(Chest. 2005;128:2818-2823.)
© 2005
American College of Chest Physicians
Prevalence of Physician-Diagnosed COPD and Its Association With Smoking Among Urban and Rural Residents in Regional Mainland China*
Fei Xu, BMed, BEcon;
XiaoMei Yin, BMed;
Min Zhang, BMed;
HongBing Shen, MD, PhD;
LinGeng Lu, PhD and
YaoChu Xu, BMed
* From Nanjing Municipal Center for Disease Control and Prevention (Drs. Yin and Zhang), Nanjing, China; the School of Public Health (Drs. Shen and F. Xu), Nanjing Medical University, Nanjing, China; Department of Epidemiology and Public Health (Dr. Lu), Yale University School of Medicine, New Haven, CT; and NanJing Medical University (Dr. Y. Xu), Nanjing, China.
Correspondence to: Fei Xu, BMed, Nanjing Municipal Center for Disease Control and Prevention, 2 ZiZhuLin, Nanjing, ROC 210003; e-mail: f_xufei{at}hotmail.com
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Abstract
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Objectives: To investigate the prevalence of physician-diagnosed COPD and to explore the relationship between the total amount of cigarettes smoked (TACS) and COPD among urban and rural adults in Nanjing, China.
Design: Population-based, cross-sectional study conducted between October 2000 and March 2001.
Setting: Administrative villages (n = 45) randomly selected from three urban districts and two rural counties of Nanjing municipality, Jiangsu province, China, with an overall population of 5.6 million.
Participants: All regular local residents 
35 years old (n = 29,319), 67.7% from urban areas and 32.3% from rural areas; 49.7% were men and 50.3% were women.
Results: The response rate of potential participants was 90.1%. The overall prevalence of diagnosed COPD was 5.9%. The prevalence of COPD was significantly higher among men than in women (7.2% vs 4.7%, p = 0.000), while the difference between urban and rural participants was not statistically significant (6.7% vs 4.4%, respectively; p = 0.132). The prevalence of COPD was significantly higher among smokers than nonsmokers. After adjusting for age, gender, area of residence, fuels, heating in winter, ventilation in kitchen, passive smoking, education, occupation, average family income, alcohol drinking, cooking oil, body mass index, and physical activity, a dose-response relationship between COPD and TACS was evident in this population (odds ratio [OR], 1.60; 95% confidence interval [CI], 1.34 to 1. 92; OR, 1.39; 95% CI, 1.13 to 1.70; and OR, 1.24; 95% CI, 1.01 to 1.52 for smokers within upper, middle, and lower TACS levels compared with nonsmokers, respectively).
Conclusions: The overall prevalence of diagnosed COPD (5.9%) among Chinese adults was higher than that (2.5%) estimated by World Health Organization experts, and there was a significant gradient increase in COPD prevalence from the stratum of nonsmokers to the stratum of upper TACS.
Key Words: China • cigarette smoking • COPD • prevalence • total amount of cigarettes smoked
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Introduction
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COPD is one of the most common public health problems worldwide and is the fourth-leading cause of death in the world.12 It has been estimated that COPD will become the third-most-frequent cause of death and the fifth-most-common cause of disability by the year 2020.3 According to a comprehensive review,4 the overall prevalence of COPD ranges from < 1 to > 18% in different populations, and this variation is probably due to different methods used in the estimations. In mainland China, COPD is currently the second-leading cause of death.5 However, the only COPD prevalence available for mainland China is 2.5% overall, which was estimated based on World Health Organization (WHO) expert opinions.4 Instead of conducting population surveys, the WHO experts estimated the prevalence of COPD on the basis of published and unpublished studies. If the data were not available, experts would often make "informed estimates" based on the prevalence in similar countries or regions.
The prevalence of cigarette smoking among adult men was 63.0% in mainland China, which is the greatest producer and consumer of cigarettes in the world.67 If the assumption is made that approximately 10 to 15% of smokers will acquire COPD,89 the prevalence of COPD in mainland China should be between 6.3% and 9.5%, which is much higher than the WHO-estimated percentage of 2.5%. The purposes of this study were to estimate the prevalence of diagnosed COPD in China based on the data collected in both urban and rural areas of Nanjing municipality between October 2000 and March 2001, and to examine the association of COPD with smoking. An objective estimation of COPD prevalence and a better understanding of its association with smoking in the context of China would be helpful for people in their fight against COPD in developing countries.
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Materials and Methods
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Sample Selection
A large-scale, population-based, cross-sectional study was conducted in Nanjing municipality, which is the capital of Jiangsu province, and is located in eastern China, with a population of approximately 5.6 million. In mainland China, the administrative system consists of five strata: central government, provincial/municipal government, district/county government, street/town government, and administrative village. Nanjing municipality has 15 administrative units: 10 urban districts and 5 rural counties. The administrative village-based samples were selected using a multistage sampling method. As shown in Figure 1
, we first randomly selected three urban districts and two rural counties; then three streets/towns from each chosen district/county; and finally three administrative villages in each street/town. This resulted in a total of 45 villages. All participants aged 35 years old and who had been local residents for at least 5 years were included in this study.
Questionnaire and Definitions
After informed consent was obtained, each subject was administered a household interview by trained health-care professionals. The questionnaire included general information such as age, gender, education level, occupation, number of family members, total monthly family income, body weight and height, and specific questions, eg, physical activity, use of cooking oil, alcohol drinking, smoking, exhaust fans used in the kitchen, and heating method in winter (electricity/gas, firewood/straw, coal/oil).
The diagnosed COPD cases were defined as persons with chronic bronchitis and/or emphysema based on physician diagnosis. Chronic bronchitis refers to a productive cough for at least 3 months of each of 2 successive years for which other causes were ruled out. Emphysema describes the destruction of the lung architecture with enlargement of the airspaces and loss of alveolar surface area. The study participants reported their COPD status according to the question, "Have you ever been diagnosed with chronic bronchitis and/or emphysema by a doctor or doctors at a grade 1 or higher hospital?" If the answer was "yes," the participants were asked to show their medical records for confirmation. In mainland China, hospitals are classified by grade, from higher to lower: grade 3, grade 2, grade 1, and general practitioner clinics. All outpatients usually keep their personal medical records, which include the dates of visiting doctors, diagnosed diseases, prescriptions, and treatment recommendations. However, we could not get the information on the evidence of diagnostic documents because original reports of medical tests (including spirometry) were not included in personal medical records.
Smoking status categories were defined as follows: (1) current smoker, who smoked at least one cigarette per day continuously for at least 1 year, or smoked at least 18 packs in total each year; (2) ex-smoker, who previously smoked but subsequently quit smoking for > 1 year; and (3) nonsmoker, who did not meet the criteria for either current smokers or ex-smokers, including those who smoked in the past year but < 18 packs.10 Both current smokers and ex-smokers were categorized as smokers in this study. The total amount of cigarettes smoked (TACS) was calculated based on the multiplication of the number of cigarettes smoked per day by number of smoking days, after which the variables of total amount of cigarettes smoked was categorized by tertiles: lower, middle, and upper. Therefore, participants were categorized into one of four smoking status groups: nonsmokers as the reference, and smokers with lower, middle, and upper TACS, respectively. Participants were also classified into three age groups: younger (35 to 49 years), middle (50 to 64 years), and older ( 65 years). Occupation status was grouped into job 1 (farmer, factory worker, forestry worker, fisherman, military person), job 2 (salesperson, house worker, vehicle driver), and job 3 (office worker, teacher, doctor, retired, academic researcher, government officer).
Participants were also categorized into different groups by several other variables. Education levels were 0 to 9 years, 10 to 12 years, and 13 years. Occupational physical activities included "light" (receptionist, office worker, assembly worker), "moderate" (repairer, electrician, machinist), and "vigorous" (farmer, steel maker, lumberman); leisure-time physical activities included light (cooking, flower growing, watching television), moderate (jogging, dancing, Chinese TaiJi), and vigorous (ball playing, field running). Drinkers were defined as subjects who drank alcohol at least twice per week on average for at least 1 year. Ex-drinkers were those who previously drank but had not drank for at least 1 year. Nondrinkers were those who never drank or drank occasionally in the past year but less than twice per week.
A family was defined as a group who lived together and shared living-related expenses. The total monthly income of all family members was the monthly total earnings of the whole family. This included salaries, pensions and allowances, money from selling goods and products, and the estimated market price value of products for personal/family consumption. Family average income, the average total monthly income of all family members, was divided into tertiles: low, middle, and high.
Participants, wearing light indoor clothing and without shoes, had their weight measured to the nearest 100 g using a beam balance scale, and had their height measured to the nearest millimeter using a stadiometer. Weight and height were measured twice, and the mean values of the reading were used for the analysis. Body mass index (BMI) was calculated by dividing weight by the square of height. Participants with BMI 24 kg/m2 were categorized as overweight (BMI, 24 to 28 kg/m2) or obese (BMI > 28 kg/m2).1112
Data Management and Analysis
Data were double-entered and cleaned (Epi Info, Version 6.04; Centers for Disease Control and Prevention; Atlanta, GA) and were managed and analyzed (SPSS, Version 10.0; SPSS; Chicago, IL). The association between TACS categories and potential confounders was investigated using the 
2 test. We calculated odds ratios (ORs) together with 95% confidence intervals (CIs), both univariately and multivariately, using logistic regression analysis. Potential confounders were adjusted for by the multivariate logistic regression model in our analysis.
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Results
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There were a total of 29,319 survey respondents from 15,300 households. The response rate among adults in the selected villages was 90.1%. There were no significant differences in terms of demographic variables between respondents and those who did not take part in this survey. The final sample was representative of the municipality by age, gender, and residential area. Urban and rural residents consisted of 67.7% and 32.3%, respectively. Moreover, 49.7% were men and 50.3% were women. The demographic characteristics of the participants are shown in Tables 1 and 2
. The average pack-years of cigarettes smoked was 7,688 for urban smokers and 9,671 for rural smokers. Male smokers consumed 8,477 cigarettes on average, while female smokers consumed 7,045 cigarettes on average.
Table 3
presents the overall prevalence of known COPD and its association with TACS levels. The overall prevalence of diagnosed COPD was 5.9%, and it was significantly higher among smokers (7.30%) than nonsmokers (5.36%). A gradient increase in adjusted OR was found from participants with lower TACS levels to upper TACS levels (OR, 1.63; 95% CI, 1.37 to 1.95; OR, 1.40; 95% CI, 1.15 to 1.72; and OR, 1.25; 95% CI, 1.02 to 1.35 for smokers with upper, middle, and lower TACS levels relative to nonsmokers, respectively). Moreover, a dose-response association between COPD and TACS was still evident after adjusting for age, gender, area of residence, fuels, heating in winter, kitchen ventilation, passive smoking status, education level, occupation, family average income, drinking, cooking oil, BMI, and physical activity.
Table 4
shows the prevalence of diagnosed COPD by age, gender, and residential area within different TACS strata. The prevalence in men (7.2%) was significantly higher than in women (4.7%). For urban and rural participants, no statistical difference was detected between the overall and TACS-stratified COPD prevalence. There was a gradient increase in COPD prevalence from younger to elder subjects, whether they were smokers or not.
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Table 4.. Prevalence of COPD and Its Association With Age, Gender, and Living Area Stratified by TACS in Nanjing, China
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Table 5
presents the gender-specific prevalence of diagnosed COPD by TACS categories, urban and rural area, and age. Compared with women, men were more likely to have COPD among nonsmokers and lower TACS group. A dose-response relationship between COPD prevalence and TACS was also found in women; however, only men with upper TACS had a significantly higher prevalence of COPD relative to nonsmokers in this population.
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Table 5.. Prevalence of COPD and Its Association With TACS, Living Area, and Age Stratified by Gender in Regional China
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Discussion
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The focus of this study was to estimate COPD prevalence and to examine its associations with smoking in a Chinese population. To the best of our knowledge, this is the first systematic population survey (n = 29,319) on COPD prevalence based on patients reported in mainland China. This study presents a diagnosed COPD prevalence (5.9%) among urban and rural populations 35 years old, which is higher than that (2.5%) estimated by WHO experts4 and what was reported (3.5%) in Hong Kong, China.13
After adjusting for possible confounding variables, smoking was positively associated with COPD prevalence in both men and women in this Chinese population. Men had higher COPD prevalence than women. The relationship between prevalence of COPD and TACS was dose dependent by gradient in women, while men with only upper TACS were more likely to have COPD. These findings indicate that cigarette smoking is more harmful to women than men regarding COPD. However, there was no statistical association of COPD with fuels, heating in winter, kitchen ventilation, cooking oil, and passive smoking in this study population. This is inconsistent with other reports131415 that indoor air pollution from combustion of biomass/traditional fuels and coal is a risk factor of COPD. In China, biomass/traditional fuels (coal, oil, firewood, and straw) are widely used in rural areas. In this study, 92.0% (8,717 of 9,470 participants) from rural areas used biomass/traditional fuels. In fact, the kitchens were usually larger in the rural areas than the urban areas, and the kitchen doors and windows were usually opened at the time of cooking. In urban areas, 79.9% (15,868 of 19849 participants) used exhaust fans in kitchens when cooking. Thus, the kitchen air of participants in this study might not be severely polluted, and this may be an explanation for the inconsistency.
The smoking rate was 58.6% for men and 2.2% for women. The prevalence of COPD in women (4.7%) was higher than the overall estimate (2.5%) by WHO experts but was significantly lower than that in men (7.2%), which was consistent with other reports.1617 Similar to a report from Canada,18 the COPD prevalence in female smokers was higher than that in male smokers (15.74% vs 6.98%; OR, 2.50; 95% CI, 1.83 to 3.40), indicating that female smokers are more susceptible to COPD compared to male smokers in this Chinese population. Generally, women do more housework (such as housekeeping and cooking) in China but, after adjustment for potential confounding factors, fuels and cooking oil were not associated with COPD in this population. There was no convincing evidence from this study to explain why female smokers are more likely to acquire COPD compared to male smokers. Further studies are warranted to explore whether gender is an independent risk factor of COPD.
This study has two primary limitations. First, the diagnostic methods, especially spirometry, were not examined, thus leading to potential misclassification of COPD. Second, it is possible that bias could have resulted from different patients receiving a diagnosis of COPD by different physicians in different hospitals at different times.
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Conclusions
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The overall prevalence of diagnosed COPD (5.9%) among Chinese adults was higher than that (2.5%) estimated by WHO experts, and COPD was positively associated with smoking in this Chinese population. There was a significant gradient increase in COPD prevalence from the stratum of nonsmokers to the stratum of upper TACS in this study, and female smokers were more likely to acquire COPD compared to male smokers. Fuels, heating in winter, ventilation in kitchens, and use of cooking oil were not significantly associated with COPD.
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Acknowledgements
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We thank Professor Zuo-Feng Zhang, School of Public Health, UCLA, for his kind help in editing the manuscript, and Nanjing Municipal Department of Health for its generous financial support of this study. Our special thanks go to the following for their support of the study: Departments of Health of XuanWu District, JianYe District, DaChang District, JiangPu County and GaoChun County, the Centers for Disease Control and Prevention of JiangSu Province, XuanWu District, JianYe District, DaChang District, JiangPu County and GaoChun County, and the interviewers and investigators who participated.
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Footnotes
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Abbreviations: BMI = body mass index; CI = confidence interval; OR = odds ratio; TACS = total amount of cigarettes smoked; WHO = World Health Organization
Received for publication January 6, 2005.
Accepted for publication April 28, 2005.
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Abstract
Introduction
