Association of short-term exposure to ambient carbon monoxide with hospital admissions in China.

Evidence on the acute effects of ambient carbon monoxide (CO) pollution on morbidity risk in developing countries is scarce and inconsistent. We conducted a multicity case-crossover study in 26 largest cities in China from January, 2014 to December, 2015 to examine the association between short-term exposure to CO and daily hospital admission. We fitted conditional logistic regression to obtain effect estimates of the associations. We also performed subset analyses to explore the health effects of CO at low levels. During the study period, a total of 14,569,622, 2,008,786 and 916,388 all-cause, cardiovascular and respiratory admissions were identified, respectively. A 1 mg/m increase in the CO concentrations corresponded to a 3.75% (95% CI, 3.63-3.87%), 4.39% (95% CI, 4.07-4.70%), and 4.44% (95% CI, 3.97-4.92%) increase in all-cause, cardiovascular, and respiratory admissions on the same day, respectively. The associations were robust to controlling for criteria co-pollutants. In subset analyses, negative effects of short-term CO exposure on hospital admission were observed at lower concentrations (<1 mg/m), while positive effects were observed at higher concentrations (>2 mg/m). In conclusion, current CO levels in China were significantly associated with increased daily hospital admissions.