Unexplained Infant Deaths Without Unsafe Sleep Factors: 2011 to 2020.

Objectives: To describe sudden unexpected infant deaths (SUIDs) occurring in safe sleep environments and explore differences in selected characteristics.

Methods: We examined SUID from 22 jurisdictions from 2011 to 2020 and classified them as unexplained, no unsafe sleep factors (U-NUSF). Data were derived from the Sudden Unexpected Infant Death and Sudden Death in the Young Case Registry, a population-based Centers for Disease Control and Prevention surveillance system built on the National Center for Fatality Review and Prevention's child death review program. SUID classified as U-NUSF included infants who were (1) awake, under supervision, and witnessed to become unresponsive or (2) found unresponsive in a safe sleep environment after sleep (unwitnessed). We calculated frequencies and percentages for demographics, birth and environmental characteristics, medical history, and death investigation findings.

Results: Most of the 117 U-NUSF SUID occurred before 4 months of age. Witnessed deaths most commonly occurred at <1 month of age (28%), whereas unwitnessed deaths most commonly occurred at ages 2 to 3 months (44%) Among all U-NUSF, 69% occurred in the infant's home (62% witnessed, 77% unwitnessed). All unwitnessed deaths occurred in a crib; most witnessed deaths occurred while being held (54%) or in a car seat traveling (18%). Most infants (84%) had no history of abuse or neglect. Abnormal autopsy findings were reported in 46% of deaths (49% witnessed, 42% unwitnessed).

Conclusions: Characterizing these deaths is key to advancing our knowledge of SUID etiology. Our study revealed a heterogeneous group of infants, suggesting physiologic, genetic, or environmental etiologies.