Chronic Obstructive Pulmonary Disease

Steven Markowitz, Problem-Based Exercises for Environmental Epidemiology,

Office of Global and Integrated Environmental Health, World Health, WHO/EHG/98.2, Geneva, 1998, 43-53.

Salvi & Barnes. Chronic obstructive pulmonary disease in non-smokers. Lancet 2009; 374: 733-43

Proportion of patients with chronic obstructive pulmonary disease (COPD) who are non-smokers worldwide.

Question 1. What are some of the other known or suspected causes of COPD?

– Genetic conditions, such as alpha1 anti-tripsin deficiency – Occupational exposures– Ambient air pollution– Environmental tobacco smoke

Salvi & Barnes. Lancet 2009; 374:733

Proportion of households using biomass fuel for cooking worldwide

Question 2. What study design could be used to study this question? Which would you choose?

– Case control study given:• Exploratory nature of study• Long latency of COPD• Difficulty in finding cohorts that differ only (or principally) by type of

cooking fuel• Limited expense and resources needed

Question 3. How would you select controls?– Controls selected from inpatient surgical and gynecological services

and general medical outpatient clinics – Matched on ae and hospital– Excluded if they had history of COPD or Lung Cancer– All underwent lung function testing

Question 4. How would you assess the exposure of cases and controls to indoor smoke?

• Note: need to assess both current and historical smoke exposure• Questionnaire:

– Type of cooking fuel– Dwelling construction– Number of rooms– Location of cooking stove

(same or separate building)– Hours pent per day cooking

• Home visits:– Validate information from questionnaire for current exposure

• Personal monitoring?– Current exposure only

Question 5. What other exposures would you like to gather information on? How would you do it?

• Potential confounders or effect modifiers:– Cigarette smoking– Environmental tobacco smoke– Occupational exposures– Outdoor air pollution– Genetic factors (family history)

Question 6. Should the investigators collect more cases and/or controls? Is it likely they will be able to address all the variables of interest?

VariableNumber of cases with

exposureNumber of controls with

exposure

History of cigarette smoking 43 25

History of husband smoking in home 47* 28**

Used wood as cooking fuel 88 64

Used gasoline as cooking fuel 54 70

*of 96 cases who provided information on husband's smoking**of 88 controls who provided information on husband's smoking

Question 7. Set up the appropriate 2 x 2 tables and calculate the relative risk and 95% confidence interval. Interpret you findings.

Yes NoCigarette Yes 43 25 68Smoking No 61 79 140 OR = 2.23 ( 1.18 4.04 )

104 104 208 p= 0.0078

Husband Yes 47 28 75Smokes No 49 60 109 OR = 2.06 ( 1.08 , 3.93 )

96 88 184 p= 0.0181

Cook with Yes 88 64 152Wood No 16 40 56 OR = 3.44 ( 1.70 , 7.14 )

104 104 208 p= 0.0002

Question 8. How do you interpret these results?

Wood use as cooking fuel Case Control% Reporting wood as fuel (no.)

85% (88) 62% (64)

Years of wood use (no.)0-15 17% (15/88) 59% (38/64)

16-30 36% (32/88) 25% (16/64)30+ 46% (41/88) 15% (10/64)

Wood as cooking fuel Case Control OR (95% CI)Yes 75 40 2.50 (1.14, 5.49)No 13 24

Years of wood use0-15 15 38 Ref

16-30 32 16 5.07 (2.01, 12.94)30+ 41 10 10.4 (3.83, 28.95)

Cigarette Smokers Case Control% Reporting tobacco use (no.)

41% (63) 24% (25)

Pack years0-19 49% (21/43) 76% (19/25)

20-39 37% (16/43) 24% (6/25)40+ 14% (6/43) 0% (0/25)

Cigarette Smokers Case Control OR (95% CI)Yes 26 6 3.05 (0.96, 10.71)No 27 19

Pack years0-19 21 19 Ref

20-39 16 6 2.41 (0.70, 9.03)40+ 6 0 Undefined (1.30, UHigh)

Variable Adjusted OR 95% CI

Wood use 3.92 ( 1.7-9.1 )Tobacco use 2.64 ( 1.2-5.5 )Husband smokes 2.04 ( 1.1, 3.9 )Gasoline use 0.53 ( 0.27, 1.03)

Table 3. Odds ratios and confidence intervals for the same variables shown in Table 1, only now adjusted for each other and age and hospital

Variable Unadjusted OR 95% CIWood use 3.44 ( 1.70, 7.14 )Tobacco use 2.23 ( 1.18, 4.04 )Husband smokes 2.06 ( 1.08, 3.93 )Gasoline use 0.52 ( 0.29, 0.96)

Table 1. Summary of unadjusted odds ratios and confidence intervals

Question 9. Interpret the results in Table 3, Do they differ from the results in Table 1? Why or Why not?

Question 10. Calculate the etiologic fraction of COPD in this population attributable to using wood as a cooking fuel. Interpret its meaning.

Where = proportion of exposed in the controls

Etiologic Fraction or Attributable Fraction

We would expect a 64% reduction in COPD in this population if we were able to eliminate using wood as a cooking fuel.