Characteristics of indoor and outdoor fatal hypothermia cases in Chiba, Japan

In forensic medicine, hypothermia is a frequently encountered cause of death, and this characteristic provides public health information to prevent similar deaths in the future. Previous studies revealed regional differences in hypothermia occurrence (indoors or outdoors). However, to our knowledge, no recent studies in Japan have directly compared the characteristics of indoor- and outdoor-onset cases based on forensic autopsy reports. Hence, this study aimed to determine the characteristics and risks of unexpected hypothermia-related death. It included 218 cases from the Chiba Prefecture, Japan, wherein forensic autopsies were performed and hypothermia was diagnosed; these cases were categorized into indoor- and outdoor-onset cases, and their characteristics were examined. The results showed no significant differences between the two groups in relation to the age of onset or residential environment (i.e., the presence or absence of cohabitants). The outdoor-onset group tended to have a higher incidence of dementia. Regarding the causes of hypothermia, the indoor group had more internal causes (p < 0.0001), whereas the outdoor group had more primary and external causes (p < 0.0001 and p = 0.0029, respectively). The indoor group was more undressed than the outdoor group. Atypical antipsychotic components were predominantly detected in the blood in the outdoor group (p = 0.0077). The body mass index tended to be lower in the indoor group than in the outdoor group. Broadening public awareness of the present study findings may aid in developing preventative strategies for hypothermia based on the location of onset.