A survey of solitary death by heat stroke in Yokohama City

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.