INTRODUCTION
Preterm birth accounts for approximately 10% of live births in the
United States annually and is a leading cause of mortality in children
less than five years of age worldwide.1 Among infants
born preterm, the most common serious complication is bronchopulmonary
dysplasia (BPD), with almost 50,000 infants estimated to be diagnosed in
the US annually.2 Although most infants with BPD will
wean from respiratory support during the first few years of
life,3 up to 50% will be re-hospitalized during that
same period for pulmonary exacerbations, with many going on to develop
asthma and asthma-like symptoms.4 Respiratory symptoms
and abnormalities on pulmonary function testing, including chronic
obstructive pulmonary disease, have been shown to persist into
adulthood.5
With increasing numbers of preterm infants surviving into childhood and
adulthood, identifying modifiable socio-environmental factors that
influence long-term health outcomes in the outpatient setting may help
optimize long-term clinical outcomes.6 In particular,
factors that increase respiratory inflammation (such as infections,
tobacco exposure, poor air quality, etc.) have been associated with
worse lung function trajectories in patients with
BPD.7,8 Socioeconomic disparities may expose certain
infants and children to more of these risk factors. While individual
risk factors can be assessed in isolation, many risk factors are
co-related, with a potentially cumulative effect. Composite indices of
socioeconomic disadvantage may allow for assessment of the cumulative
risk associated with exposure to multiple community-level factors.
Various country-specific indices been used in previous studies to
evaluate relationships between socioeconomic status and pediatric health
outcomes,9 with significant associations being
reported in a number of studies spanning several countries. Increased
neighborhood deprivation has been shown to increase a child’s risk of
fractures,10,11 obesity,12 abusive
head trauma,13 and infant
mortality.14 It has also been associated with worse
outcomes for children with appendicitis,15asthma,16-18 cystic fibrosis,19diabetes,20 acute lymphoblastic
leukemia,21 and after liver and kidney
transplantation.22,23 In the United States, the Area
Deprivation Index (ADI) measures the socioeconomic context of census
block groups, which correspond to neighborhoods. The index is composed
of 17 factors, including income, education, housing, and
employment.9
Although previous research in BPD has evaluated outcomes based on single
risk factors (e.g., insurance status),24,25 a recent
French study showed that patients with BPD living in neighborhoods with
high socioeconomic disadvantage had a three-fold higher risk of
respiratory hospitalization compared to those living in affluent
neighborhoods.26 A similar study has not yet been
conducted in the United States. We hypothesized that greater
neighborhood deprivation as quantified by the ADI would be associated
adverse respiratory outcomes in a U.S. regional registry of infants and
young children with BPD.