Bath-related deaths in Kagoshima,the southwest part of Japan

Introduction

Although most Japanese people relax by taking a bath, several reports have warned of sudden death in the bathroom due to natural causes. ^1–7 Those reports indicate that the mortality rate due to ‘bath-related death’ in Japan is much higher than that in the United States, and that bath-related death occurs most frequently during the cold season (winter in Japan). However, those previous reports focused their examinations on the northeast areas in Japan.

Kagoshima Prefecture is located in the southwest of Japan, and has a temperate climate (annual mean air temperature in Kagoshima city is 19.2°C). The present study investigated the cases of bath-related death that occurred in Kagoshima Prefecture in order to compare the features of bath-related death in the southwest area with those in northeast areas of Japan. Moreover, the demographic and circumstantial factors were reviewed to determine a strategy for preventing sudden death in the bathroom.

Materials and methods

All inquest records collected between 2006 and 2007 were investigated in cooperation with the First Department of Criminal Investigation of the Kagoshima Prefectural Police Headquarters. The records of sudden death in the bathroom were carefully gathered and assessed. In each case, the patients' details, including gender, age, month in which the episode occurred, location where the episode occurred, time of day when the episode occurred, a history of alcohol use, a past history of illness and the cause of death, were reviewed.

A statistical analysis was performed using the StatView software package for Windows, version 5.0. The total numbers and age-specific mortality rates were compared between men and women by using Z-test under a binomial distribution of counts. A value of P < 0.05 was considered to indicate a significant difference.

Results

In Kagoshima, there were 338 cases of bath-related death in 2006 and 2007, for a crude mortality rate of 9.7 per 100,000 persons per year. Among the 338 bath-related deaths, 174 were men and 164 were women. There was no significant difference in the total number of bath-related death between men and women (P = 0.1075). The average age of the victims was 76.6 years, ranging from 37 to 101 years, and 300 of the 338 patients (88.8%) were 65 years old and over (Figure 1). The age-specific mortality rates of bath-related death increased with age (Figure 2). Although the rates among men and women were similar in cases under 70 years of age, in cases over 80 years of age, there were significantly more men than women (80 years of age, P=0.0011; 90 years of age, P = 0.0096).

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Figure 1

Distribution of age and gender in bath-related death

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Figure 2

Crude mortality rates by age. The mortality rates were compared between men and women using Z-test under a binomial distribution of counts. **P < 0.01 men versus women

There was a clear seasonal trend in the occurrence of bath-related death (Figure 3). The greatest number of deaths occurred during the winter months (190 deaths [56.2%] in December to February), whereas the summer months (June to August) had the least number of deaths (23; 6.8%). There was no significant difference in the seasonal trend associated with gender.

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Figure 3

Incidence of bath-related death during each month

Concerning the location, 287 (84.9%) of the deaths occurred at home, followed by a spa (37; 10.9%). In the bathroom, the bathtub was the most frequent location, occurring in 294 (87.0%) cases, followed by outside the bathtub in the bathroom (38; 11.2%) and the dressing room (3; 0.8%). About 50% of the deaths occurred between 16:00 and 20:00 hours, a time when the elderly usually take a bath in Japan (Figure 4). A history of alcohol drinking before bathing was reported in 15 (4.4%) of the deaths (men 12; women 3). The incidence of a past history of illness is presented in Table 1. Fifty-six patients (16.6%) were considered to be healthy and the remaining 282 had some past history of illness, including hypertension, cardiovascular disease, diabetes mellitus and central nervous system disorder. Hypertension was the most common disease (126; 37.3%).

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Figure 4

Time of day when the patients with bath-related death took a bath

Of the cases, 125 (37.3%) of the patients lived alone and 203 (60.1%) lived with their family. In Kagoshima, there were 228,370 people who lived alone and 1,524,481 people who lived with their family. Therefore, those who lived alone had a substantially higher mortality rate of bath-related death compared with those who lived with their family (27.6 versus 6.7 patients per million, P < 0.001). In addition, the postmortem interval until discovery was compared between the two groups (Figure 5). Most patients who lived with their family (109; 79.0%) were discovered within two hours after death. On the other hand, it took at least half a day for most of those who lived alone to be discovered after death.

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Figure 5

Postmortem interval until discovery. The dark grey bars and the light grey bars indicate the postmortem interval until discovery in those who lived with their families and in those who lived alone, respectively

No medicolegal autopsies were performed in these cases of bath-related death. The cause of death was determined only by external examination. The incidence of findings that indicate drowning, such as frothy exudates from the mouth and nose, was 15.6%. Figure 6 shows that the cause of death indicated on the death certificate was heart disease in 226 (66.9%) cases, central nervous system disorder in 55 (16.3%) cases, drowning in 45 (13.3%) cases and other causes in 12 (3.6%) cases.

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Figure 6

Cause of deaths in the bathroom described in the death certificate. CNS, central nervous system

Discussion

During 2006–2007, there were 4196 inquest cases in Kagoshima Prefecture. Among them, 338 (8.1%) were cases of bath-related death. The number of bath-related deaths was approximately 1.6 times the number of automobile accidental deaths. Therefore, bath-related death in Kagoshima Prefecture may comprise a relatively large percentage of all deaths. Further, the crude mortality rate (per 100,000 population) of bath-related death in Kagoshima Prefecture was estimated to be 9.7. The rate was similar to that in Akita Prefecture, the northeast area of Japan (8.3–10.0; estimated from data of reference 6) and in other prefectures (approximately 4–9; estimated from data of reference 5).

The mortality rate of bath-related death in the United States was reported to be 0.16, ⁸ and the rate in Kagoshima Prefecture is about 61-fold higher. In addition, bath-related death in the United States occurred mainly in children less than five years old. ^8–11 In our results, the most common cause of death indicated on the death certificate was heart disease, followed by cerebrovascular disease. As previously reported, bath-related death in Japan includes characteristics of intrinsic natural death such as ischaemic heart disease and cerebrovascular disease at a higher rate than death by unnatural causes such as drowning. ^1–5 Although intrinsic natural death does occur in the bath in Western countries, the number of such deaths is small. ^12–14

Our results suggest that bath-related death may occur most frequently in the winter and in the aged group, as previously reported in other areas in Japan. ^1–7 Accordingly, it was confirmed that the cold thermal environment in winter contributes to sudden death in the bathroom, since Japanese bathrooms and anterooms are usually unheated even in winter. ¹⁵ In addition, the usual Japanese method of bathing is to immerse the body to the neck in hot water (40–42°C). Japanese people take a bath in this style almost every day. ¹⁶ Chiba et al. ⁷ reported that ventricular tachycardia, supraventricular extrasystole, ventricular extrasystole and/or a tendency of bradycardia were observed during bathing in elder volunteers who had no past history of illness. Since such arrhythmia, in particular ventricular tachycardia, can lead to ventricular fibrillation, which may trigger a fatal event, elderly people in Japan should be considered to have some undiagnosed underlying diseases for risk factor of bath-related death.

In this study, the age-specific mortality rates indicated that the rates of bath-related death in men over 80 years are significantly higher than those of women. Takasaki et al. ¹⁶ reported that 70–80% of elderly Japanese men were accustomed to bathing first, so that they might usually enter a very cold bathroom in the winter.

A history of hypertension was the most common past health issue among bath-related death in the current study. Hypertension is one of the greatest risk factors for cardiovascular mortality, and therefore cardiac events occur more frequently in people with hypertension than in healthy individuals while bathing. Furthermore, several investigations demonstrated that elderly people with hypertension often suffer a sudden decrease of blood pressure, followed by cardiopulmonary arrest. ^1,5

The current investigation showed that those cases who lived alone had a remarkably high mortality rate of bath-related death compared with cases who lived with their families. Those who live alone must take a bath every day in a cold bathroom that nobody has used prior to them. Moreover, there is no one to help those who live alone when they have serious accidents while bathing. This study showed that it took at least half a day for those who lived alone to be discovered after death. From the viewpoint of preventive medicine for bath-related death, elderly people, especially people with risk factors such as hypertension, should live with their family if possible. Even if they cannot live together, the elderly should be supervised by their neighbours and health visitors.

Our results indicate that bath-related death occurred most frequently between 16:00 and 20:00 hours, a time when elderly people usually take a bath in Japan. In addition, death occurred mostly in the home bathroom. Further, our results showed that only 4.4% of the patients had consumed alcohol prior to taking a bath, although alcohol drinking before bathing is a known risk factor for bath-related death. ^4,5 According to those results, bath-related death occurs frequently in the daily life of the elderly without alcohol drinking.

Most cases of bath-related death in Japan do not undergo postmortem examination. No autopsy was performed in any of the cases in this study. In this context, the obscurity of the diagnostic criteria of bath-related death has been suggested by several investigators. ^1,2 Therefore, it is necessary to accumulate data of objective evidence by increasing the number of cases undergoing autopsy and to establish criteria for the diagnosis of sudden death in the bathroom.

As mentioned above, the mortality rate of bath-related death in Kagoshima Prefecture, the southwest part of Japan, was not less than that in other areas of Japan. The number of bath-related deaths exceeded that of automobile deaths in Kagoshima Prefecture, as well as in other areas in Japan. ¹⁷ In addition, bath-related death should be considered common in the daily life of the elderly without alcohol drinking. Protective activities by the Japanese government and society should be developed in order to reduce the number of these tragic deaths in the bathroom.