Characteristics of Sudden Unexpected Infant Deaths — United States, 2020–2024

Abstract

Sudden unexpected infant death (SUID) accounts for approximately 3,400 deaths among infants aged <1 year in the United States annually. To reduce SUID risk, the American Academy of Pediatrics recommends that infants be placed to sleep supine on a flat, firm, nonshared surface, without soft bedding. SUID vital statistics data do not include details on sleep environment and other contextual factors that are critical for SUID surveillance and prevention. CDC’s SUID and Sudden Death in the Young Case Registry (case registry) helps fill this gap. The case registry, a multijurisdictional, population-based active surveillance system, builds on child death review programs, compiling detailed information on deaths in persons aged 0–18 years from multiple data sources. CDC analyzed 2020–2024 case registry data to describe 1) SUID by sociodemographic and sleep environment characteristics, 2) the case registry classification algorithm SUID categories, and 3) death investigation components. Among the 4,861 SUIDs included in this analysis, most decedents were aged 0–3 months, male, Black or African American or White, born full-term, and insured by Medicaid. Unsafe sleep factors were present in at least three fourths of SUIDs. Almost all infants had an autopsy and death investigation, although completed components varied. This newly reported, detailed case registry information can be used by public health professionals and clinicians to improve death investigations, increase understanding of etiologies and risk factors, and enhance focused prevention efforts to reduce SUIDs.

Introduction

Sudden unexpected infant death (SUID) includes sudden infant death syndrome (SIDS), accidental suffocation and strangulation in bed, and unknown causes of death. SUID accounts for approximately 3,400 deaths in infants (children aged <1 year) in the United States annually and disproportionately affects Black or African American (Black) and American Indian or Alaska Native infants. (Persons of Hispanic or Latino [Hispanic] origin might be of any race but are categorized as Hispanic; all racial groups are non-Hispanic.) To reduce SUID risk, the American Academy of Pediatrics (AAP) recommends that infants be placed to sleep supine on a flat, firm, nonshared sleep surface (i.e., crib or bassinet [crib]), without soft bedding (1). National vital statistics data demonstrate declines in SUID rates (number of SUIDs per 100,000 live births) during the 1990s, from 154.6 in 1990 to 93.9 in 1999. These declines were attributed to clinical guidance and public health campaigns about safe infant sleep practices (1); however, progress has stalled, and from 2020 to 2022, SUID rates increased from 92.9 to 100.9.

Vital statistics data are best for monitoring national SUID rates and exploring information available on birth and death certificates. However, they lack details about death circumstances and often do not contain sufficient information to determine SUID subtype (e.g., explained versus unexplained deaths) (2). CDC’s SUID and Sudden Death in the Young (SDY) Case Registry (case registry) aims to fill this gap. The case registry, which began with five jurisdictions in 2009, currently includes 32 jurisdictions and captures approximately two in five U.S. SUIDs. The case registry is a multijurisdictional, population-based, active surveillance system that compiles detailed information on sudden deaths in persons aged <20 years from multiple data sources, extending beyond publicly available information (e.g., vital statistics). The case registry builds on existing child death review programs* and uses the Health Resources and Services Administration and CDC-supported National Center for Fatality Review and Prevention’s Pediatric National Fatality Review – Case Reporting System. A multidisciplinary child death review team reviews each SUID and develops case-specific prevention recommendations that are used with compiled data to guide SUID prevention locally and statewide. In addition, every SUID is categorized using a CDC-developed classification algorithm to differentiate explained from unexplained deaths, account for incomplete investigation information, and document whether unsafe sleep factors contributed to the death (2). This report describes 2020–2024 case registry SUID data, not previously published or available through vital statistics alone, building on previous evidence (2–6) to improve understanding and prevention of SUID.

Methods

Data Source

SUIDs^† that occurred during 2020–2024 among residents of 31 jurisdictions^§ participating in the case registry and that met case registry data quality criteria (4,861) were included in this analysis.

Analysis

A descriptive analysis was conducted. SAS (version 9.4; SAS Institute) was used to calculate frequencies and percentages of sociodemographic characteristics, sleep environment characteristics, classification categories (2), and investigation components. This activity was reviewed by CDC, deemed not research, and conducted consistent with applicable federal law and CDC policy.^¶

Results

Characteristics of SUIDs

Among 4,861 case registry SUIDs that occurred during 2020–2024 and met case registry data quality criteria, most involved infants who were aged 0–3 months (66%), male (57%), Black (38%) or White (37%), born at full term (≥37 weeks’ gestation) (74%), and insured by Medicaid (69%) (Table 1). Infants’ sleep environment at death frequently involved unsafe sleep factors that were not mutually exclusive, including 46% of infants who were found in a nonsupine position, 75% on a sleep surface other than a crib, 78% with soft bedding, and 59% sharing a sleep surface. Full airway obstruction (nose and mouth, neck, or chest) was documented in 28% of SUIDs.

Categorization of SUIDs

Using categories from the case registry classification algorithm (Box) (2), the analysis categorized SUIDs as follows: unexplained–no autopsy or death investigation (57; 1%), unexplained–incomplete case information (1,139; 23%), unexplained–no unsafe sleep factors (117; 2%), unexplained–unsafe sleep factors (no or unknown airway obstruction) (2,126; 44%), unexplained–possible suffocation with unsafe sleep factors (503; 10%), and explained–suffocation with unsafe sleep factors (919; 19%) (Table 2). Most SUIDs (3,548; 73%) were classified in a category indicating that unsafe sleep factors (1) were identified in the sleep environment; unsafe sleep factors might also have been present in the unexplained–no autopsy or death investigation and unexplained–incomplete case information categories. Among explained–suffocation, attributed (nonmutually exclusive) mechanisms included soft bedding (obstruction of the infant’s airway by soft objects or loose bedding in the immediate sleep environment) (681; 74%), overlay (obstruction of the infant’s airway by a person or animal) (223; 24%), wedging (obstruction of the infant’s airway resulting from being trapped between two inanimate objects) (69; 8%), or other (obstruction of the infant’s airway by something else in the sleep environment) (33; 4%).

SUID Death Investigation

Overall, among SUIDs in the case registry, 4,779 (98%) had an autopsy and 4,751 (98%) had a death investigation, including toxicology testing (4,613; 95%); imaging (4,311; 89%); microbiology, histology, or pathology testing (4,649; 96%); and death scene re-creation** with the person who found the infant unresponsive (2,418; 50% [90% of re-creations made use of a doll]) (Table 2). Genetic testing was not documented for 86% of infants. Information was missing or unknown regarding the position in which the infant was found for 15% of SUIDs and regarding airway obstruction status for 33% (Table 1).

Discussion

Findings from this analysis of the most recent SUID case registry data are consistent with previously reported findings of sociodemographic and sleep environment characteristics, classification categories, and completed investigation components (2–6). Case registry data can offer insight into the drivers of persistent SUID rates that vital statistics data alone cannot. Continued use of recent case registry data is critical to improving death investigations, increasing understanding of SUID etiologies and risk factors, and providing contextual information for SUID prevention efforts.

Case registry data on the thoroughness of autopsies and death scene investigations, reflected in the unexplained–incomplete case information category (23%), can identify areas for improvement and support engagement with medicolegal communities. Consistent with previous case registry analyses (3), this analysis found that nearly all case registry SUIDs during 2020–2024 had an autopsy (98%) and scene investigation (98%), and critical autopsy components (e.g., toxicology, imaging, or pathology) were typically completed. However, completeness of critical contextual information varied, including information regarding the position in which the infant was found and presence or absence of airway obstruction. Approximately one half of investigations had a documented death scene re-creation, conducted by investigators, with the witness present, to capture circumstances at death. Use of a doll during re-creation to assist witnesses in demonstrating the exact position in which the infant was found increased from 37% during 2010–2012 to 45% in this analysis (3). Although room for improvement remains, this increase might reflect case registry efforts to improve death investigations.

Approximately one half of SUIDs were categorized as unexplained–unsafe sleep factors or unexplained–possible suffocation with unsafe sleep factors. More complete information on airway obstruction status would improve differentiation between explained sleep-related suffocation, with clear prevention implications, and unexplained death for which further investigation of etiologies and risk factors are needed.

The small but heterogeneous unexplained–no unsafe sleep factors category might reflect physiologic or genetic etiologies or those unrelated to the sleep environment (4). In addition, approximately one third of SUIDs had documentation of an unobstructed airway, again suggesting an etiology unrelated to suffocation. These findings underscore the ongoing need to investigate contributing factors that are unrelated to the sleep environment and expand diagnostic evaluation of SUIDs, including relevant genetic testing during autopsy.

Case registry data have previously indicated that unsafe sleep factors increase the risk for explained sleep-related suffocation and unexplained death (5). Most SUIDs in this analysis, regardless of whether they were explained or unexplained, had unsafe sleep factors present, and approximately one fifth were categorized as explained–suffocation. The ≥73% prevalence of unsafe sleep factors identified among SUIDs in this analysis was similar to that reported for 2011–2020 (≥76%) (6). Compared with live infants in the 2016 Pregnancy Risk Assessment Monitoring System (7), SUID cases less frequently met AAP’s safe sleep recommendations, reinforcing the importance of safe sleep practices to reduce SUID risk.

Although safe sleep recommendations^†† are widely promoted, supporting caregivers in implementing recommended practices can be complex. SUIDs differ by race and ethnicity, and Medicaid coverage was overrepresented among SUIDs in the analysis compared with 2020–2024 births among case registry jurisdictions (69% versus 39%).^§§ State or local case registry data analyses can identify prevalent risk factors, populations at high risk for SUID, and contextual contributors (e.g., parental unemployment or housing instability) to guide development and implementation of focused prevention efforts (8). CDC supports the development of such community-based, data-guided SUID prevention efforts in 10 case registry jurisdictions. These jurisdictions use local data, engage with families and providers in their communities, identify locally relevant barriers to and facilitators for practicing safe infant sleep, and develop tailored strategies to increase adoption of safe sleep practices (9).

Limitations

The findings in this report are subject to at least four limitations. First, case registry data are subject to availability, accuracy, and biases in primary data sources, including caregiver and investigator accounts of often unwitnessed events and chaotic death scenes. This might result in higher percentages of missing and unknown responses to some critical variables. Second, social desirability bias might result in underreporting of unsafe sleep practices (10), which could lead to underrepresentation of unsafe sleep factors among SUIDs. Third, although reporting of most variables was >95% complete; variables with >5% missing or unknown responses warrant cautious interpretation, because incomplete information might affect validity and generalizability of reported data. Finally, the study population comprised SUIDs in 31 participating case registry jurisdictions which accounted for approximately 40% of U.S. SUIDs. Thus, study results are not fully generalizable limits generalizability to other jurisdictions and nationally; however, sociodemographic characteristics of the case registry population were similar to characteristics of all U.S. SUIDs.

Implications for Public Health Practice

Public health professionals and clinicians can use newly reported case registry data to improve death investigations, increase understanding of etiology and risk factors, and enhance prevention efforts. Improving the completeness of death investigations, including performing genetic testing and documenting airway obstruction status, can better distinguish deaths with clear prevention implications. SUIDs with no unsafe sleep factors present at the time of death highlight the need to explore additional risk factors and underlying etiologies. Continued analysis and dissemination of up-to-date case registry data offer a more relevant reflection of current practice, which might more effectively guide SUID understanding and prevention.