TABLE 3.
ADDITIVE EFFECT OF EXPOSURES TO CIGARETTE SMOKE AND WOOD SMOKE ON CHRONIC OBSTRUCTIVE PULMONARY DISEASE OUTCOMES (N = 1,861)*
| Exposure Variable | FEV1 % Predicted† |
Airflow Obstruction (GOLD) |
Chronic Bronchitis |
|||
|---|---|---|---|---|---|---|
| PE (SE) | P Value | OR (95% CI) | P Value | OR (95% CI) | P value | |
| Current cigarette smoke only, n = 761 (40.9%) | −0.03 (0.01) | < 0.001 | 1.25 (0.94–1.67) | 0.13 | 3.92 (2.92–5.26) | < 0.001 |
| Wood smoke only, n = 197 (10.6%) | −0.03 (0.01) | 0.001 | 1.70 (1.15–2.49) | 0.007 | 2.12 (1.41–3.18) | < 0.001 |
| Cigarette smoke and wood smoke, n = 318 (17.1%) | −0.06 (0.01) | < 0.001 | 2.71 (1.89–3.89) | < 0.001 | 5.74 (4.05–8.13) | < 0.001 |
Definition of abbreviations: CI = confidence interval; OR = odds ratio; PE = point estimate.
The referent group included those currently exposed to neither smoke (n = 585, or 31.4%). All models were adjusted for sex, age categories, Hispanic ethnicity, obesity (BMI ≥ 30 kg/m2), educational status (at least high school or not), and heavy smoking history (pack-years > 40 or not). Results for absolute postbronchodilator FEV1/FVC ratio and for airflow obstruction defined by NHANES III criterion were similar to those for FEV1 % predicted and airflow obstruction defined by GOLD criterion respectively.
Nonparametric tests using GLM regression models with a Poisson distribution and log link were used to evaluate the continuous FEV1 % predicted outcome and logistic regression models were used for airflow obstruction and chronic bronchitis. Two-way regression analyses showed that multiplicative interactions between wood smoke and cigarette smoke exposures were not significant for any of the above outcome measures (all P ≥ 0.14). However, the effect sizes in row 3 were approximately the sum of the individual effect sizes for rows 1 and 2, indicating an additive effect.