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doi:10.1111/jpc.12624
VIEWPOINT
Howard Williams oration: Preventing the unpreventable: The ‘cot death’ story Edwin A Mitchell Department of Paediatrics, The University of Auckland, Auckland, New Zealand
Key words:
epidemiology; prevention; risk factors; SIDS.
An internet search of ‘SIDS’ and ‘unpreventable’ produces over 8000 hits. Many websites state that sudden infant death syndrome (SIDS) ‘is an unpredictable, unpreventable, unexplained tragedy’. In this paper, I would like to challenge the statement that SIDS is unpreventable. This paper describes my 29-year journey and address the following: • Where we were in 1980s • The New Zealand Cot Death Study • The prevention programme (‘Back to Sleep’, ‘Reduce The Risk’) • The reduction in SIDS and post-neonatal mortality • What this tells us about the mechanism • Current challenges • Future prevention strategies
Where We Were in 1980s In New Zealand in the mid-1980s, there was a concern about the high rate for post-neonatal mortality (ages 1–11 months) which was much higher than other comparable countries.1 Furthermore, this rate had not changed in 20 years.2 The high rate appeared to be due to SIDS (see Appendix I for discussion of definitions) as the total rate for all other causes of death was similar (2.0–2.2/1000 live births). In New Zealand in 1984, there were 258 deaths that were attributed to SIDS (or cot death as it was more colloquially known). This was a rate of 5.0/1000 or one in 200 infants.3 Infant death records are matched with corresponding birth registration forms each year with the objective of validating ethnic status of deceased infants. This match enables information on birthweight, gestation and age of mother to be added to the death file. This showed the higher risk for male infants, Maori, those born with low birthweight or preterm and those born to young mothers. It showed the characteristic age distribution with few deaths in the first month of life, peaking at 2–3 months, and 90% of deaths occurring before 6 months of age. It showed a striking winter peak and a higher rate with increasing latitude.1 The Department of Health (now Ministry of Health) asked each health district to establish a confidential enquiry into Correspondence: Professor Edwin A Mitchell, Department of Paediatrics, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand. Fax: (+64 9) 373 7486; email: [email protected] Conflict of interest: The author has no conflict of interest. Accepted for publication 11 January 2014.
post-neonatal deaths, with the aim of identifying preventable deaths and develop and recommend prevention strategies thus reducing infant mortality at a local level. I chaired the Auckland post-neonatal mortality review committee. All cases were identified by Dr David Becroft, a paediatric pathologist, and checked against death certification. Parents of cases were interviewed by medical officers using a semi-structured questionnaire. We reported our first 2 years experience (1984– 1985).4 There were 134 post-neonatal deaths of which 80 (60%) were SIDS. Other causes were congenital anomalies, 24 (18%); infections, nine (7%); perinatal problems, eight (6%); and other, 13 (10%). Potential preventable deaths were infrequent (n = 14, 10%). These included the nine deaths from infection, two road traffic crashes, an accidental strangulation, a death secondary to birth trauma and an accidental displacement of tracheostomy tube. The risk factors identified at the national level were apparent within the Auckland cases. However, the importance of some ‘notable factors’ could not be interpreted as the prevalence of these factors in healthy infants was not known, for example, in 15% of deaths, the infant was bed sharing with another person; 11% had pallor, cyanotic or apnoeas episodes; and 20% had a change in environment or routine in 24 h before the death. This review confirmed the importance of SIDS as the major cause of post-neonatal mortality, identified that preventable deaths were infrequent and could not establish the importance of some putative risk factors for SIDS as the prevalence of these factors in babies that did not die was not known.
New Zealand Cot Death Study The New Zealand Cot Death Study was a 3-year case-control study funded by the Medical Research Council (now Health Research Council) and Hawkes Bay Medical Research Foundation. The aim was to identify risk factors for SIDS, with a particular emphasis on describing infant care practices. The cases were aged 28 days through to the first birthday. The study ran from 1 November 1987 through to 31 October 1990. Eighty per cent of all births occurred in the study regions. The method of selection of controls ensured that they were representative of all births and had an age distribution and time of ‘death’ (nominated sleep) as expected for cases. A total of 1800 controls were selected.5 The major finding was the markedly increased risk of SIDS if the infant was placed prone to sleep for the last sleep (Table 1).6 We were not the first to suggest that prone sleeping was a risk;
Journal of Paediatrics and Child Health 50 (2014) 855–860 © 2014 The Author Journal of Paediatrics and Child Health © 2014 Paediatrics and Child Health Division (Royal Australasian College of Physicians).
855
Howard Williams oration: Cot death
EA Mitchell
Table 1 The percentage of cases and controls and the univariate OR and 95% CI for position infant placed to sleep
Back Side Front
Case
Control
OR (95% CI)
4.7 30.9 64.4
15.7 51.4 32.9
1.0 2.0 (1.2, 3.5) 6.6 (3.9, 11.3)
CI, confidence interval; OR, odds ratio.
indeed, Beal reported the first review of sleep position and SIDS in a letter to The Lancet in 1986.7 Independently, the first two meta-analyses of sleep position were published in this journal in the same issue in December 1991.8,9 That something so simple as infant sleeping position could be causally related to SIDS was not readily accepted. For example, Carpenter reported in 1972 that 20% of cases were supine compared with 42% of controls,10 but he interpreted this as due to suffocation on soft pillows and recommended they be removed (RG Carpenter, pers. comm.). Beal in 1978 reported that 69 of 116 (59%) of the cases less than 12 months of age were found face down.11 She interpreted this as an abnormality of baby who had not responded to partial respiratory obstruction. Many of the earlier studies had methodological problems. Apart from our own study, similarly well-designed studies from Avon, England12 and Tasmania, Australia13 around the same time were reporting similar associations. The New Zealand study also confirmed the importance of maternal smoking, not breastfeeding and bed sharing.6 In 1989, I was on sabbatical in London and was introduced to the concept of population attributable risk. This calculates the proportion of deaths that might be prevented if a risk factor was avoided, assuming that the risk factor was causally related to the death. I applied it to the first year’s results and was staggered that 52% of SIDS cases might be prevented if babies were not placed prone to sleep. Further, if maternal smoking, bottle feeding and prone sleeping position were avoided, then SIDS might be reduced by 79%.5 The unique contribution of the New Zealand Cot Death Study is summarised in Table 2.
The National SIDS Prevention Programme I took these results from the first year of the study to the Department of Health, and they immediately saw the importance and agreed to develop a prevention programme. This decision was also supported by the weight of evidence about prone sleeping position, maternal smoking and not breastfeeding, and their association with SIDS. It took almost a year and numerous meetings to get buy-in from all stakeholders.14 Their Health Promotion Unit produced an attractive poster (Fig. 1) and stickers for every newborn cot in obstetric units. A newsletter went to every general practitioner,15 and education sessions were organised for Plunket nurses and midwives. This ensured that stakeholders were fully informed before the prevention programme went public. The Cot Death Association 856
Table 2
Unique contribution of the New Zealand cot death study
Identified risk factors that had not been considered previously Side sleeping position Interaction between smoking and bed sharing The protective effect of pacifiers (dummies) The protective effect of sleeping in the same bedroom as the parents Smoking by the father Post-natal depression First to apply the following concepts to SIDS Modifiable risk factor Population attributable risk Identified that the increased risk in Maori was explained by higher prevalence of maternal smoking and parental bed sharing with infant First to describe the epidemiology of SIDS after Back to Sleep campaign SIDS, sudden infant death syndrome.
funded commercials on television, and this was linked to Red Nose Day, which was then a major fundraiser for them. The prevention programme was launched in February 1991 to much fanfare, but infant sleep position was changing before then as health-care workers started advising parents not to place baby prone to sleep.16 The publicity crossed the Tasman Sea, and Australia followed our lead in May 1991. In the UK, an ITV documentary (‘Every mother’s nightmare’) on the cot death of Sebastian Diamond, the son of Anne Diamond, a very popular newscaster, focused on the New Zealand research and prevention initiative. The UK launched their programme which was brilliantly entitled ‘Back to Sleep’ in November 1991. Other countries followed our lead, although in the USA, it took until 1994 before their campaign was launched. The prevention messages evolved from the original three messages focusing on prone sleeping position, maternal smoking and not breastfeeding. In 1992, advice to parents not to bed share with their infants was added to these messages. This turned out to be controversial as discussed below. The sleep position message originally recommended ‘side or back’, but as further evidence of the risk from side position became apparent, this was changed to ‘back or side’ and then to ‘back’ only.
The Reduction in Mortality The SIDS mortality rate fell immediately. That this was real and not due to diagnostic transfer was shown by the corresponding fall in total post-neonatal mortality, which as stated earlier had not changed for 20 years (1982–1989: mean rate 6.4/1000). In 1990, it fell to 4.2/1000 and by 1992 to 3.6/1000. A survey in South Auckland showed that this initial fall was due to the reduction in prone sleeping position, with no significant change in maternal smoking or breastfeeding rates.17 The surveys showed that most infants were placed on their side to
Journal of Paediatrics and Child Health 50 (2014) 855–860 © 2014 The Author Journal of Paediatrics and Child Health © 2014 Paediatrics and Child Health Division (Royal Australasian College of Physicians)
EA Mitchell
Howard Williams oration: Cot death
Fig. 1 The Help Prevent Cot Death poster was designed for display by health-care providers to raise awareness about the Help Prevent Cot Death programme and carried health messages and a menu of information sources. The message ‘side or back’ subsequently changed to ‘back or side’ then to ‘back’ as more evidence accumulated as to the risk of sudden infant death syndrome (SIDS) from side sleeping position.
sleep. Mortality continued to decrease over the next few years, and by 2001, it was down to 2.1/1000. This has been attributed to the avoidance of the side sleeping position.18 This simple prevention message has saved countless lives around the world. We have estimated that it has saved 3000 lives in New Zealand, 17 000 lives in England and Wales, and 40 000 lives in the USA.19
What This Tells Us about the Mechanism There were two features about the reduction in mortality which were entirely unexpected. We observed that the high death rate in the winter months was attenuated and that the higher rate in the South Island disappeared.20 We subsequently showed that the magnitude of the risk of SIDS from prone sleeping position was highest in winter (adjusted odds ratio (adjOR) = 9.4), lowest in summer (adjOR = 2.1) and intermediate for autumn and spring (adjOR = 2.9 and 2.5, respectively).21 Similarly, the risk from prone sleeping was higher in the South Island than the North Island.22 Case-control studies from Avon, England12 and Tasmania, Australia23 showed that prone sleeping position was a bigger risk in the presence of minor illness and excessive thermal insulation from clothing and in particular bedding than in the absence of these conditions. We confirmed these findings.24,25 Further, we found that prone sleeping position was more risky at day than during the night.26 This was confirmed in the German SIDS case-control study.27 In Austria, there is an increased risk of SIDS with higher altitude, and this is primarily in combination with prone sleeping position.28 SIDS mortality is higher in the states with higher altitudes than states with lower altitudes, and this mortality differential decreased with implementation of the ‘Back to Sleep’ campaign.29 The risk of SIDS with prone sleeping position is modified by season, illness, thermal insulation, time of day, latitude and
altitude. This suggests that the mechanism by which prone sleeping position causes SIDS is in some way related to temperature, but it does not tell us the actual mechanism.
Current Challenges Although mortality has dropped dramatically, it continues to be the major cause of death in the post-neonatal age group. In New Zealand, there are about 60 sudden unexpected death in infancy (SUDI) deaths per annum. The bed sharing issue has been controversial, with some groups encouraging bed sharing to promote breastfeeding. Anthropologists in particular argued that bed sharing may be protective against SIDS.30 Further, some have argued about the cultural importance of bed sharing,31 and thus, the recommendation not to bed share with their infant has been interpreted as an attack on their culture. This controversy meant that many health professionals avoided giving any advice to parents or gave mixed messages. It is hardly surprising that less than 50% of women with young infants know that bed sharing increased the risk of SIDS.32 With the reduction in deaths attributed to the prone sleeping position, bed sharing has proportionately become more important. This is illustrated by the observation in New Zealand and other countries that 50–70% of SUDIs are now occurring in a bed sharing situation,33 and this reaches 90%+ in the first month of life.34 In a 10-year review in Auckland, 64% of infant deaths referred to the coroner were bed sharing, and this was 92% in those less than 1 month of age.35 Of course, the association of death with bed sharing is not new; indeed, the first reference is in the Old Testament. These deaths were often attributed to overlaying. However, we were the first to associate it to SIDS, where frank overlaying was not present.6 There are now 11 studies that confirm bed sharing is a risk for SIDS/SUDI (pooled OR = 2.9).36 We were the first to show that there was an interaction with maternal smoking,
Journal of Paediatrics and Child Health 50 (2014) 855–860 © 2014 The Author Journal of Paediatrics and Child Health © 2014 Paediatrics and Child Health Division (Royal Australasian College of Physicians)
857
Howard Williams oration: Cot death
EA Mitchell
such that the risk of was much higher in infants of mothers who smoked than for infants of non-smokers,37 and this has been confirmed by others. Carpenter et al. made the next advance showing an interaction with age, such that the risk was highest in infants less than 1 month of age and that this risk decreased as the infant got older.38 Blair et al. confirmed the observation that parents who drank alcohol and bed shared with baby increased the risk of SUDI.39 This lead to the concept that it is not bed sharing that is the risk per se but the circumstances surrounding it.33 This concept was always unlikely as infants placed back into their own cot after breastfeeding or cuddles and infants in the same bed as an awake mother were not at risk of death. However, the recent publication by Carpenter et al. has clarified the risks. In the lowest risk group (mother aged 26–30, second child, normal birthweight) and following current advice (non-smoking parents, breastfeeding, room sharing but not bed sharing), the risk of SIDS is very low (0.08/1000), which equates to just five to six deaths per annum in New Zealand.40 However, if this very low-risk baby bed shares, then the risk is increased almost threefold to 0.23/1000. Maternal smoking increases the baseline risk, but if this smoking mother also bed shares, the risk is increased almost 10 fold to 1.27/1000, additionally if alcohol is drunk the risk increases 16-fold to 27.5/1000. If you add other factors, then the risk becomes even higher. To summarise, the risk from bed sharing is increased in the following groups: • Infants of mothers who smoke or smoked in pregnancy • Maternal alcohol, drugs, excessive tiredness • Maternal obesity • Vulnerable babies (e.g. preterm, low birthweight) • Young infants, especially less than 3 months • There is a small increased risk when the mother does not smoke in infants
doi:10.1111/jpc.12624
VIEWPOINT
Howard Williams oration: Preventing the unpreventable: The ‘cot death’ story Edwin A Mitchell Department of Paediatrics, The University of Auckland, Auckland, New Zealand
Key words:
epidemiology; prevention; risk factors; SIDS.
An internet search of ‘SIDS’ and ‘unpreventable’ produces over 8000 hits. Many websites state that sudden infant death syndrome (SIDS) ‘is an unpredictable, unpreventable, unexplained tragedy’. In this paper, I would like to challenge the statement that SIDS is unpreventable. This paper describes my 29-year journey and address the following: • Where we were in 1980s • The New Zealand Cot Death Study • The prevention programme (‘Back to Sleep’, ‘Reduce The Risk’) • The reduction in SIDS and post-neonatal mortality • What this tells us about the mechanism • Current challenges • Future prevention strategies
Where We Were in 1980s In New Zealand in the mid-1980s, there was a concern about the high rate for post-neonatal mortality (ages 1–11 months) which was much higher than other comparable countries.1 Furthermore, this rate had not changed in 20 years.2 The high rate appeared to be due to SIDS (see Appendix I for discussion of definitions) as the total rate for all other causes of death was similar (2.0–2.2/1000 live births). In New Zealand in 1984, there were 258 deaths that were attributed to SIDS (or cot death as it was more colloquially known). This was a rate of 5.0/1000 or one in 200 infants.3 Infant death records are matched with corresponding birth registration forms each year with the objective of validating ethnic status of deceased infants. This match enables information on birthweight, gestation and age of mother to be added to the death file. This showed the higher risk for male infants, Maori, those born with low birthweight or preterm and those born to young mothers. It showed the characteristic age distribution with few deaths in the first month of life, peaking at 2–3 months, and 90% of deaths occurring before 6 months of age. It showed a striking winter peak and a higher rate with increasing latitude.1 The Department of Health (now Ministry of Health) asked each health district to establish a confidential enquiry into Correspondence: Professor Edwin A Mitchell, Department of Paediatrics, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand. Fax: (+64 9) 373 7486; email: [email protected] Conflict of interest: The author has no conflict of interest. Accepted for publication 11 January 2014.
post-neonatal deaths, with the aim of identifying preventable deaths and develop and recommend prevention strategies thus reducing infant mortality at a local level. I chaired the Auckland post-neonatal mortality review committee. All cases were identified by Dr David Becroft, a paediatric pathologist, and checked against death certification. Parents of cases were interviewed by medical officers using a semi-structured questionnaire. We reported our first 2 years experience (1984– 1985).4 There were 134 post-neonatal deaths of which 80 (60%) were SIDS. Other causes were congenital anomalies, 24 (18%); infections, nine (7%); perinatal problems, eight (6%); and other, 13 (10%). Potential preventable deaths were infrequent (n = 14, 10%). These included the nine deaths from infection, two road traffic crashes, an accidental strangulation, a death secondary to birth trauma and an accidental displacement of tracheostomy tube. The risk factors identified at the national level were apparent within the Auckland cases. However, the importance of some ‘notable factors’ could not be interpreted as the prevalence of these factors in healthy infants was not known, for example, in 15% of deaths, the infant was bed sharing with another person; 11% had pallor, cyanotic or apnoeas episodes; and 20% had a change in environment or routine in 24 h before the death. This review confirmed the importance of SIDS as the major cause of post-neonatal mortality, identified that preventable deaths were infrequent and could not establish the importance of some putative risk factors for SIDS as the prevalence of these factors in babies that did not die was not known.
New Zealand Cot Death Study The New Zealand Cot Death Study was a 3-year case-control study funded by the Medical Research Council (now Health Research Council) and Hawkes Bay Medical Research Foundation. The aim was to identify risk factors for SIDS, with a particular emphasis on describing infant care practices. The cases were aged 28 days through to the first birthday. The study ran from 1 November 1987 through to 31 October 1990. Eighty per cent of all births occurred in the study regions. The method of selection of controls ensured that they were representative of all births and had an age distribution and time of ‘death’ (nominated sleep) as expected for cases. A total of 1800 controls were selected.5 The major finding was the markedly increased risk of SIDS if the infant was placed prone to sleep for the last sleep (Table 1).6 We were not the first to suggest that prone sleeping was a risk;
Journal of Paediatrics and Child Health 50 (2014) 855–860 © 2014 The Author Journal of Paediatrics and Child Health © 2014 Paediatrics and Child Health Division (Royal Australasian College of Physicians).
855
Howard Williams oration: Cot death
EA Mitchell
Table 1 The percentage of cases and controls and the univariate OR and 95% CI for position infant placed to sleep
Back Side Front
Case
Control
OR (95% CI)
4.7 30.9 64.4
15.7 51.4 32.9
1.0 2.0 (1.2, 3.5) 6.6 (3.9, 11.3)
CI, confidence interval; OR, odds ratio.
indeed, Beal reported the first review of sleep position and SIDS in a letter to The Lancet in 1986.7 Independently, the first two meta-analyses of sleep position were published in this journal in the same issue in December 1991.8,9 That something so simple as infant sleeping position could be causally related to SIDS was not readily accepted. For example, Carpenter reported in 1972 that 20% of cases were supine compared with 42% of controls,10 but he interpreted this as due to suffocation on soft pillows and recommended they be removed (RG Carpenter, pers. comm.). Beal in 1978 reported that 69 of 116 (59%) of the cases less than 12 months of age were found face down.11 She interpreted this as an abnormality of baby who had not responded to partial respiratory obstruction. Many of the earlier studies had methodological problems. Apart from our own study, similarly well-designed studies from Avon, England12 and Tasmania, Australia13 around the same time were reporting similar associations. The New Zealand study also confirmed the importance of maternal smoking, not breastfeeding and bed sharing.6 In 1989, I was on sabbatical in London and was introduced to the concept of population attributable risk. This calculates the proportion of deaths that might be prevented if a risk factor was avoided, assuming that the risk factor was causally related to the death. I applied it to the first year’s results and was staggered that 52% of SIDS cases might be prevented if babies were not placed prone to sleep. Further, if maternal smoking, bottle feeding and prone sleeping position were avoided, then SIDS might be reduced by 79%.5 The unique contribution of the New Zealand Cot Death Study is summarised in Table 2.
The National SIDS Prevention Programme I took these results from the first year of the study to the Department of Health, and they immediately saw the importance and agreed to develop a prevention programme. This decision was also supported by the weight of evidence about prone sleeping position, maternal smoking and not breastfeeding, and their association with SIDS. It took almost a year and numerous meetings to get buy-in from all stakeholders.14 Their Health Promotion Unit produced an attractive poster (Fig. 1) and stickers for every newborn cot in obstetric units. A newsletter went to every general practitioner,15 and education sessions were organised for Plunket nurses and midwives. This ensured that stakeholders were fully informed before the prevention programme went public. The Cot Death Association 856
Table 2
Unique contribution of the New Zealand cot death study
Identified risk factors that had not been considered previously Side sleeping position Interaction between smoking and bed sharing The protective effect of pacifiers (dummies) The protective effect of sleeping in the same bedroom as the parents Smoking by the father Post-natal depression First to apply the following concepts to SIDS Modifiable risk factor Population attributable risk Identified that the increased risk in Maori was explained by higher prevalence of maternal smoking and parental bed sharing with infant First to describe the epidemiology of SIDS after Back to Sleep campaign SIDS, sudden infant death syndrome.
funded commercials on television, and this was linked to Red Nose Day, which was then a major fundraiser for them. The prevention programme was launched in February 1991 to much fanfare, but infant sleep position was changing before then as health-care workers started advising parents not to place baby prone to sleep.16 The publicity crossed the Tasman Sea, and Australia followed our lead in May 1991. In the UK, an ITV documentary (‘Every mother’s nightmare’) on the cot death of Sebastian Diamond, the son of Anne Diamond, a very popular newscaster, focused on the New Zealand research and prevention initiative. The UK launched their programme which was brilliantly entitled ‘Back to Sleep’ in November 1991. Other countries followed our lead, although in the USA, it took until 1994 before their campaign was launched. The prevention messages evolved from the original three messages focusing on prone sleeping position, maternal smoking and not breastfeeding. In 1992, advice to parents not to bed share with their infants was added to these messages. This turned out to be controversial as discussed below. The sleep position message originally recommended ‘side or back’, but as further evidence of the risk from side position became apparent, this was changed to ‘back or side’ and then to ‘back’ only.
The Reduction in Mortality The SIDS mortality rate fell immediately. That this was real and not due to diagnostic transfer was shown by the corresponding fall in total post-neonatal mortality, which as stated earlier had not changed for 20 years (1982–1989: mean rate 6.4/1000). In 1990, it fell to 4.2/1000 and by 1992 to 3.6/1000. A survey in South Auckland showed that this initial fall was due to the reduction in prone sleeping position, with no significant change in maternal smoking or breastfeeding rates.17 The surveys showed that most infants were placed on their side to
Journal of Paediatrics and Child Health 50 (2014) 855–860 © 2014 The Author Journal of Paediatrics and Child Health © 2014 Paediatrics and Child Health Division (Royal Australasian College of Physicians)
EA Mitchell
Howard Williams oration: Cot death
Fig. 1 The Help Prevent Cot Death poster was designed for display by health-care providers to raise awareness about the Help Prevent Cot Death programme and carried health messages and a menu of information sources. The message ‘side or back’ subsequently changed to ‘back or side’ then to ‘back’ as more evidence accumulated as to the risk of sudden infant death syndrome (SIDS) from side sleeping position.
sleep. Mortality continued to decrease over the next few years, and by 2001, it was down to 2.1/1000. This has been attributed to the avoidance of the side sleeping position.18 This simple prevention message has saved countless lives around the world. We have estimated that it has saved 3000 lives in New Zealand, 17 000 lives in England and Wales, and 40 000 lives in the USA.19
What This Tells Us about the Mechanism There were two features about the reduction in mortality which were entirely unexpected. We observed that the high death rate in the winter months was attenuated and that the higher rate in the South Island disappeared.20 We subsequently showed that the magnitude of the risk of SIDS from prone sleeping position was highest in winter (adjusted odds ratio (adjOR) = 9.4), lowest in summer (adjOR = 2.1) and intermediate for autumn and spring (adjOR = 2.9 and 2.5, respectively).21 Similarly, the risk from prone sleeping was higher in the South Island than the North Island.22 Case-control studies from Avon, England12 and Tasmania, Australia23 showed that prone sleeping position was a bigger risk in the presence of minor illness and excessive thermal insulation from clothing and in particular bedding than in the absence of these conditions. We confirmed these findings.24,25 Further, we found that prone sleeping position was more risky at day than during the night.26 This was confirmed in the German SIDS case-control study.27 In Austria, there is an increased risk of SIDS with higher altitude, and this is primarily in combination with prone sleeping position.28 SIDS mortality is higher in the states with higher altitudes than states with lower altitudes, and this mortality differential decreased with implementation of the ‘Back to Sleep’ campaign.29 The risk of SIDS with prone sleeping position is modified by season, illness, thermal insulation, time of day, latitude and
altitude. This suggests that the mechanism by which prone sleeping position causes SIDS is in some way related to temperature, but it does not tell us the actual mechanism.
Current Challenges Although mortality has dropped dramatically, it continues to be the major cause of death in the post-neonatal age group. In New Zealand, there are about 60 sudden unexpected death in infancy (SUDI) deaths per annum. The bed sharing issue has been controversial, with some groups encouraging bed sharing to promote breastfeeding. Anthropologists in particular argued that bed sharing may be protective against SIDS.30 Further, some have argued about the cultural importance of bed sharing,31 and thus, the recommendation not to bed share with their infant has been interpreted as an attack on their culture. This controversy meant that many health professionals avoided giving any advice to parents or gave mixed messages. It is hardly surprising that less than 50% of women with young infants know that bed sharing increased the risk of SIDS.32 With the reduction in deaths attributed to the prone sleeping position, bed sharing has proportionately become more important. This is illustrated by the observation in New Zealand and other countries that 50–70% of SUDIs are now occurring in a bed sharing situation,33 and this reaches 90%+ in the first month of life.34 In a 10-year review in Auckland, 64% of infant deaths referred to the coroner were bed sharing, and this was 92% in those less than 1 month of age.35 Of course, the association of death with bed sharing is not new; indeed, the first reference is in the Old Testament. These deaths were often attributed to overlaying. However, we were the first to associate it to SIDS, where frank overlaying was not present.6 There are now 11 studies that confirm bed sharing is a risk for SIDS/SUDI (pooled OR = 2.9).36 We were the first to show that there was an interaction with maternal smoking,
Journal of Paediatrics and Child Health 50 (2014) 855–860 © 2014 The Author Journal of Paediatrics and Child Health © 2014 Paediatrics and Child Health Division (Royal Australasian College of Physicians)
857
Howard Williams oration: Cot death
EA Mitchell
such that the risk of was much higher in infants of mothers who smoked than for infants of non-smokers,37 and this has been confirmed by others. Carpenter et al. made the next advance showing an interaction with age, such that the risk was highest in infants less than 1 month of age and that this risk decreased as the infant got older.38 Blair et al. confirmed the observation that parents who drank alcohol and bed shared with baby increased the risk of SUDI.39 This lead to the concept that it is not bed sharing that is the risk per se but the circumstances surrounding it.33 This concept was always unlikely as infants placed back into their own cot after breastfeeding or cuddles and infants in the same bed as an awake mother were not at risk of death. However, the recent publication by Carpenter et al. has clarified the risks. In the lowest risk group (mother aged 26–30, second child, normal birthweight) and following current advice (non-smoking parents, breastfeeding, room sharing but not bed sharing), the risk of SIDS is very low (0.08/1000), which equates to just five to six deaths per annum in New Zealand.40 However, if this very low-risk baby bed shares, then the risk is increased almost threefold to 0.23/1000. Maternal smoking increases the baseline risk, but if this smoking mother also bed shares, the risk is increased almost 10 fold to 1.27/1000, additionally if alcohol is drunk the risk increases 16-fold to 27.5/1000. If you add other factors, then the risk becomes even higher. To summarise, the risk from bed sharing is increased in the following groups: • Infants of mothers who smoke or smoked in pregnancy • Maternal alcohol, drugs, excessive tiredness • Maternal obesity • Vulnerable babies (e.g. preterm, low birthweight) • Young infants, especially less than 3 months • There is a small increased risk when the mother does not smoke in infants
