of deaths from AMI every 2 weeks in the Higashi-Nada, Nada and Nagata districts, Kobe City, respectively between August 1994 and July 1995. We compared the values before and after the earthquake by calculating the biweekly SMR following the disaster, taking the mean number of AMI deaths during the same period in 1994 as a reference. In Higashi-Nada (Figure 3
), sharply increased mortality was observed during the first 4 weeks following the earthquake. In Nada (Figure 4
), a significant increase continued for 8 weeks. In Nagata (Figure 5
), AMI mortality increased beyond the pre-disaster level during the first 2 weeks only.
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Table 2 shows the absolute number of AMI deaths between January and March in 1994, 1995 and 1996, and the SMR and P-values for these 3 months. A statistically-significant increase (P < 0.05) in AMI was observed in 1995 in Higashi-Nada, Nada, Hyogo, Nagata, Suma, Tarumi, Chuou, Amagasaki, Nishinomiya, Ashiya, Itami, Takarazuka and Tsuna. Nada showed the largest ratio, followed by Tsuna. There was almost no change in the number of AMI deaths in Kita between 1994 and 1995.
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Discussion |
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In this study, we observed the cardiac events for 3 years including the pre- and post-earthquake phases and covered most of the regions that received structural damage following the 1995 Great Hanshin-Awaji earthquake. More prolonged duration of increased cardiac mortality in comparison with past earthquakes was observed in the study area. A significant increase in mortality from AMI in the study area as a whole continued for about 8 weeks after the earthquake. The duration of increased mortality from AMI varied with municipality; it was 2 weeks at Nagata, 4 weeks at Higashi-Nada, 8 weeks at Nada, and about 1 year at Chuou, Amagasaki, and Itami. There was no significant relation between the duration of increased AMI mortality and the SMR of AMI. The SMR of AMI showed a positive relationship with the percentage of completely destroyed houses, and was almost significant.
There were considerable differences in the duration of cardiac mortality between the 1995 Great Hanshin-Awaji earthquake and previous earthquakes. The prolonged increase in AMI mortality can be explained by a sustained increase in the incidence of AMI. Most previous studies concluded that psychological or emotional stress at the onset of the earthquake accounted for the increased cardiac mortality. The 1995 Great Hanshin-Awaji earthquake caused a far greater number of deaths in comparison with those seen in previous earthquakes. For example, the Northridge earthquake killed 61 people, injured 7000 and left 50 000 homeless.14 The 1995 Great Hanshin-Awaji earthquake killed approximately 6000 people, injured 37 000 and left 310 000 homeless. Such a large-scale disaster is likely to cause chronic stress amongst the population during the recovery and reconstruction stage, resulting in prolonged cardiac events, although there has been no data of AMI incidence before and after the earthquake in the study area. Alternation in cardiovascular risk factors after the 1995 Great Hanshin-Awaji earthquake has been reported.15,16
Another explanation for the increased AMI mortality is the worsening of prognosis in AMI cases due to the loss or damage of hospital function. Baba reported on the loss of or damage to hospital function due to disruption of the lifeline following the 1995 Great Hanshin-Awaji earthquake.17 It was reported that in Kobe City, 103 of the 112 hospitals and 763 of the 1363 clinics suffered some damage.14 Quantitative analysis will be required to investigate the possibility that loss of hospital function caused by structural and non-structural damage after the earthquake is related to the worsening of prognosis in AMI.
Some other factors might be responsible for the increase in AMI mortality after the 1995 Great Hanshin-Awaji earthquake. For instance, socioeconomic status might influence the degree of structural damage, recovery process and access to medical care; these factors might confound the present results. Our study was solely based upon review of death certificates, in most of which verification by autopsy was not made. We therefore must admit the possibility of misclassification of cause of death during the period following the earthquake. The factors responsible for indirect health effects due to the 1995 Great Hanshin-Awaji earthquake are yet to be clarified.
In this paper, we presented the characteristics of the increased mortality from AMI following the 1995 Great Hanshin-Awaji earthquake as an indirect health effect. Unlike the direct health effects of disaster, indirect health effects are predictable and preventable. Knowledge on the factors causing indirect health effects can help us to plan appropriate resource mobilization during the recovery phase following natural disaster. Further investigation is required to clarify the factors affecting regional variation with respect to the extent and duration of increased cardiac mortality.
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Acknowledgments |
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References |
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