Characteristics of study participants at baseline (1981) and end of follow-up (2011)
| 1981 | 2011 | |||
|---|---|---|---|---|
| Silk (n=472) | Cotton (n=447) | Silk (n=291) | Cotton (n=296) | |
| Male | 200 (42.4%) | 214 (47.9%) | 112 (38.5%) | 122 (41.2%)* |
| Age, years | 36.7±10.7 | 37.8±10.6 | 65.8±9.7 | 65.6±9.9 |
| Follow-up time, years | – | – | 29.4±0.07 | 29.6±0.06 |
| Height, cm | 162.5±7.3 | 163.9±7.5* | 160.6±7.6 | 162.1±7.9 |
| Current smoking | 118 (25.0%) | 159 (35.6%)* | 60 (20.6%) | 66 (22.3%) |
| Male | 117 (58.5% of males) | 149 (69.6% of males) | 59 (52.7% of males) | 63 (51.6% of males) |
| Female | 1 (0.9% of females) | 10 (2.2% of females) | 1 (0.6% of females) | 3 (1.7% of females) |
| Pack-years† | 9.2±10.0 | 8.5±9.8 | 28.2±19.8) | 28.2±19.0 |
| Lifetime non-smoker | 348 (73.7%) | 284 (65.5%)* | 182 (66.9%) | 178 (62.9%) |
| Male | 77 (38.5% of males) | 61 (28.5% of males) | 22 (20.2% of males) | 25 (20.8% of males) |
| Female | 271 (99.6% of females) | 223 (95.7% of females) | 160 (98.2% of females) | 153 (93.9% of females) |
| Active textile work | 472 (100%) | 447 (100%) | 2 (0.34%) | 1 (0.17%) |
| Years employed | 16.2±11.3 | 16.2±10.3 | 27.3±9.2 | 26.3±8.0 |
| Years since retirement‡ | – | – | 18.5±4.5 | 17.8±5.2 |
| Cumulative endotoxin exposure, EU/m3-years§ | – | 11 540 (3442–32 111) | – | 38 928 (17 030–65 204) |
| FEV1, litres | 2.84±0.67 | 2.90±0.72 | 2.29±0.58 | 2.28±0.64 |
| Per cent predicted FEV1¶ | 99.6±13.1 | 100.2±13.9 | 107.7±18.9 | 104.4±18.9 |
| FEV1/FVC ratio | 0.84±0.09 | 0.83±0.09 | 0.77±0.08 | 0.76±0.08 |
| FEV1/FVC<0.7** | 20 (4.2%) | 27 (6.0%) | 39 (13.4%) | 40 (13.5%) |
| FEV1 ≥80% predicted | 12 | 16 | 31 | 30 |
| 50% ≤FEV1 <80% predicted | 7 | 10 | 7 | 7 |
| 30% ≤FEV1 <50% predicted | 1 | 1 | 1 | 2 |
| FEV1 <30% predicted | 0 | 0 | 0 | 1 |
| Unadjusted annual FEV1 change (mL/year) | – | – | −19.6±12.1 | −23.0±12.9* |
| Chronic bronchitis | 36 (7.6%) | 96 (21.5%)* | 22 (2.6%) | 29 (4.9%) |
| Chronic cough | 33 (7.0%) | 87 (19.5%)* | 7 (1.2%) | 11 (1.9%) |
| Dyspnoea on exertion | 18 (3.8%) | 67 (15.0%)* | 71 (12.1%) | 67 (11.4%) |
| Byssinosis | 0 (0%) | 34 (7.6%)* | 0 (0%) | 0 (0%) |
Continuous variables are presented as mean±SD or median (IQR). Categorical variables are presented as n (%).
*p<0.05.
†Calculated among ever-smokers only.
‡Calculated among retired workers only.
§A limited number of full shift samples taken in silk mills were found to have undetectable levels of endotoxin by the limulus amoebocyte lysate assay. Thus, silk workers were considered unexposed to endotoxin.
¶Prediction equations derived from the Chinese reference population.18
**Pre-bronchodilator spirometry. FEV1, forced expiratory volume in 1 s; FVC, forced vital capacity.