|Year : 2020 | Volume
| Issue : 1 | Page : 78
Burden of obstructive lung disease in Iran: Prevalence and risk factors for COPD in North of Iran
Hooman Sharifi1, Mostafa Ghanei2, Hamidreza Jamaati3, Mohammad Reza Masjedi4, Mohsen Aarabi5, Ali Sharifpour6, Golnar Radmand3, Hadis Najafimehr7, A Sonia Buist8
1 Tobacco Prevention and Control Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran
2 Chemical Injuries Research Center, Systems Biology and Poisonings Institute, Baqiyatallah University of Medical Sciences, Tehran, Iran
3 Chronic Respiratory Diseases Research Center, National Research Institute of Tuberculosis and Lung Diseases (NRITLD), Shahid Beheshti University of Medical Sciences, Tehran, Iran
4 Tobacco Control Research Center, Iranian Anti Tobacco Association, Tehran, Iran
5 Diabetes Research Center, Mazandaran University of Medical Sciences, Sari, Iran
6 Department of Internal Medicine, Pulmonary and Critical Care Division, Mazandaran University of Medical Sciences, Sari, Iran
7 Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran
8 Division of Pulmonary and Critical Care Medicine, Oregon Health and Science University, Portland, Oregon
|Date of Submission||16-Oct-2018|
|Date of Acceptance||16-Aug-2019|
|Date of Web Publication||03-Jul-2020|
Chemical Injuries Research Center, Systems Biology and Poisonings Institute, Baqiyatallah University of Medical Sciences, Tehran
Source of Support: None, Conflict of Interest: None
Background: Globally chronic obstructive pulmonary disease (COPD) was reported as the fourth leading cause of death (5.1%) in 2004 and is projected to occupy the third position (8.6%) in 2030. The goal of the present project is to describe the prevalence and risk factors of COPD in a province in the north of Iran. Methods: This study followed a stratified cluster sampling strategy with proportional allocation within strata. The stratification of the sample according to the 31 provinces of Iran is incorporated in the sampling process. The single most important outcome measure obtained as part of this protocol was spirometry before and after the administration of 200 mg (2 puffs) of salbutamol. The descriptive statistics for categorical variables included the number and percent and for continues variables included the mean ± SD. Results: A total of 1007 subjects were included in the study. Among all participants, 46 (5%) subjects had COPD on the basis of symptoms and 43 (8.3%) subjects had COPD on the basis of spirometry criteria. In univariate analysis, urban inhabitants in comparison with rural inhabitants had lower COPD risk (OR: 0.48; 95% CI: 0.24–0.95), smoker had higher risk compared with nonsmokers (OR: 1.97; 95% CI: 1.01–3.82), and subjects with exposure to dust (OR: 2.07; 95% CI: 1.09–3.94) had higher risk compared with contrary status. Conclusions: This study showed that occupational and environmental smoke exposure was associated with COPD. A new design of preventive measures must be taken to control cooking energy and cooking stoves, particularly in rural areas.
Keywords: Airway obstruction, burden of obstructive lung disease, Iran, prevalence
|How to cite this article:|
Sharifi H, Ghanei M, Jamaati H, Masjedi MR, Aarabi M, Sharifpour A, Radmand G, Najafimehr H, Buist A S. Burden of obstructive lung disease in Iran: Prevalence and risk factors for COPD in North of Iran. Int J Prev Med 2020;11:78
|How to cite this URL:|
Sharifi H, Ghanei M, Jamaati H, Masjedi MR, Aarabi M, Sharifpour A, Radmand G, Najafimehr H, Buist A S. Burden of obstructive lung disease in Iran: Prevalence and risk factors for COPD in North of Iran. Int J Prev Med [serial online] 2020 [cited 2021 Nov 29];11:78. Available from: https://www.ijpvmjournal.net/text.asp?2020/11/1/78/288969
| Introduction|| |
Chronic obstructive pulmonary disease (COPD) is a chronic respiratory disease with an increasing prevalence worldwide, especially in developing countries. COPD is a global health burden that affects 300 million people worldwide resulting in >3 million deaths annually., Globally COPD was reported as the fourth leading cause of death (5.1%) in 2004 and is projected to occupy the third position (8.6%) in 2030. A majority of COPD-related deaths occurs in low- and middle-income countries. In 2010, it was said that above 230 million people living in urban areas (prevalence of 13.6%), and >3.7 million people living in rural areas (prevalence of 9.7%), were affected by COPD. In published studies, the prevalence of COPD has been reported as a considerable range of estimates across different countries. This rate was reported between 0.2% in Japan and 37% in the USA. It is said that merely around one-fourth of cases are diagnosed at the early stages. COPD is characterized by chronic inflammation and non-fully reversible airflow obstruction, involving structural changes in the lung that can be demonstrated as a low ratio (<0.7) of forced expiratory volume in 1s (FEV1) to forced vital capacity (FVC).,
Various risk factors of COPD in developing countries likely differ from those in developed ones. Although tobacco smoking rates are different in these countries, exposure to biomass fuels, cooking indoors, high tuberculosis prevalence, and different age structure have a relevant influence on COPD epidemiology. According to World Health Organization report 2014, one-third of the world's population were using biomass fuel, including wood, crop residues, such as straw and sticks, dried leaves, twigs, wild grass, animal dung, or charcoal, for cooking and/or heating. The smoke from these biomass fuels had a clear roll in the incidence of COPD.
Smoking and exposure to environmental tobacco smoke have been proved to be the strongest risk factors for airflow obstruction, but many areas of the world with high mortality rates from “COPD” still have low consumption of tobacco, implying that tobacco smoking alone does not explain the distribution of COPD.,, In our previous studies, we found that the prevalence of airflow limitation was higher in individuals who had ever smoked or been passive-smoker,, but was prevalent in never-smokers as well. Iran is a developing country where the smoking rate is lower than in many developed countries.
It has been proved that 90% of COPD deaths occur in developing countries in the future and 40% of these deaths are attributable to tobacco smoking, notwithstanding a high prevalence of COPD in some of developing countries. The burden of COPD in developing countries seems to be high because of several reasons including challenges with COPD diagnosis, increased exposures to risk factors, relatively low COPD awareness, and combustion products of biomass fuels.
The international, population-based Burden of Obstructive Lung Disease (BOLD) Initiative was designed to develop robust models during last 2 decades, which can be used to estimate the prevalence and current and future economic burden of COPD. It is undoubtedly crucial that geographic distribution and variation of COPD occurrence provide national data for quality of public health activities and clinical health care services.
The objectives of this study were to estimate the prevalence, clinical characteristics, disease severity, previous physician diagnosis, management of COPD, and a comparison of urban and rural communities in Mazandaran Province, Iran.
| Methods|| |
The BOLD study protocol in Iran was published elsewhere.
Population and sampling strategy
We used the same sampling protocol consistently throughout the project. The sampling frame in this study was the whole population of Mazandaran Province located in the north of Iran. The present population in this area was ~3 million.
Drawing upon our experience, a design effect of 1.5, prevalence rate of 50%, and a response rate of 90%, the total sample size was calculated by 385 in 2 different sexes for ≥40 years of age, and 385 for 18–39 years.
This study followed a stratified cluster sampling strategy with proportional allocation within strata. The target population was all noninstitutionalized inhabitants, aged 18–40 in one group and >3 in another, who inhabited in urban or rural areas of Mazandaran in 2016.
The stratification of the sample according to the 19 cities of Mazandaran Province was incorporated in the sampling process. The appropriate number of clusters was weighted according to each city. The decision about the number of clusters was on the basis of total sample size; mean household members; and logistical facilities for subject enumeration, transport, and examination.
For each cluster, a team of 3 members (1 male and 1 female aged <28 as interviewers dressed in white medical overall and a driver) approached the index household, which was specified through the aforementioned random selection of clusters, and continued the enumeration in 10 neighbor households in a systematic manner by proceeding round in a clockwise direction. In an indexed household, if there was >3 person, then interviewers were advised to use the Kish method to choose the right participant(s).
The examination protocol included a questionnaire covering respiratory symptoms, health status, activity limitation, and exposure to potential risk factors, such as tobacco smoke, occupational risk factors, and biomass exposure. They also performed pre- and postbronchodilator spirometry tests. Spirometry records provide the 1-s and 6-s forced expiratory volumes (FEV1 and FEV6) and the FVC.
The Core questionnaire was developed from pre-existing validated questionnaires that had already been used in multinational studies. The questionnaire obtains information about respiratory symptoms, exposure to potential risk factors, including smoking, occupation, respiratory diagnoses, comorbidities, health care utilization, medication use, activity limitation, and health status.
Participants also were expected to complete an occupational questionnaire and (for current cigarette smokers) a ''stages of change'' questionnaire that assessed readiness to quit smoking. There was also a questionnaire to assess exposure to biomass fuels used in the home for either heating or cooking. All questionnaires were translated to Persian first and then back-translated to English by a different translator. The questionnaires were administered by trained and certified staff; self-administration of questionnaires was not allowed.
The single most important outcome measure obtained as part of this protocol was spirometry before and after administration of 200 mg (2 puffs) of salbutamol. To optimize quality control in this study, all teams were required to use the 2120 In2itive Vitalograph Spirometer, which was chosen because it provides an acceptable degree of accuracy, robustness, portability, and ease of storage. It can be used easily in the field and where there is no electric power available. The 2120 In2itive Vitalograph Spirometer had been approved by National Research Institute of Tuberculosis and Lung Diseases as meeting predetermined performance criteria relating to the reliability of measurement, suitability for field use, and ease of access to data.
COPD definitions were: (1) spirometry: postbronchodilator FEV1/FVC ratio <70%; (2) prior medical diagnosis: an affirmative response to: “Have you ever had chronic bronchitis, emphysema, or COPD confirmed by a doctor?”; and (3) clinical definition: positive criteria for the standard definition of chronic bronchitis. These definitions allowed comparison without any need for reference values and were a widely used standard that can be compared with other published studies.,
Humanity and ethics
The study has been approved by the Research and Ethics Committee of Shahid Beheshti University of Medical Sciences and Ethics Committee of National Research Institute of Tuberculosis and Lung Disease since 2014.
The descriptive statistics for categorical variables were included the number and percent and for continues variables were included the mean ± SD. The prevalence was calculated by proportion and compared by the χ2 test. To evaluate the factor associated with COPD by criteria, univariate and multivariate logistic regression analyses were performed. All statistical analyses were performed by SPSS 19 software and 0.05 was considered as significant level.
| Results|| |
A total of 1007 subjects were included in the study. Among under study participants, 500 (49.7%) subjects were males and 507 (50.3%) were females. The mean age of participants was 44 ± 14.16 years and their other characteristics are presented in [Table 1].
COPD and symptoms
There are 266 (26.4%) subjects with dyspnea including 123 (48.1%) in villages and 143 (51.9%) in cities, 200 (19.95%) with chronic cough (51.5% in cities and 48.5% in villages), and 220 (21.8%) with sputum production (48.2% in cities and 51.8% in villages). Among all participants, only 5 (0.5%) subjects had a prior medical diagnosis of COPD, 46 (5%) subjects had COPD on the basis of symptoms and 43 (8.3%) subjects had COPD on the basis of spirometry criteria. The frequency distribution of subjects according to the latter diagnosis criteria by demographic and also potential important factors are presented in [Table 2]. Exposure to dust and fumes at workplace rates was higher in rural areas than in urban areas (47 (9.6%) vs 28 (5.4%), P < 0.0001). The rates of having an open fire with wood, crop residues or dung as a primary means of heating your home for >3 months, and of cooking were both higher in rural areas areas (106 (21.5%) vs 87 (16.9%) P < 0.0001 and 116 (23.6%) vs 89 (17.4%) P < 0.0001, respectively).
The prevalence of COPD on the basis of symptoms in males (58.7%) was similar to females (41.3%) (P = 0.19) and in the over 40 years of age (65.1%) was more than the under 40 years of age (34.9%) (P = 0.04). The prevalence of COPD on the basis of spirometry in males (51.2%) and females (48.8%) was nearly the same (P = 0.88) and in over 40 years (97.6%) was more than the under 40 years (2.4%) (P< 0.001). The prevalence of COPD on the basis of symptoms among the urban areas (45.7%) and the rural areas inhabitants (54.3%) was approximately the same (P = 0.55). On the basis of spirometry, the prevalence of COPD among the urban areas inhabitants (34.9%) was less than the rural areas (65.1%) (P = 0.02).
Factor associated with COPD
According to univariate logistic regression, the risk of COPD on the basis of symptoms in current smokers was more than never-smokers (OR: 2.40; 95% CI: 1.30–4.44) and in urban inhabitants is less than rural inhabitants (OR: 0.48; 95% CI: 0.24–0.95). Subjects with exposure to dust and fumes at the workplace had a higher risk of COPD compared with subjects without exposure (OR: 2.46; 95% CI: 1.35–4.50). According to multivariate analysis, current smokers (OR: 1.93; 95% CI: 1.02–3.67) and subjects with exposure to dust (OR: 2.07; 95% CI: 1.09–3.81) had significantly higher COPD risk.
For COPD diagnosed by spirometry in the univariate analysis, urban inhabitants in comparison with rural inhabitants had lower COPD risk (OR: 0.48; 95% CI: 0.24–0.95)). Subjects who were smoker had a higher risk compared with subjects who were not (OR: 1.97; 95% CI: 1.01–3.82). The risk of COPD for subjects with exposure to dust (OR: 2.07; 95% CI: 1.09–3.94), subjects with chronic bronchitis (OR: 2.36; 95% CI: 1.13,4–93) and subjects with asthma (OR: 8.03; 95% CI: 3.84–16.77) was higher compared with its contrary status. In the multivariate analysis, no significant association was found [Table 3].
| Discussion|| |
The present cross-sectional survey of 1007 adults was the first systematic epidemiological study of COPD prevalence and risk factors comparing urban and rural communities in Iran. The estimates of risk factors presented here were on the basis of the age range starting from 18 years, and spirometric screening of COPD was on the basis of people aged ≥40 years. All participants were living in 19 different cities and 19 villages near the main cities.
The study showed that the prevalence of previously diagnosed COPD reported by respondents was 0.5%, and the total prevalence according to the global initiative for chronic obstructive lung disease criteria was 8.3% (95% CI: 6.26%–11.06%). This difference has proved the benefit of spirometric screening of COPD using the postbronchodilator fixed ratio of FEV1/FVC <0.7 as a discriminating criterion., The observations from this study were similar to the results found in many other countries with an expected range of 4%–10% using spirometry,, though it was higher compared with previously reported findings from Western Pacific and South East Asia., This figure is considerably close to our previous results in Iran.,
Mazandaran Province has diverse nature stretching from the sandy beaches of the Caspian Sea to the rugged and snowcapped Alborz sierra. Although this region experiences windy climate but is known as one of the most densely populated. However, the exact impression of these assumptions needs further investigation.
In this study, rural residents had significantly higher rates of COPD on the basis of spirometry than urban residents. These differences could be because of socioeconomic variations between urban and rural areas that provide unequal opportunities to improve participants' standard of living. A meta-analysis by Adeloye et al. revealed that across world regions, urban dwellers had higher COPD prevalence rates (13.2%; 95% CI: 11.8%–14.7%) than rural populations (10.2%; 95% CI: 8.2%–12.2%), and over a period of 20 years between 1990 and 2010, the percentage of rise in COPD cases was higher among urban inhabitants than among rural residents.
The relationship between lung health status and habitation location is complex and depends on factors such as; occupational exposures, lifestyle, and differences in access to health care.
Results of our investigation suggests a significant relationship between exposure to dusts and fumes at workplace, having an open fire with wood, and using crop residues or dung as a primary means of heating or cooking with the prevalence of COPD in urban and rural areas, like some studies in this field,, We did not find any differences between tobacco smoking in rural and urban areas, but rural residence were more exposed to other environmental and occupational risk factors for COPD such as fuel-fired power plants and agricultural work. Moreover, rural communities had a higher proportion of older inhabitants, which could explain higher rates of COPD in these participants. Jackson et al. found higher hospitalization rates among rural compared with urban inhabitants. Abrams et al. revealed higher mortality among veterans living in isolated rural areas likewise.
In this study, the rate of COPD diagnosed by spirometry, and on the basis of symptoms, had a tendency to increase with age. This phenomenon could be explained by the physiological decrease in lung function and greater exposure to environmental and occupational risk factors with age. Brachier et al. did not find any association between chronic bronchitis and increasing age in a study conducted in Pune slums in India. Our finding similar to a large number of previous epidemiological studies showed a high prevalence of COPD in the elderly and the rate of COPD sufferers had a gradual increase with increasing age.,,
Prevalence of tobacco smoking in our study was similar to previous researches. A statistically significant relationship was shown between smoking and COPD similar to previous reports.,,, The risk of COPD depends on the number of consumed cigarettes and the duration of smoking. It has been proved that any amount of tobacco is harmful, although the risks could be lower at low quantity. Chhabra et al. showed that the prevalence of chronic respiratory diseases among smokers with >3.5 pack-years was higher. Similarly, Mahesh et al. reported that prevalence of COPD in smokers with <20 pack-years was 9.6%, which increased to 18% in subjects who smoked >3 pack-years. It seems that there is a strong relationship for cigarette smoking and COPD, with no evidence of a threshold. Interestingly, in our study, around two-thirds of COPD participants were never-smokers. There was increasing evidence on the occurrence of COPD in nonsmoking individuals showing an estimation of 25%–45% of patients with COPD have never smoked tobacco. The rate of COPD in never-smokers suggests that, besides tobacco smoking, other risk factors such as genetic factors, impaired lung growth, infections and environmental exposures including occupational exposures and (outdoor and indoor) air pollution might contribute to the development of COPD.,
The strengths of this study were similar to other BOLD studies across the world enjoying a population-based sampling frame derived from 19 different cities and 19 different villages in a province and collecting data. In addition, measurements of the variables in this study were done independently of the research question, which made it less prone to information and selection bias.
| Conclusions|| |
In conclusion, these results added to the growing literature on geographic disparities among patients with COPD and provided evidence that the prevalence of COPD, in general, tends to be higher in the rural community. However, both rural and urban groups were equally underdiagnosed and undertreated.
This study showed that occupational and environmental smoke exposure was associated with COPD. A new design of preventive strategies especially must be done to cooking energy and cooking stoves, particularly in rural areas.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Adeloye D, Chua S, Lee C, Basquill C, Papana A, Theodoratou E, et al
. Global and regional estimates of COPD prevalence: Systematic review and meta-analysis. J Glob Health 2015;5:020415.
GOLD Executive Summary. Global Initiative for Chronic Obstructive Lung Disease. Global strategy for the diagnosis management and prevention of chronic obstructive pulmonary disease. Updated 2014. Global Initiative for Chronic Obstructive Lung Disease; 2014.
Cruz AA. Global surveillance, prevention and control of chronic respiratory diseases: A comprehensive approach. World Health Organization; 2007.
Nugmanova D, Feshchenko Y, Iashyna L, Gyrina O, Malynovska K, Mammadbayov E, et al
. The prevalence, burden and risk factors associated with chronic obstructive pulmonary disease in Commonwealth of Independent States (Ukraine, Kazakhstan and Azerbaijan): Results of the CORE study. BMC Pulm Med 2018;18:26.
Gupta D, Agarwal R, Aggarwal AN, Maturu VN, Dhooria S, Prasad KT, et al
. Guidelines for diagnosis and management of chronic obstructive pulmonary disease: Joint recommendations of Indian chest society and national college of chest physicians (India). Indian J Chest Dis Allied Sci 2014;56:5-54.
Haahtela T, Tuomisto LE, Pietinalho A, Klaukka T, Erhola M, Kaila M, et al
. A 10 year asthma programme in Finland: Major change for the better. Thorax 2006;61:663-70.
Vestbo J, Hurd SS, Agustí AG, Jones PW, Vogelmeier C, Anzueto A, et al
. Global strategy for the diagnosis, management, and prevention of chronic obstructive pulmonary disease: GOLD executive summary. Am J Respir Crit Care Med 2013;187:347-65.
Eisner MD, Anthonisen N, Coultas D, Kuenzli N, Perez-Padilla R, Postma D, et al
. An official American Thoracic Society public policy statement: Novel risk factors and the global burden of chronic obstructive pulmonary disease. Am J Respir Crit Care Med 2010;182:693-718.
Organisation mondiale de la santé. Lignes directrices OMS relatives à la qualité de l'air intérieur: Consommation domestique de combustibles; 2014.
Raj TJB. Altered lung function test in asymptomatic women using biomass fuel for cooking. J Clin Diagn Res 2014;8:1-3.
Hooper R, Burney P, Vollmer WM, McBurnie MA, Gislason T, Tan WC, et al
. Risk factors for COPD spirometrically defined from the lower limit of normal in the BOLD project. Eur Respir J 2012;39:1343-53.
Salvi SS, Barnes PJ. Chronic obstructive pulmonary disease in non-smokers. Lancet 2009;374:733-43.
Gilkes A, Hull S, Durbaba S, Schofield P, Ashworth M, Mathur R, et al
. Ethnic differences in smoking intensity and COPD risk: An observational study in primary care. NPJ Prim Care Respir Med 2017;27:50.
Wilson D, Adams R, Appleton S, Ruffin R. Difficulties identifying and targeting COPD and population-attributable risk of smoking for COPD: A population study. Chest 2005;128:2035-42.
Sharifi H, Masjedi MR, Emami H, Ghanei M, Eslaminejad A, Radmand G, et al
. Burden of obstructive lung disease study in Tehran: Prevalence and risk factors of chronic obstructive pulmonary disease. Lung India 2015;32:572-7.
] [Full text]
Sharifi H, Ghanei M, Jamaati H, Masjedi MR, Aarabi M, Sharifpour A, et al
. Burden of obstructive lung disease study in Iran:First report of the prevalence and risk factors of copd in five provinces. Lung India: Official Organ of Indian Chest Soc 2019;36:14.
Sharifi H, Sadr M, Emami H, Ghanei M, Eslaminejad A, Radmand G, et al
. Prevalence of tobacco use and associated factors in Tehran: Burden of obstructive lung disease study. Lung India 2017;34:225-31.
] [Full text]
Barnes PJ. Chronic obstructive pulmonary disease: A growing but neglected global epidemic. PLoS Med 2007;4:e112.
Mehrotra A, Oluwole AM, Gordon SB. The burden of COPD in Africa: A literature review and prospective survey of the availability of spirometry for COPD diagnosis in Africa. Trop Med Int Health 2009;14:840-8.
Buist AS, Vollmer WM, Sullivan SD, Weiss KB, Lee TA, Menezes AM, et al
. The burden of obstructive lung disease initiative (BOLD): Rationale and design. COPD 2005;2:277-83.
Sharifi H, Masjedi MR, Emami H, Ghanei M, Buist S. Burden of obstructive lung disease study in Tehran: Research design and lung spirometry protocol. Int J Prev Med 2014;5:1439-45.
Binson D, Catania JA. Random selection in a national telephone survey: A comparison of the Kish, next-birthday, and last-birthday methods. J Official Statistics 2000;16:53.
Buist AS, McBurnie MA, Vollmer WM, Gillespie S, Burney P, Mannino DM, et al
. International variation in the prevalence of COPD (the BOLD Study): A population-based prevalence study. Lancet 2007;370:741-50.
Soriano JB, Zielinski J, Price D. Screening for and early detection of chronic obstructive pulmonary disease. Lancet 2009;374:721-32.
Menezes AM, Perez-Padilla R, Jardim JR, Muiño A, Lopez MV, Valdivia G, et al
. Chronic obstructive pulmonary disease in five Latin American cities (the PLATINO study): A prevalence study. Lancet 2005;366:1875-81.
Regional COPD Working Group. COPD prevalence in 12 Asia-Pacific countries and regions: Projections on the basis of the COPD prevalence estimation model. Respirology 2003;8:192-8.
Kim SJ, Suk MH, Choi HM, Kimm KC, Jung KH, Lee SY, et al
. The local prevalence of COPD by post-bronchodilator GOLD criteria in Korea. Int J Tuberc Lung Dis 2006;10:1393-8.
Teckle P, Hannaford P, Sutton M. Is the health of people living in rural areas different from those in cities? Evidence from routine data linked with the Scottish Health Survey. BMC Health Serv Res 2012;12:43.
Liu XL, Lessner L, Carpenter DO. Association between residential proximity to fuel-fired power plants and hospitalization rate for respiratory diseases. Environ Health Perspect 2012;120:807-10.
Greskevitch M, Kullman G, Bang KM, Mazurek JM. Respiratory disease in agricultural workers: Mortality and morbidity statistics. J Agromedicine 2007;12:5-10.
Jackson BE, Coultas DB, Suzuki S, Singh KP, Bae S. Rural-Urban disparities in quality of life among patients with COPD. J Rural Health 2013;29:s62-9.
Abrams TE, Vaughan-Sarrazin M, Fan VS, Kaboli PJ. Geographic isolation and the risk for chronic obstructive pulmonary disease–related mortality: A cohort study. Ann Inter Med 2011;155:80-6.
Brachier B, Londhe J, Madas S, Vincent V, Salvi S. Prevalence of self reported respiratory symptoms asthma and chronic bronchitis in a slum area of a rapidly developing Indian city. Open J Respir Dis 2012;2:73-81.
Carlsson AC, Wändell P, Ösby U, Zarrinkoub R, Wettermark B, Ljunggren G. High prevalence of diagnosis of diabetes, depression, anxiety, hypertension, asthma and COPD in the total population of Stockholm, Sweden–A challenge for public health. BMC Public Health 2013;13:670.
LeVan TD, Koh WP, Lee HP, Koh D, Yu MC, London SJ. Vapor, dust, and smoke exposure in relation to adult-onset asthma and chronic respiratory symptoms: The Singapore Chinese Health Study. Am J Epidemiol 2006;163:1118-28.
Bjartveit K, Tverdal A. Health consequences of smoking 1–4 cigarettes per day. Tob Control 2005;14:315-20.
Chhabra SK, Rajpal S, Gupta R. Patterns of smoking in Delhi and comparison of chronic respiratory morbidity among beedi and cigarette smokers. Indian J Chest Dis Allied Sci 2001;43:19-26.
Mahesh PA, Jayaraj BS, Prahlad ST, Chaya SK, Prabhakar AK, Agarwal AN, et al
. Validation of a structured questionnaire for COPD and prevalence of COPD in rural area of Mysore: A pilot study. Lung India 2009;26:63.
] [Full text]
Lange P, Celli B, Agustí A, Boje Jensen G, Divo M, Faner R, et al
. Lung-function trajectories leading to chronic obstructive pulmonary disease. New Eng J Med 2015;373:111-22.
[Table 1], [Table 2], [Table 3]