Outdoor air pollution and the risk of asthma exacerbations in single lag0 and lag1 exposure patterns: a systematic review and meta-analysis

Figures & data

Figure 1. The flow chart of article selection.

Table 1. Relationships between air pollutants and asthma exacerbations in overall and quality sensitivity analyses.

Characteristics	Air pollutants (incremental unit)
	AQI (100units)	PM2.5 (10μg/m^3)	PM10 (10μg/m^3)	SO2 (10μg/m^3)	NO2 (10μg/m^3)	CO (1mg/m^3)	O3 (10μg/m^3)
Overall analyses with lag0 exposure^a
Number of the studies	4	27	27	31	28	14	33
RR (95%CI)	1.057(1.011, 1.103)	1.007(1.005, 1.010)	1.009(1.005, 1.012)	1.004(1.000, 1.007)	1.010(1.006, 1.014)	1.030(1.011, 1.048)	1.005(1.002, 1.009)
I^2, %	95.8	80.0	85.1	58.6	68.3	64.3	86.1
Begg’s test, p value	0.308	0.687	0.664	0.026	0.631	0.322	0.015
Egger’s test, p value	0.331	0.061	0.021	0.007	0.519	0.114	0.042
Quality sensitivity analyses with lag0 exposure^a
Number of the studies	3	16	18	19	19	9	23
RR (95%CI)	1.018(0.998, 1.038)	1.007(1.004, 1.010)	1.006(1.003, 1.009)	1.006(0.998, 1.013)	1.009(1.006, 1.013)	1.017(1.002, 1.031)	1.006(1.002,1.010)
I^2, %	78.5	87.7	65.7	72.3	51.8	46.8	90.4
Begg’s test, p value	1.000	0.940	0.889	0.085	0.496	0.917	0.047
Egger’s test, p value	0.837	0.156	0.247	0.072	0.595	0.867	0.066
Overall analyses with lag1 exposure^b
Number of the studies	4	24	27	31	27	17	35
RR (95%CI)	1.064(1.022, 1.106)	1.005(1.002, 1.008)	1.007(1.004, 1.011)	1.003(0.999, 1.006)	1.008(1.004, 1.012)	1.025(1.007, 1.042)	1.010(1.006, 1.013)
I^2, %	96.1	85.6	83.5	56.9	68.2	41.7	86.5
Begg’s test, p value	0.308	0.835	0.253	0.478	0.168	0.124	0.059
Egger’s test, p value	0.252	0.883	0.002	0.088	0.068	0.006	0.008
Quality sensitivity analyses with lag1 exposure^b
Number of the studies	3	18	19	24	20	13	25
RR (95%CI)	1.022(1.000, 1.043)	1.005(1.003, 1.008)	1.006(1.003, 1.009)	1.002(0.998, 1.006)	1.009(1.005, 1.013)	1.011(1.002, 1.020)	1.009(1.005, 1.013)
I^2, %	86.5	85.4	70.3	58.0	62.4	2.0	87.5
Begg’s test, p value	1.000	0.928	0.778	0.333	0.441	0.202	0.116
Egger’s test, p value	0.674	0.989	0.042	0.145	0.052	0.055	0.036

Abbreviations: PM_2.5, particulate matter diameter ≤ 2.5 μm; PM₁₀, particulate matter diameter ≤ 2.5 μm; RR, relative risk.

a lag0 exposure, single lag0 exposure.

b lag1 exposure, single lag1 exposure.

Data availability

Data are available on reasonable request (contact Yan Hu, [email protected]).