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A survey of solitary death by heat stroke in Yokohama City

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Recent global warming and the progression of the heat-island phenomenon, mainly in urban areas, have increased the risk of heat stroke development throughout Japan. Consequently, the risk of solitary death due to heat stroke has increased, particularly in summer. Therefore, we aimed to analyze the association between some sociodemographic variables (such as age, sex, marital status) and the length of the time interval between death caused by heat stroke and discovery of the body.


We obtained the data of 69 persons who were diagnosed to have died of heat stroke during the 5 years between 2011 and 2015 in Yokohama City from vital statistics survey death certificate notifications. We also obtained emergency transportation records that matched the above-mentioned cases (48 of the 69 cases) from the Yokohama City Fire Bureau. Then, all cases (69 cases) were classified into the three groups according to the length of time from the occurrence of heat stroke death to the discovery of death (PMI-f: postmortem interval until finding). The information on each group was tabulated with regard to age (including the proportion of elderly persons), gender, marital status, and whether autopsy was performed.


The results of Cochran-Armitage trend tests among the three groups revealed that, with longer PMI-f, the proportion of elderly persons significantly decreased (p = 0.028), but the proportion of unmarried persons significantly increased (p = 0.003). Logistic regression analysis also showed that an increased likelihood of prolonged PMI-f was associated with unmarried status.


The time from the occurrence of heat stroke death to the discovery of death tended to be longer in unmarried, non-elderly persons.

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Data availability

The detailed version of the Vital Statistics Survey Death Forms of Yokohama citizens was provided from the Ministry of Health, Labour, and Welfare (MHLW), in accordance with Article 33 of the Statistics Act. The personal information of the included cases was anonymized, de-identified, and delivered to the Medical Care Bureau of Yokohama City.

The data on heat stroke from the ambulatory care information system were obtained from the Yokohama City Fire Department.



Postmortem interval until finding


Variance inflation factors


Odds ratio


Confidence interval


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We are grateful for the support and cooperation of the Yokohama City Fire Department and Medical Care Bureau, as well as Department of Biostatistics, Yokohama City University.


This work was not supported by any foundation.

Author information

Y.K., R.N., E.O., Y.K., and M.O. made substantial contributions to the conception and design of the study, gave good analysis and interpretation of the data, and assisted in drafting the article or critically revising it for important intellectual content. Y.K. and M.O. made substantial contributions to the data collection and provided materials and resources. R.N., E.O., and Y.K. made substantial contributions to the conception and design of the study, gave good analysis and interpretation of the data, and assisted in drafting the article or critically revising it for important intellectual content. All authors read and approved the final manuscript.

Correspondence to Yasuhiro Kakiuchi.

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Competing interests

The authors declare that they have no conflicts of interest with respect to this study or paper.

Ethics approval

The Ethics Committee of the Tokai University School of Medicine approved the study protocol and use of patient data (approval no. 17R-101). We also received approval from the Ethics Committee of Yokohama City Institutes of Health.

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Kakiuchi, Y., Nagao, R., Ochiai, E. et al. A survey of solitary death by heat stroke in Yokohama City. J Public Health (Berl.) (2020). https://doi.org/10.1007/s10389-020-01226-x

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  • Heat stroke
  • Solitary death
  • Marital status
  • Vital statistics
  • Emergency transportation data