Sudden death in the bathroom (bath-related death) occurs more frequently in Japan than in other countries. To clarify the epidemiological characteristics of bath-related deaths, we reviewed inquest records of deaths in Kagoshima Prefecture from 2006 to 2019. We identified 2689 cases of bath-related death. Of these cases, 90% were among people aged ≥ 65 years. The majority occurred in a home bathtub between 16:00 and 20:00. Most deaths (52.0%) occurred in winter (December–February), and there were extremely strong negative correlations with the environmental temperatures (maximum, minimum, and mean) on the day of death. We identified the environmental temperature during cold winter months that bath-related deaths are likely to occur in Kagoshima, although further investigation concerning the effects of other confounding factors is required. Forensic autopsies have only been performed in 29 cases and the cause of death was not diagnosed correctly in the majority of cases. Although autopsies are essential to elucidate the pathogenesis of the deaths, it is difficult to increase the rate of autopsies under the current Japanese death investigation system. Therefore, we suggest that the best way to prevent bath-related death is establishing an “Alert system” based on our results, and to have people refrain from bathing on dangerous days.

Sudden death in the bathroom (bath-related death) occurs more frequently in Japan than in other countries, especially among the elderly. To clarify the epidemiological characteristics of bath-related deaths, we reviewed inquest records of deaths in Kagoshima Prefecture from 2006 to 2019. We identified 2,689 cases of bath-related death. Of these cases, 90% were among people aged ≥65 years. The majority of cases occurred in a home bathtub between 16:00 and 20:00. Most deaths (52.0%) occurred in winter (December to February), and there was a significant negative correlation with the environmental temperature (maximum, minimum, and mean) on the day of death. We identified the environmental temperature that bath-related deaths were likely to occur in each region of Kagoshima. The causes of death were cardiac death in 1,231 cases and drowning in 855 cases. Forensic autopsies were performed in only 29 cases. Although autopsies are essential to elucidate the pathogenesis of bath-related deaths, it is difficult to increase the rate of autopsies under the current Japanese death investigation system. Therefore, we suggest that the best way to prevent bath-related death is establishing an “Alert system” based on our results, and to have people refrain from bathing on dangerous days.

The postmortem diagnosis of drowning death and understanding the mechanisms leading to drowning require a comprehensive judgment based on numerous morphological findings in order to determine the pathogenesis and epidemiological characteristics of the findings. Effortful breathing during the drowning process can result in intramuscular hemorrhage in respiratory and accessory respiratory muscles. However, the characteristics of this phenomenon have not been investigated. We analyzed the epidemiological characteristics of 145 cases diagnosed as drowning, in which hemorrhage, not due to trauma, was found in the respiratory muscles and accessory respiratory muscles. Hemorrhage was observed in 31.7% of these cases, and the incidence did not differ by gender or drowning location. The frequency of hemorrhage was significantly higher in months with a mean temperature below 20°C than in months above 20°C, suggesting a relationship between the occurrence of hemorrhage and low environmental temperature. Moreover, the frequency of hemorrhage was significantly higher in the elderly (aged ≥65 years) compared to those <65 years old. In the elderly, the weakening of muscles due to aging may contribute to the susceptibility for intramuscular hemorrhage. Moreover, these intramuscular hemorrhages do not need to be considered in cases of a potential bleeding tendency due to disease such as cirrhosis or medication such as anticoagulants. Our results indicate that intramuscular hemorrhage in respiratory and accessory respiratory muscles can serve as an additional criterion to differentiate between fatal drowning and other causes of death, as long as no cutaneous or subcutaneous hematomas above the muscles with hemorrhages are observed. In addition, the epidemiological features that such intramuscular hemorrhage is more common in cold environments and in the elderly may provide useful information for the differentiation.