Table 4.

Multivariate Analysis of Association Between 8-Hour Time-Weighted Average Endotoxin and Quantitative Small Airway Measures

8-Hour TWA Endotoxina (EU/m3)	Exp−856	P Value	E/I MLA	P Value	RVC−856 to −950	P Value	Residual−856	P Value
All (N = 404)
Survey year 2011
≤ 50
50-1,500	–0.014	.431	0.002	.787	0.006	.778	–0.002	.901
1,500-2,300	0.009	.691	0.022	.040	0.066	.011	0.028	.159
2,300-3,900	–0.013	.535	–0.010	.333	–0.010	.693	–0.016	.421
> 3,900	–0.007	.765	0.009	.411	0.024	.380	0.013	.538
Survey year 2016
≤ 50
50-1,500	–0.001	.972	0.008	.354	0.023	.255	0.010	.547
1,500-2,300	0.019	.390	0.023	.035	0.071	.006	0.033	.100
2,300-3,900	0.014	.525	–0.003	.754	0.009	.719	0.012	.532
> 3,900	0.001	.972	0.021	.070	0.051	.060	0.028	.181
Difference
≤ 50
50-1,500	0.013	.435	0.006	.507	0.018	.385	0.012	.487
1,500-2,300	0.010	.634	0.001	.948	0.005	.842	0.005	.823
2,300-3,900	0.027	.193	0.007	.508	0.019	.444	0.028	.171
> 3,900	0.008	.723	0.011	.298	0.028	.289	0.015	.472
Cotton workers (n = 178)
Survey year 2011
≤ 50
50-1,500	0.033	.412	0.039	.036	0.087	.060	0.055	.126
1,500-2,300	0.057	.179	0.059	.003	0.144	.003	0.087	.023
2,300-3,900	0.033	.453	0.030	.143	0.080	.107	0.042	.276
> 3,900	0.046	.302	0.052	.013	0.113	.027	0.075	.063
Survey year 2016
≤ 50
50-1,500	0.052	.202	0.050	.008	0.114	.014	0.075	.038
1,500-2,300	0.072	.091	0.064	.001	0.159	.001	0.099	.010
2,300-3,900	0.065	.137	0.041	.041	0.109	.028	0.079	.044
> 3,900	0.057	.208	0.067	.001	0.149	.004	0.097	.018
Difference
≤ 50
50-1,500	0.019	.602	0.010	.520	0.028	.492	0.020	.560
1,500-2,300	0.015	.692	0.005	.756	0.015	.728	0.012	.732
2,300-3,900	0.032	.386	0.012	.484	0.030	.484	0.036	.312
> 3,900	0.011	.773	0.016	.363	0.036	.393	0.022	.545

Coefficients and P values from the linear mixed model with a random intercept are reported. P < .05 was considered significantly different from zero. Small airway disease quantified by small airway measures was the outcome, and 8-h TWA endotoxin was the exposure variable in the model. The linear mixed models were adjusted for age, sex, height, smoking intensity, survey year, and the interaction between 8-h TWA endotoxin and survey year (8-h TWA endotoxin × survey year). E/I MLA = expiratory-to-inspiratory ratio of mean lung attenuation; Exp₋₈₅₆ = percentage of voxels with attenuation less than -856 HU on expiratory CT scans; HU = Hounsfield unit; pp FEV₁ = percent predicted FEV₁; Residual_–856 = residuals from the linear regression of Exp₋₈₅₆ on the percentage of voxels with attenuation less than –950 HU; RVC_{−856 to −950} = relative volume change in voxels with attenuation between –856 HU and –950 HU; TWA = time-weighted average.

^a50 EU/m³ represents the reference level. 1,500 EU/m³ is the 40th percentile, 2,300 EU/m³ is the 60th percentile, and 3,900 EU/m³ is the 80th percentile. There are 237 textile workers exposed to ≤ 50 EU/m³ endotoxin, 61 workers exposed to 50 to 1,500 EU/m³ endotoxin, 35 workers exposed to 1,500 to 2,300 EU/m³ endotoxin, 37 workers exposed to 2,300 to 3,900 EU/m³ endotoxin, and 34 workers exposed to more than 3,900 EU/m³.