The number of unexplained infant deaths - or cot deaths - has been falling, provisional figures from the Office of National Statistics suggest.

英国国家统计局办公室暂时性的数据显示，无法解释的婴儿死亡（摇篮病）的数量正在下降。

Placing babies on their backs has cut cot death rates

There were 264 such deaths in 2007 across England and Wales, down 7% on the year before - which itself saw a significant fall in numbers.

The rate was highest among babies born outside marriage where only the mother registered the birth.

What causes the deaths is unclear, but there are measures to reduce the risk.

These include putting a baby on its back to sleep, not smoking in the vicinity of（附近，接近） the baby and not sharing a bed if the parent is very tired or has been drinking.

The majority of deaths were among babies of a normal birthweight - 2,500 grammes or 5.5lbs and above, and occurred between 28 days and one year of age.

At a rate of 1.42 per 1,000 live births, the rate among unmarried mothers registering the birth alone was eight times that of babies born within marriage.

For births inside and outside marriage - and where the baby was registered by both parents - the death rate among parents in the routine and manual occupations was twice that among those classified as managerial or professional.

Age was also a factor: rates were highest in mothers under 20, and fell the older she became.

There were also regional variations: the North East had the highest rate, at 0.66 per 1,000 births, and the East of England the lowest, at 0.32 per 1,000.

The figures include deaths described both as sudden infant deaths and those for which the cause is "unascertained（未查明的，未弄清的）" after a full investigation¹. ONS researchers said the terms were used interchangably by coroners（验尸官，法医）.

Back to sleep

There is now suggestion that bacteria may have a role in sudden infant death, although the precise nature of any such relationship is unclear.

This has not changed the advice issued to new parents, and recently updated by the Department of Health.

"This decrease is great news and hopefully shows that we are successfully reaching parents on how to reduce the risk of cot death," said Joyce Epstein, chief executive of The Foundation for the Study of Infant Deaths.

"Nevertheless, these figures show that single mums, those under 20, are four times more likely to have a cot death than mothers over 24."

The charity is launching a new social networking site aimed at young parents next month, offering support and advice on safe sleep.