• drowning
• Japanese children

Drowning, once by far the most important external cause of child deaths in Japan,¹ has reduced more rapidly than other injuries. Drowning mortality of children aged 1–4 years decreased from 45.4 per 100 000 in 1955, 4.5 times higher than that of traffic injuries, to 1.6 per 100 000 (ranking next to traffic injuries) in 2000. We could have achieved this by two main approaches: (1) environmental modification to reduce exposure to open water where most outdoor drownings occur² and (2) health education to reduce risk of bathtub drowning, which causes most of the domestic drownings.^2,3

To know how these approaches contributed to the mortality reduction, we separately examined the trends of outdoor and domestic drowning mortality among children aged 1–4 years.

Data on drowning deaths were obtained from Vital Statistics compiled by the Ministry of Health, Welfare, and Labour. Drowning was classified as E code 910 in the eighth and ninth revision of the International Classification of Diseases (ICD-8 and 9) for the period 1967–94 and classified as code W65-74 in the 10th revision (ICD-10) for the period 1995–2001.

Population data, denominators of mortality rates, were from the national censuses for the years 1970, 1975, 1980, 1985, 1990, 1995, and 2000; and from the population estimations compiled by the Ministry of Public Management, Home Affairs, Posts and Telecommunications (MPHPT) for other years. Data on the proportion of houses equipped with a bathroom were from the Housing and Land survey by MPHPT. We analyzed the trends using Poisson regression.

Until the mid-1970s, domestic drowning mortality among children aged 1–4 years did not change whereas their outside mortality declined steadily (fig 1). Consequently, outdoor mortality, three times higher than domestic mortality in the late 1960s, became lower in the late 1980s. Annual change of domestic drowning mortality after 1975 was −5.6% (95% confidence interval (CI) −5.8 to −4.9%) and that of outdoor drowning mortality was −9.1% (95% CI −9.5 to −8.6%). The proportion of households with a bathroom, 65.6% in 1968, increased rapidly in the 1970s reaching 82.8% in 1978; it increased slowly thereafter reaching 95.4% in 1998.

A difference in risk reduction between outside and inside environments is a possible explanation of the different trends. Children’s exposure to open water was reduced mainly through passive protections accompanying urbanization, such as fencing or covering rivers, ponds, lakes, and ditches.² Population shifts from rural to urban areas, and shift of children’s play from outside to inside⁴ might also have contributed to the exposure reduction.

In contrast, exposure control at home depends mostly on educational approaches that require vigilance or behavior change, such as continuous child supervision, emptying the bathtub, and locking the bathroom (children frequently drown when unattended in bathtub water reserved for laundry use.)^3,5 However, changes in customary behaviors are slow; short lapses of supervision are usual; and lock installation is uncommon.⁵ Further, the rapid increase of domestic bathrooms, especially in the 1960s and 1970s, might have increased exposure as most bathrooms in Japan are equipped with a bathtub.

If improvement in medical or pre-hospital care contributed to the mortality reduction, it would not bring more benefit to outdoor drowning. Outdoor drowning involves longer rescue time and transportation to hospital. A hospital based study in Japan indicated higher case fatality of child drowning in ditches or ponds.⁶

Although the mortality reduction at home was quite good, further reduction would be possible with other passive measures like lock installation on bathroom doors. This will decrease children’s exposure to risk at home just as fencing does around domestic swimming pools.⁷ However, legislative measures will be needed because one of the main reasons for not installing locks is living in rented property and the difficulty of getting permission for installation from the owner.⁵

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Figure 1

Drowning mortality rate (per 100 000 persons) of children aged 1–4 in Japan, 1967–2001; proportion of households with bathroom.