Table 5

Subgroup analyses for prevalent chronic bronchitis and cough and sputum symptoms at baseline, per IQR increase in each pollutant

Cases/non-cases (n/n)Adjusted* OR (95% CI)
PM2.5 NO2 Black carbon
Females
 Chronic bronchitis4070/73 2101.03 (0.99 to 1.08) 1.08 (1.03 to 1.13) 1.08 (1.04 to 1.13)
 Usual sputum7268/69 987 1.05 (1.02 to 1.08) 1.08 (1.04 to 1.12) 1.08 (1.05 to 1.11)
 Chronic cough5384/71 9241.03 (0.99 to 1.07) 1.07 (1.03 to 1.11) 1.08 (1.04 to 1.11)
 Usual cough11 194/65 731 1.04 (1.02 to 1.07) 1.09 (1.06 to 1.12) 1.09 (1.06 to 1.12)
Age >=50
 Chronic bronchitis2669/37 6390.98 (0.94 to 1.03)0.99 (0.94 to 1.05)1.03 (0.98 to 1.09)
 Usual sputum4104/36 1621.01 (0.98 to 1.06)1.01 (0.97 to 1.06)1.03 (0.99 to 1.08)
 Chronic cough2999/37 3330.99 (0.94 to 1.03)1.02 (0.97 to 1.08) 1.06 (1.01 to 1.11)
 Usual cough5457/36 6061.01 (0.97 to 1.04) 1.05 (1.01 to 1.09) 1.06 (1.02 to 1.10)
No post-secondary education
 Chronic bronchitis6120/85 5421.00 (0.96 to 1.03) 1.06 (1.02 to 1.10) 1.07 (1.03 to 1.11)
 Usual sputum10 293/81 3401.02 (0.99 to 1.05) 1.07 (1.04 to 1.10) 1.08 (1.05 to 1.11)
 Chronic cough7427/84 2961.00 (0.97 to 1.03) 1.04 (1.00 to 1.08) 1.06 (1.03 to 1.10)
 Usual cough14 625/76 626 1.03 (1.01 to 1.06) 1.08 (1.05 to 1.11) 1.08 (1.06 to 1.11)
Never smokers
 Chronic bronchitis2960/59 9351.03 (0.98 to 1.08) 1.09 (1.03 to 1.14) 1.07 (1.02 to 1.12)
 Usual sputum5426/57 441 1.05 (1.02 to 1.09) 1.10 (1.06 to 1.14) 1.08 (1.05 to 1.12)
 Chronic cough3472/59 4561.04 (1.00 to 1.09) 1.05 (1.01 to 1.11) 1.06 (1.02 to 1.11)
 Usual cough8115/54 585 1.07 (1.04 to 1.10) 1.09 (1.06 to 1.13) 1.08 (1.05 to 1.11)
Asthmatics
 Chronic bronchitis1781/98310.99 (0.92 to 1.05)1.03 (0.96 to 1.11)1.04 (0.97 to 1.11)
 Usual sputum2820/8802 1.10 (1.04 to 1.16) 1.12 (1.06 to 1.19) 1.12 (1.07 to 1.19)
 Chronic cough2039/95891.04 (0.97 to 1.10)1.05 (0.98 to 1.12)1.07 (1.01 to 1.14)
 Usual cough3362/8209 1.06 (1.00 to 1.11) 1.08 (1.02 to 1.14) 1.10 (1.04 to 1.15)
  • Statistically significant results are shown in bold.

  • *Model adjusted for sex, age, educational attainment (low: junior secondary/lower vocational or less, medium: senior secondary/secondary vocational, high: higher vocational/university), BMI (continuous), smoking status (never, ex, current), pack-years smoking and environmental tobacco smoke at home. IQR for PM2.5=1.30 µg/m3, for NO2=6.92 µg/m3 and for BC=0.29 x 10−5 m−1.

  • BC, black carbon; BMI, body mass index; NO2, nitrogen dioxide; PM2.5, particulate matter with a diameter of less than 2.5 µm.