190 - Variability in the Use of the Diagnostic Sub-categories of Sudden Unexpected Infant Death

Publication Number: 2183.190

Barbara M. Ostfeld, Rutgers, Robert Wood Johnson Medical School, New Brunswick, NJ, United States; Thomas Hegyi, Rutgers, Robert Wood Johnson Medical School, New Brunswick, NJ, United States

Background: Sudden Unexpected Infant Death (SUID) includes Sudden Infant Death Syndrome (SIDS), Ill-defined and Unspecified Causes (IUC), and Accidental Suffocation and Strangulation in Bed (ASSB). Following a significant decline in the early 1990s after the launch of national risk-reduction campaigns, the overall SUID rate in the U.S. has remained essentially unchanged. However, the relative use of these diagnostic subgroups has shifted markedly: SIDS, formerly the dominant classification, has declined from 71% of all SUIDs in 1999 to 41% in 2023 (CDC WONDER), while the proportions of IUC and ASSB have increased. Geographic variability in SUID rates and subgroup classifications further complicates surveillance, reflecting potential differences in investigation protocols, certification practices, and interpretation of cases without clear biological parameters.

Objective: To evaluate state-level variation in the distribution and relative use of SIDS, IUC, and ASSB classifications, and to identify patterns that may signal diagnostic inconsistency or differing investigative practices.

Design/Methods: Using CDC WONDER’s public access linked birth/infant death data source for 2021–2023, we analyzed the percentage distribution of SUID cases within each state across the three diagnostic subcategories. Thirty-five states reported cases in all three categories at levels that met the criteria for confidentiality.

Results: Nationally, 41% of SUID cases were attributed to SIDS, 31% to IUC, and 28% to ASSB. At the state level, the proportion of cases classified as SIDS ranged from 7% to 73%, IUC from 5% to 78%, and ASSB from 13% to 62%. Among the 35 included states, 17 (48.6%) most frequently used SIDS, 9 (25.7%) most commonly used IUC, and 8 (22.9%) most frequently used ASSB; 2.9% reported equivalent leading categories. These findings demonstrate wide inter-state variability in diagnostic attribution, suggesting inconsistent application of subgroup definitions.

Conclusion(s): Substantial state-to-state variability exists in the classification of SUID cases. Such differences may reflect heterogeneity in death scene investigation, autopsy practices, and coding interpretation rather than biological or epidemiologic divergence. The penetrance of risk-reduction education may be another contributing factor. Addressing the causes of variability could improve the accuracy, comparability, and utility of public health surveillance data.