The role of socioeconomic position as an effect-modifier of the association between outdoor air pollution and children's asthma exacerbations: an equity-focused systematic review.

BACKGROUND: The role of socioeconomic position (SEP) as an effect modifier of the association between asthma exacerbations and outdoor air pollution remains unclear.

OBJECTIVE: To identify and summarize the evidence regarding SEP as an effect modifier of the association between asthma exacerbations and outdoor air pollution in children.

METHODS: We conducted searches in five electronic databases from January 1950 to June 2015 with no language restriction. Observational studies involving children, measuring any non-biological outdoor air pollutant exposure, resulting in any asthma-related health service use, and reporting measures of effect by individual or aggregated SEP measures were included.

RESULTS: Ten studies met the inclusion criteria. Five studies reported on hospitalizations, three on emergency department visits, one on ambulatory visits, and one on repeat hospital visits. Six studies identified differential effects of the effect of air pollution on asthma outcomes by SEP with stronger effects for children with a low SEP level; however, the analysis of interaction between air pollutants and SEP was significant in one study of asthma hospitalizations only. The differential effect was reported using individual and aggregated SEP measures.

CONCLUSION: This review reveals that there is weak evidence of SEP as an effect-modifier of the association between air pollution and children's asthma exacerbations. While stronger negative effects on asthma-related hospitalizations occur for children living in a lower SEP, the sample size of some of the original studies limited the statistical assessment of the modification effect.