Several international studies have found that the promotion of "back-to-sleep" campaigns based on the findings of many epidemiological studies has led to a dramatic decrease in the global prevalence of SIDS over the last 2 decades (10
). However, few studies have examined the prevalence of SIDS specifically within Korea (12
), and no coronial data regarding SIDS in Korea have been reported. To redress this lack of research within a Korean context, we examined the factors associated with SIDS cases that had been reported to the National Forensic Services and Seoul National University College of Medicine, the majority of which had occurred in the Seoul-Gyeonggi region of Korea, between 1996 and 2008.
Analysis of the data indicates that the majority of the deaths due to SIDS had occurred while the infants had been sleeping in a hazardous sleep environment. While many were found in a prone sleeping position, which has been reported as one of the established risk factors for SIDS (10
), a recent study reported that risk of SIDS in a side position is of a similar magnitude to that of a prone position (14
). The risk posed by sleeping in a side position might be due to its inherent instability, as it allows the infant to easily move into a prone position. Therefore, the American Academy of Pediatrics (AAP) strongly recommends that infants always be placed in a supine sleeping position (15
). Among the cases in this study, 55.4% (93 cases) had been placed to sleep in a prone position, a rate much higher than rates previously reported, which range from 13% to 43% (16
), and 17.3% (29 cases) in a side position. Analysis of the data indicated no tendency toward a change in sleeping position to the recommended position (supine) over the 13-yr study period.
Interestingly, 34% (108 cases) of the SIDS analyzed in this study occurred outside the home, including in a nursery/daycare setting or a relative's accommodation, indicating increased risk of SIDS outside the parental residence. This might be due to infants who sleep outside the home being placed in a sleep environment not specifically arranged for infants and/or being placed in a prone position. The study data support this hypothesis, as analysis of the difference between the prevalence in which the infants in this study had been placed in a prone sleeping position in a setting outside the home compared to that in which they had been placed in a prone position in the home was found to be statistically significant (P = 0.002).
Among the cases for which bed-sharing had been reported, the prevalence of bed-sharing was 59.3% (121 cases), a much higher rate than those found in cohort-based studies, which range from 16.0% to 50.4% (21
). This finding might be explained by cultural factors, such as a Korean belief that bedsharing enables breastfeeding and emotional bonding, and supported by the finding that 22.5% (34 cases) of the mothers in this study reported breast-feeding as the reason for bed-sharing. However, bed-sharing is a known risk factor for SIDS, especially for infants under 3 months of age, infants who share a bed with an individual under the influence of alcohol, and infants who are subjected to bed-sharing for long durations (4
). Analysis of the data revealed that 44.6% (54 cases) for which bed-sharing had been reported had been under 3 months of age, a percentage that is statistically significant when compared to that of the non-bed-sharing cases and comprising approximately 69.2% of all cases for which bed-sharing had been reported under 3 months of age. Surprisingly, 17.4% (21 cases) occurred while bed-sharing with adult(s) who were under the influence of alcohol, a factor that may have undermined the ability to respond to the infant. Indeed, several studies have reported a strong association between alcohol consumption prior to bed-sharing and SIDS (4
). Furthermore, there was a significantly increasing trend in bed-sharing over 13-yr study period, suggesting that parents and caregivers should be provided with information regarding bed-sharing as a means to decrease the risk of SIDS. This suggestion is supported by the AAP, which recommends that infants in the first year should sleep in their own bed, ideally a bassinet or crib placed in the parental room (15
), as well as the findings of this study, specifically that only 16 (9.4%) infants had been sleeping in their own bed.
Regarding other risk and protective factors, a recent meta-analysis study reported that exclusive breast-feeding of any duration is protective against SIDS (26
). The prevalence of exclusive breast-feeding in this study was found to be 14.2%, a rate slightly higher than the 10.2% domestic rate reported in 2002 (27
). Unfortunately, accurate data regarding maternal smoking, which has been identified as a dependent risk factor contributing to SIDS (28
) and the main risk factor for SIDS during bed-sharing (11
), could not be collected.
The exact pathogenesis of SIDS remains poorly understood. Accumulating evidence has linked SIDS to a convergence of exogenous stressors, including non-recommended (prone or side) sleeping position, a critical development period in homeostatic condition, and dysfunction of cardiopulmonary and/or arousal system (29
). A recent study found a significant association between SIDS and mutations in the cardiac ion-channel protein giving rise to disease, including Long QT Syndrome (LQTS) and Brugada Syndrome, in 10 to 15% of SIDS cases (30
). Although there is no evidence of strong heritability for SIDS, the genetic alteration that has been observed could lead to vulnerability to SIDS (3
). Thus, continued research into the interaction between genetic and environmental factors is critical for SIDS prevention.
A 2004 study using the capture-recapture method to examine the 1998 and 1999 data estimated the rate of SIDS in Korea to be 0.56 per 1,000 live births (12
). However, this estimation is questionable due to lack of scientific validity in diagnosis, with many cases having been diagnosed as SIDS without postmortem examination and death scene investigation. Although autopsies are critical in identifying the cause of death whenever an infant dies suddenly from unknown causes, the autopsy rate in Korea, which is unknown, is presumed to be extremely low compared to those of other developed countries (3
Due to its retrospective design, this study faced a major limitation in data collection. Although a postmortem protocol for SIDS autopsy had been introduced in 2001, it was not widely used until 2006. Therefore, many data regarding parental smoking, sleeping surface, and breathing at time of death (i.e., whether the face had been covered) were unavailable for cases that occurred before 2006. In contrast, significantly more and better data were available after 2006 because of increased awareness of the environmental risk factors associated with SIDS and increased use of the postmortem protocol.
The findings of this study have crucial implications for health policymaking and practices. Specifically, they indicate the need to develop, adopt, and implement 1) a set of standardized guidelines for SIDS diagnosis; 2) a protocol for the collection of detailed data from medical doctors, scene investigators, caregivers, and medical examiners to determine the precise cause of death; and 3) monitoring systems to collect data with which to identify trends in SIDS prevalence. Moreover, they suggest that educational campaigns for SIDS prevention, which have traditionally-and effectively-emphasized avoidance of bed-sharing and placement in a prone position-should also stress avoidance of all risk factors and be conducted on a nationwide scale using all means of information distribution, including those provided by governmental, media, and medical sources.
In conclusion, this first coronial study of SIDS in Korea found that a considerable proportion of deaths due to SIDS occurred while the infants had been sleeping in an environment characterized by risk factors for SIDS, particularly placement in a prone or side position and/or in a bed-sharing situation. This finding strongly suggests that immediate focus should be placed on making the sleeping environment safer for the next generation.