Table 4

Prevalent chronic bronchitis and cough and sputum symptoms at baseline per IQR increase in each pollutant

All participantsCases/non-cases (n/n)Adjusted* OR (95% CI)
PM2.5 NO2 Black carbon
Chronic bronchitis8128/124 4671.01 (0.98 to 1.04) 1.05 (1.02 to 1.08) 1.06 (1.03 to 1.09)
Usual sputum13 687/118 704 1.04 (1.01 to 1.06) 1.07 (1.04 to 1.10) 1.07 (1.04 to 1.09)
Chronic cough9754/122 9151.00 (0.97 to 1.03)1.03 (1.00 to 1.06) 1.05 (1.02 to 1.08)
Usual cough19 564/112 409 1.03 (1.01 to 1.05) 1.07 (1.05 to 1.09) 1.07 (1.05 to 1.09)
  • 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=0.29×10−5 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.