Children’s asthma hospitalizations and relative risk due to nitrogen dioxide (NO 2): Effect modification by race, ethnicity, and insurance status

This study explores the role of race, ethnicity, and insurance status in modifying the effects of air pollution on children’s asthma hospitalizations in Phoenix, Arizona (US) between 2001 and 2003. While controlling for weather, interactions between nitrous dioxide (NO 2) and race, ethnicity, and insurance status are used to predict relative risk for subgroups of children. The generalized logit regression model for nominal categorical data within a multinomial likelihood framework was used. This model is specifically suited to small counts and the reporting of 95% confidence intervals for the odds ratio of hospital admission for one group as compared to another. The odds ratio is known to approximate relative risk for rare events. Several significant findings were found for race, ethnicity, and insurance status as modulators for the effect of NO 2 on children’s risk for asthma hospitalization: (1) children without insurance have 1.4 (95% CI: 1.1–1.8) times higher risk of asthma admissions than those with private insurance at exceedances of 0.02 parts per million (ppm) of NO 2 above the seasonal mean; the same finding holds for children without insurance as compared to those with Medicaid; (2) black children have 2.1 (95% CI: 1.3–3.3) times higher risk of hospitalization than Hispanic children at seasonal mean NO 2 levels, but this disproportionate risk shrinks to 1.7 with exceedances of 0.02 ppm of NO 2 above the seasonal mean. Specific to finding (1) among those children without health insurance, Hispanic children have 2.1 (95% CI: 1.1–3.8) times higher risk of hospitalization than white children. Among all Hispanic children, those without health insurance have 1.9 (95% CI: 1.3–3.0) times greater risk than those with private insurance; the same finding holds for Hispanic children without insurance as compared to Hispanic children with Medicaid. Specific to finding (2), among children with private insurance, the disproportionate risk of black children as compared to Hispanic children is magnified by a factor of 1.3 (95% CI: 1.0–1.8) for exceedances of 0.02 ppm of NO 2 above the seasonal mean. Although we cannot confirm a cause–effect relationship, this analysis suggests that increasing insurance enrollment for all children, and specifically Hispanic children, may reduce their disproportionate risk from exceedances of air pollution. There are few black children in Phoenix, so further studies are needed to investigate the increasing risk of black children wi