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Prevalence of residents with chronic obstructive pulmonary disease and risk factor analysis in Dongguan Shi long region in Guangdong Province

Lei Wu1, Meihua Chen1*, Taorong Xu2 and Yanling Cai1

1Department of Respiration Medicine, the Third People’s Hospital of Dongguan, Dongguan, Guangdong, PR China

2Department of Nephrology and Gastroenterology, the Third People’s Hospital of Dongguan, Dongguan, Guangdong, PR China

*Corresponding Author:
Meihua Chen
Department of Respiration Medicine
The Third People’s Hospital of Dongguan, PR China

Accepted date: May 12, 2017

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Abstract

Purpose: To investigate the prevalence of residents with Chronic Obstructive Pulmonary Disease (COPD) and related risk factors in the Dongguan Shi long region of Guangdong Province, China.

Method: Random samples of patients more than 40 y of age with high-risk COPD from the region underwent pulmonary function testing and completed a questionnaire survey to determine the prevalence of COPD. Then, single and multiple factor logistic analysis was carried out on the influencing factors.

Results: The overall COPD prevalence in this region was 9.05%; the prevalence for males was higher than females. With aging, the prevalence of COPD increased significantly (P<0.05). COPD was mainly grades I and II. The differences between COPD patients and non-COPD patients pertaining to gender, age, education level, Body Mass Index (BMI), a family history of respiratory disease, and Smoking Index (SI) were significant (P<0.05). Logistic multi-factor regression analysis showed that BMI, age, gender, and SI were risk factors for COPD prevalence (P<0.05 or P≈0.05).

Conclusion: The prevalence of COPD in this region was higher, and BMI (higher), age (elder), gender (male), and SI (higher) were shown to be risk factors. Therefore, active intervention for these risk factors should be offered to reduce the COPD prevalence in this region.

Keywords

Single factor, Chronic obstructive pulmonary disease (COPD), Smoking index, Prevalence.

Introduction

The Global Burden of Disease Study projected that Chronic Obstructive Pulmonary Disease (COPD) ranked sixth as a cause of death in 1990 [1]. Based on the relevant data, COPD mortality was ranked fourth in the world in 2010, behind cancer, cardiovascular and cerebrovascular diseases [2,3], and will become the third leading cause of death worldwide by 2020 [4]. Data involving the urban population of China indicated that respiratory diseases (mostly COPD) accounted for 13.89% of deaths, and was thus fourth among causes of death. Among the causes of death in rural areas, respiratory diseases accounted for 22.4%, ranking first. Indeed, the number of patients in China who die of COPD disease is approximately 1 million each year [5,6]. Although previous studies have advanced a clear theory on the pathogenesis and pathophysiologic process of COPD [7-9], the impact of an aging population, environmental pollution, and increase in smokers on the increased mortality rate suggests that more effort on clinical prevention is needed. Furthermore, research has demonstrated that COPD is associated with heredity and the environment, and the pathogenesis has shown that COPD is preventable [10,11]. Therefore, identifying the pathogenic characteristics and risk factors for COPD in an effort to provide guidance for early screening and intervention in highrisk groups to delay the progression of COPD is of primary importance. This study focused on the morbidity of COPD in the Dongguan Shi long region of Guangdong Province, China, and investigated the distribution of high-risk groups and main risk factors by collecting demographic characteristics and using statistical methods. The COPD patients included in this study were collected from December 2011 to December 2012 in this region.

Materials and Methods

Clinical materials

Random samples of COPD high-risk patients>40 y of age from the residents in Dongguan Shi long region, Guangdong Province between December 2011 and December 2012. Patients who did not undergo pulmonary function testing, had a severe mental illness or cardiovascular disease, underwent major chest surgery history within 2 months, or had lifethreatening disease were excluded from the analysis. A total of 2267 questionnaires were distributed, 2243 of which were valid for an effective response rate of 98.94%. The respondents were 41-77 y of age, with an average age of 55.8 ± 8.6 y.

Questionnaire survey

A questionnaire was self-designed by our hospital (The prevalence of community COPD high-risk population and its related risk factors) and included the following: (1) gender, age, education level, occupation, and other demographic characteristics; and (2) diseases and exposure history, including personal and family histories, smoking history, living habits, economic status, respiratory symptoms, Body Mass Index (BMI), and inducing factors. Subjects received the necessary physical examinations, and the questionnaires were surveyed under the guidance of professional training community medical workers. Moreover, the investigation standard was uniform to ensure the reliability and validity of the questionnaire, and the entire investigation process was monitored by the person in charge.

Lung function testing

A QUARK PFT4 lung function detector (COSMED, Rome, Italy) was utilized to test lung function by measuring lung volume, flow rate, breathing time, and intra-pulmonary pressure. In the process of testing, subjects were instructed to continue breathing through their mouths when breathing in, ensure there is no leaking, and then breathe out into the instrument as fast as possible. The following critical indicators were recorded: Forced Vital Capacity (FVC); the percentage of forced vital capacity accounted for the predicted value (FVC %); forced expiratory volume in 1 s (FVC1); and the ratio of FEV1-to-FVC (FVC1%). All subjects were required to complete two tests and keep the error within 5% if possible. The best results were used for analysis.

Assessment of the COPD high-risk population

Patients were>40 y of age and met any one of the following criteria: (1) long-term cough and expectoration that conformed to the clinical diagnostic standards of chronic bronchitis; (2) in a smoking environment long-term, or chronic exposure to particles, dust, or harmful gas; and (3) breathing after exercise or activity was lower than the same age group [12].

Criteria for COPD

Based on the COPD global prevention and control initiative and the standards established by the Chinese Respiratory Society [13,14], the diagnosis of COPD was established as follows: 15-30 min after pre-treatment with a 200 μg dose bronchodilator, a FEV1/FVC ≤ 0.7 confirmed the presence of airflow limitation that is not fully reversible; relevant risk factors; and excluding other systemic diseases.

Statistical methods

SPSS17.0 statistical software was used for data analysis. Observation data were mainly counted data. A χ2 test or rank sum test was utilized for single factor analysis (comparison between groups). Logistic multi-factor regression analysis was further applied for the factors, the differences of which were more apparent in single factor analysis. In addition, the Cochran Armitage trend test was used for some indicators among age levels. Significant associations were defined as P<0.05.

Results

Overview of survey samples

In the current study, the valid investigation involved 2243 people and the number of patients was 203. The total incidence of COPD was 9.05%. The prevalence of COPD for males (14.33%) was higher than females (4.98%; Table 1). Furthermore, Table 2 shows that the majority of COPD cases were grades I and II. With aging, the incidence of COPD increased significantly.

Age group Male Female Total
Sample size Cases OR (95% CI) P Sample size Cases OR (95% CI) P Sample size Cases OR (95% CI) P
40-49 334 20 (5.99%) 1   463 6 (1.30%) 1   797 26 (3.26%) 1  
50-59 252 26 (10.32%) 1.72 (0.94-3.16) 0.053 331 10 (3.02%) 2.33 (0.84-6.48) 0.08 583 36 (6.17%) 1.89 (1.13-3.17) 0.01
60-69 256 50 (19.53%) 3.26 (1.89-5.62) <0.001 331 30 (9.06%) 6.99 (2.88-16.99) <0.001 587 80 (13.63%) 4.18 (2.65-6.59) <0.001
>70 135 44 (32.59%) 5.44 (3.09-9.58) <0.001 141 17 (12.06%) 9.30 (3.60-24.05) <0.001 276 61 (22.10%) 7.00 (4.34-11.31) <0.001
Total 977 140 (14.33%) 2.39 (1.47-3.89) <0.001 1266 63 (4.98%) 3.84 (1.65-8.93) <0.001 2243 203 (9.05%) 2.77 (1.83-4.21) <0.001
Cochran armitage P <0.001       <0.001       <0.001      

Table 1: The prevalence of COPD in different gender and age.

Age group Level I Level II Level III Level IV Total
40-49 17 (65.4%) 9 (34.6%) 0 (0%) 0 (0%) 26 (100%)
50-59 19 (52.8%) 10 (27.8%) 7 (19.4%) 0 (0%) 36 (100%)
60-69 40 (50.0%) 36 (45.0%) 2 (2.5%) 2 (2.5%) 80 (100%)
>70 35 (57.4%) 16 (26.2%) 10 (16.4%) 0 (0%) 61 (100%)
Total 111 (54.7%) 71 (35.0%) 19 (9.3%) 2 (1.0%) 203 (100%)
Cochran armitage P 0.608        

Table 2: Severity of COPD in different ages.

Single factor analysis correlated with COPD

All of the risk factors in the investigation data that might influence the development of COPD, such as age, gender, and 10 other variables, were used for the single factor analysis. The results suggested that there were significant differences in gender, age, education level, BMI, family history of respiration, smoking index (SI, an indicator of smoking exposure level by smoking history and daily smoking), and others between the COPD and non-COPD patients (P<0.05) are shown in Table 3.

Risk factors COPD (No=203) Non-COPD (No=2040) χ2 P
Age 40~50 26 (12.8%) 855 (41.9%) 154.397 <0.001
51~60 36 (17.7%) 624 (30.6%)
61~70 80 (39.4%) 307 (15.0%)
>70 61 (30.0%) 254 (12.5%)
Gender Male 140 (69.0%) 977 (43.6%) 48.433 <0.001
Female 63 (31.0%) 1266 (56.4%)
SI (per year)c <300 96 (47.3%) 1634 (80.1%) 158.169 <0.001
301~600 34 (16.7%) 234 (11.5%)
<600 73 (36%) 172 (8.4%)
Family history of respiratory disease Yes 171 (84.2%) 978 (47.9%) 97.346 <0.001
None 32 (15.8%) 1062 (52.1%)
Average monthly household income (Yuan) <1000 73 (36.0%) 824 (40.4%) 3.853 0.146
1001~3000 74 (36.5%) 855 (41.9%)
>3000 46 (22.7%) 371 (18.2%)
Education level Primary school and below 107 (52.7%) 473 (23.2%) 85.179 <0.001
Middle school 52 (25.6%) 959 (47.0%)
High school and above 44 (21.7%) 608 (29.8%)
Dust exposure history Yes 103 (50.7%) 960 (47.1%) 1.003 0.317
None 100 (49.3%) 1080 (52.9%)
BMI (kg/m2)b <18.5 64 (31.5%) 416 (20.4%) 26.693 <0.001
18.6~25 95 (46.8%) 834 (40.9%)
>25 44 (21.7%) 790 (38.7%)
History of childhood respiratory tract diseases Yes 90 (44.3%) 1030 (50.5%) 2.798 0.094
None 113 (55.7%) 1010 (49.5%)

Table 3: Distribution of demographic characteristics.

Logistic multi-factor regression analysis

The factors that were significantly different in single factor analysis, such as age, gender, and five other factors, were chosen for multi-factor comprehensive analysis and logistic regression. For the response variable, we assigned COPD a 1 and non-COPD a 0. The results showed that age, gender, and BMI were positively correlated with COPD (P<0.05; relative risk>1). In addition, SI was also an important factor that should not be dismissed. Moreover, BMI had the highest relative risk (1.983) among the exposure factors, which indicated that BMI was the most critical risk factor for COPD in our study. Furthermore, the analysis of other factors, including education level and family history of respiratory disease, are shown in Table 4.

Factors Assignment description Coefficient Standard error Wald chi square OR (95% CI) P value
Age 40~50       1 (Reference)  
51~60 0.055 0.046 1.4 1.39 (0.81-2.38) 0.148
61~70 0.208 0.04 22.06 3.08 (1.90-4.99) <0.001
≥ 70 0.152 0.042 11.654 2.35 (1.43-3.86) <0.001
Gender Female       1 (Reference)  
Male 0.177 0.039 19.788 2.22 (1.56-3.17) <0.001
BMI (kg/m2)b ≤ 18.5       1 (Reference)  
18.6~25 0.087 0.042 4.356 1.48 (1.02-2.15) 0.023
≥ 25 -0.075 0.044 2.93 0.69 (0.45-1.06) 0.054
SI (per year)c ≤ 300       1 (Reference)  
301~600 -0.202 0.04 22.701 0.35 (0.23-0.55) <0.001
≥ 600 -0.062 0.041 2.214 0.76 (0.53-1.09) 0.081
Education level Primary school and below       1 (Reference)  
Middle School -0.154 0.041 13.802 0.49 (0.33-0.71) <0.001
High school and above -0.183 0.04 19.407 0.41 (0.28-0.61) <0.001
Family history of respiratory disease None     1 (Reference)    
Yes -0.053 0.04 1.74 0.80 (0.57-1.12) 0.109

Table 4: Results of multivariate logistic regression.

Further analysis of age trends

Based on the multi-variate analysis, we found that age and other factors were important influencing factors for COPD. In contrast, taking into account that the subjects aged from 40-70 y and the uneven distribution of morbidities, we explored the relationship between COPD prevalence and the different age groups by stratified analysis and the Cochran Armitage trend test to identify the underlying incidence characteristics. Table 1 shows the incidence analysis of patients as a function of aging and gender. The results demonstrated that the Cochran Armitage χ2 test (P<0.01) was independent of gender, which indicated that with aging, the prevalence of COPD increased. Table 2 shows the trend analysis with changes in the age of patients with different severity of disease. The Cochran Armitage χ2 test (P>0.05) illustrated that with changes in age, the distribution of COPD disease severity was not apparent. Based on the data, all age groups were mainly grades I and II, and most were grade I, which is in support of the abovementioned results.

Discussion

COPD is a common and frequently occurring disease in the clinic setting. The incidence of COPD varies greatly as a function of different geographic regions, age groups, research populations, and research methods [15]. In recent years, there have been many reports on COPD epidemiologic surveys. Although the results are not the same, the general trend and the epidemiologic characteristics are consistent, which could be reference each other. Data from most nations have shown that the prevalence of COPD is <6% in the adult population [16]. In all Latin American cities, the prevalence of COPD is appreciably higher in males than females [17]. In China, a large, population-based survey in seven provinces/cities, including Northern, Eastern, Southern and Western areas, has shown the overall prevalence of COPD to be 8.2% (12.4% in males and 5.1% in females)>40 y of age [18]. The prevalence of COPD is significant higher in smokers and ex-smokers than non-smokers [19]. In the current study, the total prevalence of COPD was 9.05% in Dongguan Shi long region of Guangdong Province, was slightly higher than 8.2%, the COPD prevalence in China reported in a large-scale survey [18] and much higher than 5.9%, the prevalence of COPD from an earlier survey in Nanjing Municipality, the capital city of Jiangsu province [20]. In comparison with other studies in similar age groups, the prevalence of COPD in the Dongguan Shi long population was slightly lower than Japan (10.9%) [19], Warsaw, Poland (10.7%) [21], and much lower than Salzburg, Austria (26.1%) [22]. Consequently, these reports had some differences compared to our research, which might reflect the different countries, regions, customs, climate, and environment, as well as the different investigation methods. It has been reported [23,24] that the clinical symptoms of COPD are not evident with the inducement of cold, cold air, and smoking. Thus, asymptomatic patients with COPD should be the focus of attention in the clinical differential diagnosis to eliminate the symptom inducement and reduce the rate of clinical misdiagnosis and missed diagnosis.

Smoking is one of the recognized risk factors for the cause of COPD worldwide. Moreover, global research [25-27] has shown that smoking can increase the clinical prevalence of COPD, and can impair the immune system in a variety of ways. In the current research, the results demonstrated that the prevalence of COPD was significantly increased when SI was >300. Cigarettes contain nicotine, tobacco tar, carbon monoxide, nitrous amines, and other harmful substances, and when inhaled, the substances may activate alveolar macrophages, T lymphocytes, and neutrophils to release a variety of media. Subsequently, the lung structure is damaged and exhibits an airway inflammatory reaction. In contrast, the secretion of airway mucus and airflow obstruction increase, which is a major cause of COPD [28,29]. A predictive study [30] suggested that patients with persistent smoking enhance the clinical mortality of COPD. Therefore, it is of great significance for the improvement of COPD disease progression and number of deaths to cease smoking as soon as possible.

Older age and male gender are predisposing factors for COPD. The current research showed that the occurrence of COPD is positively correlated with the age of the patient. Moreover, the prevalence of COPD in males was higher than females in the Dongguan Shilong region of Guangdong province, and with aging, the prevalence of COPD increased significantly, which is consistent with previous reports [31,32]. In addition, age and gender may be associated with persistent inflammation in the lung, sustained bronchodilation, and continuous reduction of lung volume by the intake of harmful substances through daily smoking. The change in the aging population structure in China is also one of the reasons leading to the rise in COPD clinical prevalence.

There are some potential limitations to this study. The main limitation of our study was the small number of COPD cases. Therefore, a further study with a larger number of patients is required. Another limitation was that the duration of smoking was not factored into the analysis. A further limitation was that all information on the questionnaire survey pertaining to diseases and exposure history was self-reported and subject to recall bias and misclassification.

The current research suggested that BMI is an independent influencing factor for COPD. While the prevalence of COPD was higher for patients with a low BMI, immune resistance in patients with a low BMI is poor, and poor nutritional status exists. Moreover, COPD also decreases exercise tolerance and patient weight, thus creating a vicious circle. Of note, this research did not obtain the family history, and education level presented a significant correlation with COPD, which still needs further investigation.

Conclusion

In general, this study showed that smoking will greatly increase the incidence of COPD when the SI is >300 and the morbidity of COPD were positively correlated with the age of patients, especially in elderly males. Moreover, BMI is another independent exposure factor for COPD, which has a positive correlation with the prevalence of COPD. Therefore, this study provided more evidence for COPD risk factors and we should focus on the above-mentioned points for the primary prevention and treatment of COPD.

Acknowledgements

This project was supported by the Science and Technological Program for Dongguan’s Higher Education, Science and Research, and Health Care Institutions (No. 20101051502401).

Disclosure of Conflict of Interest

None

References