BACKGROUND: Sudden Unexpected Infant Death (SUID) is the sudden and unexpected death of an infant aged less than 1 year whose cause of death is not apparent before investigation. SUID has been a leading cause of infant mortality (IM) in Washington State for decades, and in 2015 was the second leading cause of death, attributable for 15.5% of IM cases. Despite the prominence of SUID, there are no published statewide classification criteria; As a result, wide variation in SUID diagnosis patterns may exist across the state. We sought to characterize patterns of variability in SUID cause of death coding by year of infant death and county of residence.
METHODS: SUID cases were identified in Washington Department of Health birth certificate and linked infant death datasets using ICD-10 diagnosis codes that identify underlying cause of death. Codes used to identify potential SUID cases were: R75 Sudden Unexpected Infant Death (SIDS), R99 Ill-Defined/Unknown Cause of Death, and W75 Accidental Suffocation and Strangulation in Bed (ASSB). Trends were examined from 2006-2015 using STATA v13.1 and JoinPoint v4.0.4. Records were restricted to Washington State residents at time of infant death.
RESULTS: From 2006 to 2015, the SUID rate in Washington significantly decreased on average -3.22% each year, peaking at 10.4 per 10,000 live births in 2008, and falling to 7.5 per 10,000 in 2015. Over the ten year period, SUID consistently remained the second leading cause of death behind congenital malformations. However, when causes of death are broken out by neonatal and post-neonatal periods, fully 42% of post-neonatal mortality cases are attributable to SUID, making it the leading cause of death for infants older than 27 days and younger than one year. The majority of post-neonatal SUID cases were diagnosed as SIDS cases (79%), followed by ASSB (15%), and ill-defined and unknown cause (6%). The distribution of SUID coding varied widely between counties, apparent in the state’s largest population centers: 92% of SUID cases were coded as SIDS (R95) in King County over this period, compared to just 55% in Pierce County. Wide variance was noted within counties as well, when two five year periods were compared (2006-2010, 2011-2015). Between those two periods, in the state’s third largest county, Snohomish, the proportion of SUID cases coded as SIDS increased from 71% to 92%.
CONCLUSIONS: Administratively-available vital statistics records in Washington show wide variation in the distribution of component SUID codes used over time and across state regions.