Air pollution interventions and respiratory health: a systematic review

BACKGROUND: Indoor and ambient air pollution exposure is a major risk to respiratory health worldwide, particularly in low- and middle-income countries (LMICs). Interventional trials have mainly focused on alternatives to cooking stoves, with mixed results. Beyond cooking, additional sources of particulate matter also contribute to the burden of air pollution exposure. This review explores evidence from current randomised controlled trials (RCTs) on the clinical effectiveness of interventions to reduce particulate matter in LMICs. METHODS: Twelve databases and the grey literature (e.g., Government reports and policy papers) were searched. Eligible studies were RCTs conducted in LMICs aiming to reduce particulate exposure from any source and reporting on at least one clinical respiratory outcome (respiratory symptoms, lung function or clinical diagnoses). Data from relevant studies were systematically extracted, the risk of bias assessed and narrative synthesis provided. RESULTS: Of the 14 included studies, 12 tested 'improved' cookstoves, most using biomass, but solar and bioethanol cookers were also included. One trial used solar lamps and another was an integrated intervention incorporating behavioural and environmental components for the treatment and prevention of chronic obstructive pulmonary disease. Of the six studies reporting child pneumonia outcomes, none demonstrated significant benefit in intention-to-treat analysis. Ten studies reported respiratory symptom outcomes with some improvements seen, but self-reporting made these outcomes highly vulnerable to bias. Substantial inter-study clinical and methodological heterogeneity precluded calculation of pooled effect estimates. CONCLUSION: Evidence from the RCTs performed to date suggests that individual household-level interventions for air pollution exposure reduction have limited benefits for respiratory health. More comprehensive approaches to air pollution exposure reduction must be developed so their potential health benefits can be assessed.