Ambient Carbon Monoxide and Daily Mortality: A Global Time-Series Study in 337 cities

Abstract

Background Epidemiological evidence on the short-term association between ambient carbon monoxide (CO) and mortality is inconclusive and limited to single cities, regions, or countries. Generalization of results from previous studies is challenged by potential publication bias and different modeling approaches. We, therefore, assessed the associations between short-term exposure to CO and daily mortality in a multi-city multi-country setting.Methods We collected daily data on air pollution, meteorology, and total mortality from 337 cities in 18 countries from the Multi-Country Multi-City Collaborative Research Network. We first estimated city-specific associations using confounder-adjusted generalized additive models with a quasi-Poisson distribution; then, we pooled the estimates using a random-effects multilevel meta-analytical model. We also assessed the overall shape of the exposure-response curve and evaluated the existence of a threshold value.Results Overall, a 1 mg/m3 increase in the average CO concentration of the previous day was associated with a percent increase of 0.91% (95% confidence interval [95% CI]: 0.32%, 1.50%) in daily total mortality. The pooled exposure-response curve showed a continuously elevated mortality risk with increasing CO concentrations, suggesting no evidence for a threshold. Larger mortality risk estimates were found at daily CO levels below 1 mg/m3 and persisted at concentrations as low as below 0.2 mg/m3.Conclusions This international study is, to our knowledge, by far the largest epidemiological study on short-term CO-related mortality. We found significant associations between short-term exposure to ambient CO and daily mortality, even at levels well below the current global and national air quality guidelines.The study was conducted on behalf of the MCC Collaborative Research Network