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.