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Media Release

June 29 2006

Strange trends in the SIDS mystery

While the death toll from SIDS has reduced by 70 per cent in the last ten years, the mystery condition is still the largest cause of death in infants between one month to one year in Australia.

Professor Adrian Esterman, an epidemiologist from UniSA’s School of Nursing and Midwifery, explains why SIDS is such a perplexing phenomenon in modern epidemiology.

“SIDS is unusual in that it is not really a cause of death. In fact it’s any death of an infant for which you can’t find a cause of death. It could be a number of things, we just don’t know,” Prof Esterman said.

“Researchers have proposed various theories including infection, heart problems, or being smothered. However, it is still a mystery.

“We’ve seen a significant reduction in SIDS since the early 1990s, largely because people have been educated about the importance of babies sleeping on their backs. It is now accepted that you should not wrap infants in excess clothing, cover their faces, or expose them to second hand smoke ─ either before or after birth.”

Prof Esterman says that despite lots of research going into the epidemiology of SIDS, many characteristics of the incidence of Sudden Infant Death Syndrome remain inexplicable.

“For example, male infants are 1.5 half times more likely to die from SIDS than females. The most at risk age is between one and three months. Researchers are now discovering some genetic factors, so it does run in families,” he said.

Dr Sarah Blunden, psychologist and research fellow at UniSA’s Centre for Sleep Research, explains a theory that SIDS could be linked with sleep breathing disorders.

“Sometimes during sleep, for some reason or another, children and adults will often stop breathing. The more severe the disorder, the more the airway shuts off. This can stop oxygen getting to the brain, or cause restless sleep,” she said.

Dr Blunden says that in adults, this is called sleep apnoea, and they will wake up as a defence mechanism.

“They will grumble and groan and go back to sleep. But in children that doesn’t happen as much. Children who have any sleep breathing disorder often don’t wake up at all ─ or at least not by the measurements that we currently use. We believe that children have a higher threshold for what we call arousal. They also have a higher threshold for the amount of oxygen that can be depleted before their body wakes them up. This is of course dangerous in terms of SIDS.

“Many of these infants have an event which in paediatric terms is called ALTE (apparent life threatening events) ─ where the child has stopped breathing but hasn’t died from it. Children who experience ALTE may have a higher threshold of arousal than other children, and this could quite possibly translate into have a higher propensity to suffer SIDS,” said Blunden.

Studies have also found that Indigenous and Torres Straight Islander infants are six times more likely of dying from SIDS than infants from non-Indigenous backgrounds.

Dr Blunden says that while environmental factors and problems associated with low socio-economic standards could play a part, the possibility of anthropological differences causing variation between Indigenous and non-Indigenous mortality rates in infants has not yet been ruled out.

“In Maori and Torres Straight Islander adults there is a greater percentage of sleep disordered breathing. This is attributed to morphology of the jaw and the neck in those populations,” said Dr Blunden.

“There could be a possibility that Indigenous infants have a similar morphology of the jaw, but I am unaware of any studies into this area.”

Prof Esterman says that decreasing the already low SIDS mortality rate will be a challenge.

“The trouble is that we’ve made such huge inroads ─ a 73 per cent reduction ─ in the last 10 years by successfully attacking modifiable risk factors like the sleeping position of the infant. What remains now are those risk factors which are much more difficult to modify, such as maternal smoking and genetic factors.”

Parents can largely reduce the risks of SIDS by following the simple care advice provided for babies. Dr Blunden also advises that infants should not to sleep with pillows, toys or cushion cot protectors.

Prof Esterman also points to recent research that has shown the use of dummies at sleep time has a protective effect (but only after the infant is well-established in breastfeeding), and recommends infants sleep in cots next to parent’s beds, rather than in the bed itself.

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