Sickle Cell Disease Mortality and Census Tract-Level Social Vulnerability – California Sickle Cell Data Collection Program, 2016-2022

Background: Sickle cell disease (SCD) is a rare, genetic disease which impacts the shape and function of red blood cells and affects approximately 100,000 individuals in the United States, mostly African Americans (1 in 365 births). A prior analysis of county-level Social Vulnerability Index (SVI) using newborn screening data across 11 states found that approximately two-thirds of birthing parents of newborns with SCD resided in counties with high or very high social vulnerability. However, substantial variation in social vulnerability within counties warrants analysis at the sub-county level. The California Sickle Cell Data Collection (SCDC) program collects residential address from mortality records, which allows for analysis of SVI at the census tract-level for decedents. The objective of this analysis was to characterize census-tract level SVI for CA residents with SCD who died during the years 2016-2022.

Methods: Mortality records for 2016-2022 were obtained from the California Department of Public Health, and records with a diagnosis code for SCD in any cause of death field were selected for analysis. The decedent’s residential address at time of death was geocoded to determine census tract. Census tract-level SVI percentiles were obtained from the CDC/Agency for Toxic Substances and Disease Registry (ATSDR)’s database for 2022. Percentiles were obtained for overall SVI and four SVI themes: socioeconomic status (e.g., below 150% poverty level), household characteristics (e.g., single-parent households, people with disabilities), racial and ethnic minority status, and housing type and transportation (e.g., crowding, no vehicle). SVI percentiles were categorized by quartile: low (0-25^th percentile), medium (26^th-50^th percentile), high (51^st-75^th percentile) and very high (76^th-100^th percentile). ANOVA testing was used to compare mean overall SVI percentile for decedents by age at death, sex, race, and ethnicity.

Results: During 2016-2022 there were 429 decedents with a residential address in California and a SCD diagnosis code in any field of the death record. Approximately half (51.1%) of decedents were female, 90.2% were Black, and 6.3% were Hispanic/Latino. The median age of death was 49 years (IQR: 24 years). The most common county of residence was Los Angeles (35.7%) followed by Alameda (9.6%), home to the city of Oakland. SCD was listed as the underlying cause of death for 208 deaths (48.5%). Overall, 70.9% of decedents lived in “high” or “very high” SVI census tracts. Findings were similar by SVI theme, with 67.6% in tracts with high vulnerability by socioeconomic status, 64.8% by household characteristics, 74.6% by racial and ethnic minority status, and 66.4% by housing type & transportation. Mean SVI differed significantly by age (p=0.03), with lower SVI among decedents age 0-19 years (mean percentile: 51.0; SD: 31.5) than those age 20-49 years (mean: 66.2; SD: 26.4) or >=50 years (mean: 61.7; SD: 25.9). Mean SVI did not differ significantly by sex, race, or ethnicity.

Conclusions: The findings from this analysis indicate that most individuals with SCD in California live in census tracts with high levels of social vulnerability at the time of death. These findings are consistent with previous analyses performed at the county level. Considered together with the previous findings using newborn screening data, these results suggests that individuals with SCD live in vulnerable community across the lifespan. However, our finding of slightly lower SVI among younger decedents may reflect the challenges young adults with SCD face in transitioning to adult care and securing stable employment and quality housing. Several components of social vulnerability may be targeted for intervention by the healthcare system, including providing transportation to medical care, assistance completing requirements for Medicaid, and high-quality translation services for the growing population of Hispanic/Latino individuals with SCD in California. Further research should be done to assess whether there are differences in healthcare utilization or disease severity for people with SCD living in highly vulnerable communities.