Measures
ACS was defined by new chest radiograph infiltrate associated
with fever, chest pain, increased work of breathing, or oxygen
desaturation. Single ACS (Yes/No) was defined as only one
admission for ACS throughout the lifetime. Recurrent ACS (Yes/No)
was defined as at least 2 ACS incidents during the lifetime.Severe ACS was defined by admission to the pediatric intensive
care or special care units.
Neighborhood deprivation was assessed with the 2015 Area
Deprivation Index (ADI) for the State of Alabama. The ADI is an existing
factor-based composite measure of socioeconomic deprivation, available
in state-specific (1-10 scale) versions, with higher values indicating
higher deprivation.18,19 The ADI is constructed from
17 variables in the domains of income, education, employment, and
housing quality collected by the American Community Survey and
aggregated to U.S. Census block groups. Neighborhood racial composition
is not a component of the ADI. In this study, each patient was assigned
a neighborhood ADI value according to the Census block group in which he
or she resided based on the current address in their electronic health
record. Because the ADI was not normally distributed, we dichotomized it
as high (ADI 7-10) vs low (ADI 1-6) socioeconomic deprivation.
Neighborhood racial composition was calculated using the count of
African American residents in each Census block group and converting it
to a percentage of the total population count in that block group. The
measure was not normally distributed and was treated as a categorical
variable. As neighborhoods that were ≥90% African American were more
prevalent in the sample than any other category, we dichotomized the
measure as ≥90% vs <90% African American. Alternative
categorization (tertiles and quartiles) produced similar results.
Rurality was assessed with the 2010 Rural-Urban Commuting Area
(RUCA) codes, a classification that combines U.S. Census Bureau
definitions with commuting information and ranks Census tracts on a
scale of 1-10, with higher values indicating higher
rurality.20 We dichotomized the measure as metro vs
non-metro (RUCA scores 1-3 vs ≥4).
Covariates included sex (Male/Female), age, health insurance type
(Public/Private), body mass index (BMI), chronic transfusions (Yes/No),
hydroxyurea (Yes/No), asthma diagnosis (using ICD-10 code or active
asthma treatment in the electronic medical records) (Yes/No), and SCD
phenotype (SS, SB0, SB+, or SC), which was confirmed by hemoglobinopathy
fractionation.