Sudden unexpected infant deaths (SUID) accounted for 1 in 3 postneonatal deaths in 2010. Sudden infant death syndrome and accidental sleep-related suffocation are among the most frequently reported types of SUID. The causes of these SUID usually are not obvious before a medico-legal investigation and may remain unexplained even after investigation. Lack of consistent investigation practices and an autopsy marker make it difficult to distinguish sudden infant death syndrome from other SUID. Standardized categories might assist in differentiating SUID subtypes and allow for more accurate monitoring of the magnitude of SUID, as well as an enhanced ability to characterize the highest risk groups. To capture information about the extent to which cases are thoroughly investigated and how factors like unsafe sleep may contribute to deaths, CDC created a multistate SUID Case Registry in 2009. As part of the registry, the Centers for Disease Control and Prevention developed a classification system that recognizes the uncertainty about how suffocation or asphyxiation may contribute to death and that accounts for unknown and incomplete information about the death scene and autopsy. This report describes the classification system, including its definitions and decision-making algorithm, and applies the system to 436 US SUID cases that occurred in 2011 and were reported to the registry. These categories, although not replacing official cause-of-death determinations, allow local and state programs to track SUID subtypes, creating a valuable tool to identify gaps in investigation and inform SUID reduction strategies.
Classification System for the Sudden Unexpected Infant Death Case Registry and its Application
FINANCIAL DISCLOSURE: Ms Covington’s agency, the Michigan Public Health Institute, received funds from EGS that originated at the Centers for Disease Control and Prevention in the amount of $233,076.48 for the period April 1, 2009 to May 31, 2011, to develop and support components of the SUID Case Registry described in the article (reference 09FED907750, contract GS07F67053R). The other authors have indicated they have no financial relationships relevant to this article to disclose.
Carrie K. Shapiro-Mendoza, Lena Camperlengo, Rebecca Ludvigsen, Carri Cottengim, Robert N. Anderson, Thomas Andrew, Theresa Covington, Fern R. Hauck, James Kemp, Marian MacDorman; Classification System for the Sudden Unexpected Infant Death Case Registry and its Application. Pediatrics July 2014; 134 (1): e210–e219. 10.1542/peds.2014-0180
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In reply:
We appreciate the thoughtful comments by Dr. Bien. The incidence of scooter-related injuries continue to rise. In March 2001, the U.S. Consumer Product Safety Commission reported 8,130. These statistics approximate those from last September when record numbers of injuries were reported. Since the summer of 2000 four children have died while riding scooters.(1) The need for consumer education is imperative inorder to reduce the injuries associated with scooter riding, especially in young children. Anticipatory guidance by pediatricians as well as responsible marketing by manufacturers and retailers will hopefully continue to impact on the public.
Dr. Bien's comment on wrist guards and scooter riding deserves mention. Traditional wrist guards used for inline skating are not appropriate for scooter riding. Wrist guards may limit the rider's ability to grip the handlebars and steer the scooter. Until styles are manufactured specifically for scooter riding, the use of wrist guards is not recommended. The benefits of knee and elbow protection, as well as helmet use, is significant and should be advocated.
(1) Consumer Product Safety Commission. Scooter Information. Available at: http://www.cpsc.gov/pr/prscoot.html. Accessioned May 31,2001.
In Reply
We appreciate the opportunity to respond to the points raised in Dr. Willinger's letter.(1)
As noted in our article, the classification system(2) was designed to address state and local public health surveillance needs and to complement vital records surveillance. Although the system does not specifically address clinical research needs, we encourage researchers to adapt the system to further explore pathophysiologic pathways of sudden infant death syndrome (SIDS) and sudden unexpected infant deaths (SUID).
We fully acknowledged that our classification system does not have a category explicitly labeled SIDS and that categories do not distinguish SIDS and SUID cases. Although Dr. Willinger argues that SIDS has distinct biological properties that differ from other SUID and that it should be its own entity, understanding of its biologic characteristics continues to evolve. Thus, our classification system does not use categories that distinguish potential pathophysiologic pathways for SIDS or differentiate SIDS from SUID. Instead, categories can be grouped to serve specific research needs. For example, to explore pathophysiologic pathways or infant vulnerabilities, such as brainstem abnormalities and cardiac channelopathies, researchers could use categories to exclude cases without a complete investigation and cases with strong evidence for suffocation.
Although our classification system does not distinguish cases that occur during sleep from those that occur while awake, deaths where an infant is awake and then is witnessed unresponsive fall into the category "No unsafe sleep factors." Among the nearly 1000 cases reviewed, less than 5 involved infants who were awake and then witnessed unresponsive. The flexibility of our system would allow for creating a new category if in the future more such cases are documented. Notably, the 1989 NICHD expert panel did not include sleep status in their definition of SIDS.(3)
Regarding quantification of degree of suffocation risk, our system distinguishes between those cases that occurred in potentially unsafe environments but where suffocation was unlikely and those cases in which unsafe sleep factors likely contributed to suffocation. We showed that among cases with complete investigations, more than 50% occurred without evidence of suffocation. Nevertheless, fewer than1% of cases occurred in a recommended sleep environment--i.e., where the infant was on their back, in a crib, and without any potentially asphyxiating objects. Thus, our data do not support the perception that most SUID can be attributed to accidental suffocation.
Finally, Dr. Willinger asserts that medical examiners are using risk factors, such as prone sleep and bedsharing, as causes of death instead of SIDS. Although deaths attributed to accidental sleep-related suffocation have increased since the 1990s, deaths due to unknown/undetermined causes have also increased.(4) Concurrently, SIDS has remained the most frequently reported SUID among these causes. In 2011, the most recent year for which data were available, of the three most frequently reported SUID causes, most deaths were classified as SIDS (56%), followed by unknown/undetermined cause (26%) and accidental suffocation and strangulation in bed (18%).(5) As with SIDS, considerations for the practice of designating unresolved cases as undetermined or unknown cause also remain consistent with 1989 expert deliberations.(3)
Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.
1. Willinger M. Limitations of the SUID Case Registry classification Ssystem [E-letter]. Pediatrics (September 16, 2014); http://pediatrics.aappublications.org/content/134/1/e210/reply#pediatrics_el_63939 (accessed September 29, 2014).
2. Shapiro-Mendoza CK, Camperlengo LT, Ludvigsen R, Cottengim C, Anderson RN, Andrew T, Covington T, Hauck FR, Kemp J, MacDorman Ml. Classification system for the Sudden Unexpected Infant Death Case Registry and its application. Pediatrics 2014 134:e210-e219; doi:10.1542/peds.2014- 0180.
3. Willinger M, James LS, Catz C. Defining the sudden infant death syndrome (SIDS): deliberations of an expert panel convened by the National Institute of Child Health and Human Development. Pediatr Path. 1991;11:677 -684.
4. Shapiro-Mendoza CK, Kimball M, Tomashek KM, Anderson RN, Blanding S. US infant mortality trends attributable to accidental suffocation and strangulation in bed from 1984 through 2004: are rates increasing? Pediatrics. 2009 Feb;123(2):533-9.
5. Centers for Disease Control and Prevention, National Center for Health Statistics. Compressed Mortality File 1999-2011 on CDC WONDER Online Database, released July 2014. Data are compiled from Compressed Mortality File 1999-2011 Series 20 No. 2Q, 2014. Accessed at http://wonder.cdc.gov/cmf-icd10.html on Sep 29, 2014 9:52:09 AM.
Conflict of Interest:
Authors have no competing interests.
Limitations of the SUID Case Registry Classification System
Shapiro-Mendoza and co-authors propose a classification system for sudden unexpected infant deaths (SUID) for use by the SUID Case Registry to facilitate surveillance of the completeness of case investigation and "safety" of the infant sleep environment. By addressing specific surveillance needs only, the classification system proposed raises several concerns.
A major concern is that Sudden Infant Death Syndrome (SIDS) is not identified as an entity with distinct biological properties from other SUID. By creating categories that combine SIDS with other SUID, the classification system hinders our ability to pursue specific mechanisms of death for this syndrome. For example, many cases of SIDS have neurochemical abnormalities in brainstem regions involved in autonomic nervous system control not found in other SUID (1). There is also evidence suggesting that these autonomic system abnormalities originate in utero (2). In about 10-15% of cases diagnosed as SIDS, potentially lethal genetic cardiac channelopathies have been detected (3). It is hypothesized that these abnormalities create vulnerability in infancy to life- threatening respiratory, cardiovascular or thermal challenges during a sleep period. Also, an important characteristic of SIDS is that the deaths were unobserved by caregivers, but discovered after the infants had spent a period of sleep. However, the proposed system appears to combine deaths observed during wakeful states, as well as associated with sleep.
The proposed system does not account for the fact that the pathophysiologic pathway(s) of SIDS remains unknown. The categories distinguish between sudden unexplained deaths in "safe" sleep environments from those in "unsafe" sleep environments. By creating a classification system with categories that try to quantify the degree of potential suffocation risk, there is an implication that the potential for asphyxia in the environment is the pathophysiologic pathway in SIDS. Prone sleep position and bed sharing increase the risk for SIDS, but the physiologic mechanisms by which these practices increase risk is unknown. These include, but may not be limited to, an asphyxial challenge, a thermal challenge, or a cardiovascular stress.
The proposed classification system also assumes that the degree of suffocation risk can be used to phenotype the deaths. However, there is no evidence that the pathophysiology of sudden infant deaths that remain unexplained after a complete case investigation differ by the characteristics of the sleep environment. On the contrary, there is evidence that brainstem abnormalities are similar in sudden unexplained infant deaths regardless of the presence or absence of potential asphyxia risk in the sleep environment (4).
Increasingly, medical examiners are using risk factors such as prone sleep position and bed sharing as causes of death, and not assigning SIDS as the cause of death. By emphasizing the "safe" versus "unsafe" sleep environment, the system has the potential to encourage this practice, which has no scientific basis.
Even with the advances in knowledge regarding SIDS, the 1989 NICHD expert panel definition for SIDS and considerations have not changed (5). It is important that we preserve the ability to pursue the causal pathways by not making assumptions regarding the etiology(s) and pathophysiology.
Disclaimer:The views expressed in this letter are those of the author alone; they do not necessarily reflect those of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, the National Institutes of Health, or the US Department of Health and Human Services.
1.Duncan JR, Paterson DS, Hoffman JM, Mokler DJ, Borenstein NS, Belliveau RA, Krous HF, Haas EA, Stanley C, Nattie EE, Trachtenberg FL, Kinney HC. Brainstem serotonergic deficiency in sudden infant death syndrome. JAMA 2010 Feb 3;303(5):430-7. doi: 10.1001/jama.2010.45
2. Matturri L, Lavezzi AM unexplained stillbirth versus SIDS: common congenital diseases of the autonomic nervous system--pathology and nosology. Early Hum Dev. 2011 Mar;87(3):209-15. doi: 10.1016/j.earlhumdev.2010.12.009. Epub 2011 Jan 22
3. Van Nordstrand DW, Aimaki A, Rubinos C, Dolatova E, Srinivas M, Tester DJ, Saffitz JE, Duffy HS, Ackerman MJ. Connexin-43 mutation causes heterogeneous gap junction loss and sudden infant death. Circulation 2012;125:474-481.
4.Randall BB, Paterson DS, Haas EA, Broadbelt KG, Duncan JR, Mena OJ, Krous HF, Trachtenberg FL, Kinney HC. Potential asphyxia and brainstem abnormalities in sudden and unexpected death in infants. Pediatrics 2013;132(6):e1616-25. doi: 10.1542/peds.2013-0700. Epub 2013 Nov 11
5.Willinger M, James LS, Catz C. Defining the Sudden Infant Death Syndrome (SIDS): Deliberations of an expert panel convened by the National Institute of Child Health and Human Development. Pediatr Path. 1991;11:677-684.
Conflict of Interest:
None declared