Influence of Ultrafine Particles Exposure on Asthma Exacerbation in Children: A Meta-Analysis.

Background: Air pollution is a major cause of asthma exacerbation. Most studies have shown that exposure to coarse and fine particulate matter is associated with asthma exacerbation. Ultrafine particles (UFPs, aerodynamic diameter ≤ 0.1 µm) are the smallest airborne particles, which are capable of penetrating deep into the lungs. Toxicological studies have suggested that exposure to UFPs may have serious effects on respiratory health. However, epidemiological evidence on the effects of UFPs exposure on asthma exacerbation in children remains unclear.
Objective: We conducted a meta-analysis to quantitatively assess the effects of exposure to UFPs on childhood asthma exacerbation.
Methods: We searched four databases for epidemiological studies published until March 20, 2018. Pooled Odds Ratios (OR) and 95% confidence intervals (95% CIs) per 10000 particles/cm3 were estimated using fixed-effect models. Subgroup analyses, sensitivity analyses, and Begg's and Egger's regression were also performed.
Results: Eight moderate-high quality studies with 51542 events in total satisfied the inclusion criteria. Exposure to UFPs showed a positive association with childhood asthma exacerbation [OR (95% CI): 1.070 (1.037, 1.104)], increased asthma-associated emergency department visits [OR (95% CI): 1.111 (1.055, 1.170)], and asthma-associated hospital admissions [OR (95% CI): 1.045 (1.004, 1.088)] and had a stronger association with childhood asthma exacerbation at long lags [OR (95% CI):1.060 (1.039, 1.082)]. A low heterogeneity and no publication bias were detected.
Conclusion: Exposure to UFPs may increase the risk of asthma exacerbation and may be strongly associated with childhood asthma exacerbation at long lags.
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