Systematic Methods to Select and Review Epidemiological Literature on the Health Effects of Long-term Exposure to TRAP

Abstract

BACKGROUND AND AIM: The health effects of traffic-related air pollution (TRAP) continue to be of important public health interest. Following its well-cited 2010 critical review, HEI appointed a new expert Panel to review the literature on the health effects of long-term exposure to TRAP. METHODS: The Panel followed a systematic protocol they published in Prospero to search the literature, assess study quality, summarize results, and reach conclusions about the body of evidence. An extensive search was conducted of literature published between January 1980 and July 2019 on selected health outcomes (all-cause and cause-specific mortality, respiratory effects, cardiometabolic effects, and adverse birth outcomes). The Panel considered studies both within and outside the near-road environment because traffic contributes to ambient air pollution at neighborhood and urban scales. They developed a framework of exposure to TRAP to guide transparent selection and evaluation of epidemiological studies. Criteria including the pollutant considered, spatial scale, and exposure assessment methods were used to identify studies in which the exposure contrasts were related primarily to traffic emissions. RESULTS:Meta-analyses were performed in cases where three or more studies were identified for the same exposure and health outcome. Conclusions were based on a modified US National Toxicology Program’s Office of Health Assessment and Translation (OHAT) approach and a narrative assessment. The two approaches were considered equally valuable in the Special Report, reflecting the complex issues in determining the level of confidence. CONCLUSIONS:The review is now well underway, and the methods along with lessons learned during their application will be presented. The systematic review will undergo peer-review, and publication is aimed for late 2021. The new review will be an authoritative update of HEI’s most-cited report for use by researchers and policymakers. KEYWORDS: traffic-related air pollution, systematic review, birth outcomes, cardiometabolic effects, respiratory effects, mortality