Tafa H, Mema D, Mezini A, Nikolla J, Teferici A, Todri D, et al. Prevalence of chronic obstructive pulmonary disease (COPD) in Albania (Original research). SEEJPH 2021, posted: 09 February 2021. DOI: 10.11576/seejph-4164 P a g e 1 | 12 ORIGINAL RESEARCH Prevalence of chronic obstructive pulmonary disease (COPD) in Albania Holta Tafa1, Donika Mema2, Arian Mezini1, Jolanda Nikolla3, Alma Teferici1, Dafina Todri1, Genc Burazeri4, Hasan Hafizi1 1 University Hospital “Shefqet Ndroqi”, Tirana, Albania; 2 Institute of Public Health, Tirana, Albania; 3 American Hospital, Tirana, Albania; 4 Faculty of Medicine, University of Medicine, Tirana, Albania. Corresponding author: Hasan Hafizi, MD, PhD; Address: Rr. “Shefqet Ndroqi”, Tirana, Albania Telephone: +355697491518; Email: hasanhafizi@hotmail.com Tafa H, Mema D, Mezini A, Nikolla J, Teferici A, Todri D, et al. Prevalence of chronic obstructive pulmonary disease (COPD) in Albania (Original research). SEEJPH 2021, posted: 09 February 2021. DOI: 10.11576/seejph-4164 P a g e 2 | 12 Abstract Aim: The objective of this study was to determine the prevalence of COPD and its associated factors among adults in Albania. Methods: This was a cross-sectional study conducted in Albania in 2013-14. A nation-wide rep- resentative sample of 1200 adults aged ≥40 years was selected using multistage cluster sampling technique. All participants were interviewed about socio-demographic characteristics, respiratory symptoms, smoking status and clinical characteristics. Spirometry was performed according to standard methods. COPD was defined as post-bronchodilator FEV1/FVC ratio <70% predicted. Results: Of the 1200 adults invited to participate, 939 adults or 78% (467 men and 472 women) were eligible for the study. The overall COPD prevalence (GOLD stage 1 or higher) was 12.4%; it was higher in men (17.4%) than in women (7.7%). Using Lower Limit of Normal (LLN), the prevalence of COPD was 9.9%, again higher in men (13.2%) than women (6.6%). The prevalence of doctor-diagnosed COPD was 1.3% (1.9% in men, 0.6 % in women). Male sex, smoking and increasing age were significantly associated with COPD diagnosis. Conclusion: The overall prevalence of COPD in Albania was 9.9% using BOLD standards. Smok- ing and increasing age were the main risk factors for COPD. The study highlights the importance of raising awareness of COPD among health professionals. Keywords: Albania, BOLD study, COPD prevalence, risk factors. Conflicts of interest: None declared. Tafa H, Mema D, Mezini A, Nikolla J, Teferici A, Todri D, et al. Prevalence of chronic obstructive pulmonary disease (COPD) in Albania (Original research). SEEJPH 2021, posted: 09 February 2021. DOI: 10.11576/seejph-4164 P a g e 3 | 12 Introduction Chronic Obstructive Pulmonary Disease (COPD) is currently the fourth leading cause of death in the world but is projected to be the 3rd leading cause of death by 2020 (1). Glob- ally, the COPD burden is projected to in- crease in coming decades because of contin- ued exposure to COPD risk factors and aging of the population (2). COPD prevalence, morbidity and mortality vary across countries and across different groups within countries. COPD is the result of a complex interplay of long-term cumula- tive exposure to noxious gases and particles, combined with a variety of host factors in- cluding genetics, airway hyper-responsive- ness and poor lung growth during childhood (3,4). Often, the prevalence of COPD is di- rectly related to the prevalence of tobacco smoking, although in many countries out- door, occupational and indoor air pollution (resulting from the burning of wood and other biomass fuels) are major COPD risk factors (5,6). Despite a growing burden, COPD is often a neglected disease and its epidemiology is largely unknown in particular in low and middle income countries (7). Existing COPD prevalence data vary widely due to differ- ences in survey methods, diagnostic criteria and analytical approaches (2). Many patients with COPD are still underdiagnosed, inade- quately evaluated and under-recognized lead- ing to significant underreporting of the dis- ease (8,9). Community based studies using appropriate methods are needed to determine the epide- miology of COPD and to enable the develop- ment of prevention and management strate- gies for the future. The Burden of Obstructive Lung Disease (BOLD) initiative aimed at developing and using a standardized method to measure the prevalence of COPD and its risk factors in various areas around the world (10,11). In our study, we used BOLD protocol to esti- mate the prevalence and burden of COPD in Albania. Methods BOLD developed standardized methods in- cluding standardized spirometry equipment, meticulous quality control measures, stand- ard protocols, validated and translated ques- tionnaires and standard data entry and analy- sis. BOLD Operations Centre (OC) emphasized data quality control at every stage of the pro- cess. The study was conducted in close colla- boration with the BOLD Operations Centre (OC) in London which provided oversight, training, materials, quality control, and data analysis. National Bioethics Committee’s approval was a prerequisite for study implementation. Study design This was a cross-sectional study conducted in Albania in 2013-14, which consisted of a COPD prevalence survey among adults aged ≥40 years. A representative sample of adult individuals in this age range was asked to fill in the questionnaires and perform spirometry tests designed by BOLD. Target population and sampling procedure: A nation-wide representative sample was drawn. A multi-stage cluster sample of 1200 individuals (600 men and 600 women) aged ≥40 years was drawn based on the sampling frame (alias the target population) available from the national Institute of Statistics (INS- TAT). BOLDOC in London, UK, reviewed and approved the sampling approach calcu- lated by a local expert. Recruitment of participants: Participants were contacted through home visits and were Tafa H, Mema D, Mezini A, Nikolla J, Teferici A, Todri D, et al. Prevalence of chronic obstructive pulmonary disease (COPD) in Albania (Original research). SEEJPH 2021, posted: 09 February 2021. DOI: 10.11576/seejph-4164 P a g e 4 | 12 asked to provide an informed consent to schedule a clinic visit and where necessary. Study Measures Spirometry was performed by eight trained and certified technicians (EasyOne spirome- ter; ndd Medizintechnik; Zurich, Switzer- land). COPD was defined as a post-broncho- dilator FEV1/FVC <70% predicted. Spirom- etry data were sent electronically to the OC where each spirogram was reviewed and graded using ATS guidelines (12). Post bronchodilator spirometry tests were performed at least 15 min after achievement of at least 3 acceptable and 2 reproducible pre bronchodilator spirometry tests. The number of pack-years of cigarette smok- ing was defined as the average number of cig- arettes smoked per day divided by 20 (i.e., packs per day) times the duration of smoking in years. Data recording and analysis Data for BOLD study consisted of electroni- cally generated spirometry records, responses to questionnaires administered to study par- ticipants, individual tracking data, and aggre- gate data about the target population. Our data were reported to OC for validation and analysis. Estimated population prevalence of COPD for the overall city population was computed using survey data methods in Stata v. 12 (Stata Corporation, College Station, TX, USA), and stratified by sex, age and smoking status. The study was conducted from October 2012 to December 2013. Results Of the 1200 adults invited to participate, 997 (83%) of them were eligible for the study. Among them 11 participants were excluded because of lost spirometry data due to the faulty spirometer and 47 other participants due to unacceptable post BD spirometry. Table 2 shows that there were no differences between responders and non-responders who were eligible for the study, except for smok- ing status and other co-morbid conditions (p<0.001 and p<0.007, respectively). Partici- pants that were current smokers and those with co-morbid conditions were less likely to be responders. Table 3 shows the prevalence of smoking in Albania by sex and age. Overall, 21.6% of in- dividuals ≥40 years old were smokers at the time of the study. Smoking was much more prevalent in males than in females. The per- centage of smoker was higher in age group 50-59. The overall prevalence of GOLD stage I or higher COPD was 12.4%, and was higher in male (17.4%) than female sex (7.7%) and in those >70-year old. Using Lower Limit of Normal (LLN) the prevalence of COPD was 9.9%, again higher in males (13.2%) than females (6.6%) and like using GOLD criteria was higher in indi- viduals > 70 years old (Table 4). The prevalence of COPD was strongly re- lated to smoking history expressed as pack years as shown in table 5. Table 6 shows the prevalence of smoking in Albania by sex and age. Overall, 21.6% of individuals ≥ 40 years old were smokers at the time of the study. Smoking was much more prevalent in males than in females. The percentage of smokers was higher in age group 50-59. The prevalence of doctor- diagnosed COPD was much lower than spi- rometry-confirmed COPD, with an overall estimate of 1.3% (1.9% in males, 0.6 % in females) (Table 28). It was higher in group >70 years. Tafa H, Mema D, Mezini A, Nikolla J, Teferici A, Todri D, et al. Prevalence of chronic obstructive pulmonary disease (COPD) in Albania (Original research). SEEJPH 2021, posted: 09 February 2021. DOI: 10.11576/seejph-4164 P a g e 5 | 12 Table 1. Disposition of Study Participants for BOLD SITE: Tirana, Albania Outcome Men Women Unknown Total Responders: Full data collected (Core Ques plus QC acceptable post BD spirometry) 467 472 0 939 Full data collected (Core Ques plus QC unacceptable post BD spirometry) 27 20 0 47 Full data collected (Spirometry data lost due to faulty spirometer)* 2 9 0 11 Total responders 496 501 0 997 Non-responders: Partial data collected 51 49 0 100 Refused (minimal data collected) 2 2 0 4 Refused (no minimal data collected) 43 32 0 75 Known to have temporarily left area 3 10 0 13 Unreachable (couldn’t reach)† 4 5 0 9 Total non-responders 103 98 0 201 Ineligible: Deceased 1 1 0 2 Permanently left catchment area 0 0 0 0 Age ineligible 0 0 0 0 Institutionalized 0 0 0 0 Untraceable (bad address & phone)‡ 0 0 0 0 Total ineligible 1 1 0 2 Total selected for recruitment¶ 600 600 0 1200 * Some spirometry data was lost before it could be transferred, due to a faulty spirometer; † Contact information apparently correct, but no response to contact attempts; ‡ Contact information incorrect, no updated information available; ¶ Number of responders + non-responders + ineligibles. Table 2. Comparison of responders* and non-responders† for Albania Responders Non-responders P-value‡ Age 40-49 351 (36%) 81 (40%) 0.382 50-59 330 (33%) 55 (27%) 60-69 191 (19%) 40 (20%) 70+ 114 (12%) 25 (12%) Gender Male 494 (50%) 103 (51%) 0.768 Female 492 (50%) 98 (49%) Smoking status Current 213 (22%) 46 (23%) <0.001 Ex 148 (15%) 9 (4%) Never 625 (63%) 146 (73%) Doctor diagnosed asthma, emphysema, CB or COPD Yes 64 (6%) 6 (3%) 0.056 No 922 (94%) 194 (97%) Other co-morbid conditions Yes 260 (26%) 72 (36%) 0.007 No 726 (74%) 129 (64%) * Responders are those who completed post-BD spirometry (regardless of QC scores) and the core questionnaire. † Non-responders are eligible individuals who are missing the core questionnaire and/or post-BD spirometry, but for whom the tabulated variable is known. ‡ Two-sided p-value based on Pearson’s chi-square test Tafa H, Mema D, Mezini A, Nikolla J, Teferici A, Todri D, et al. Prevalence of chronic obstructive pulmonary disease (COPD) in Albania (Original research). SEEJPH 2021, posted: 09 February 2021. DOI: 10.11576/seejph-4164 P a g e 6 | 12 Table 3. Estimated Population Prevalence (SE) of GOLD Stage 1 or higher COPD* by age and sex for Albania Age-group Sex 40-49 50-59 60-69 70+ Total Male 3.8 (0.5) 10.0 (2.3) 28.4 (6.7) 52.5 (7.5) 17.4 (2.5) Female 2.3 (0.5) 4.1 (1.9) 17.0 (6.1) 14.7 (5.2) 7.7 (2.3) Total 3.0 (0.4) 7.0 (1.5) 22.4 (4.7) 32.3 (4.9) 12.4 (1.7) * Post-BD FEV1/FVC <70%. Table 4. Estimated Population Prevalence (SE) of COPD in Tirana, Albania, using Lower Limit of Normal (LLN): Modified Stage 1 or higher COPD* by age and sex (Local Equations) Age-group Sex 40-49 50-59 60-69 70+ Total Male 4.2 (0.9) 5.3 (2.3) 21.2 (2.2) 41.2 (11.0) 13.2 (2.6) Female 3.8 (1.4) 4.1 (1.9) 12.3 (5.5) 10.7 (2.4) 6.6 (1.4) Total 4.0 (0.8) 4.7 (1.5) 16.5 (3.2) 24.9 (5.4) 9.9 (1.4) * Post-BD FEV1/FVC < LLN Table 5. Estimated Population Prevalence (SE) of GOLD Stage 1 or higher COPD* by pack years and sex in Tirana, Albania Pack-years Sex Never smokers 0-10 10-20 20+ Total Male 6.2 (2.2) 10.2 (4.8) 7.6 (2.3) 27.6 (4.6) 17.4 (2.5) Female 6.1 (2.9) 19.8 (18.9) 24.2 (11.5) 9.0 (8.4) 7.7 (2.3) Total 6.1 (2.1) 14.8 (9.5) 14.3 (5.5) 27.0 (4.5) 12.4 (1.7) * Post-BD FEV1/FVC < 70% and post-BD FEV1 < 80% predicted Table 6. Prevalence of current smoking by age and sex in Tirana, Albania Age-group Sex 40-49 50-59 60-69 70+ Total Respond- ers with usable data* Male 40.5% 44.6% 29.3% 21.0% 35.8% Female 7.8% 8.4% 5.3% 3.0% 7.3% Total 22.5% 23.6% 19.9% 15.8% 21.6% Popula- tion† Male 44.5% (5.2) 46.7% (1.7) 29.4% (5.6) 21.1% (7.8) 38.7% (3.2) Female 6.5% (3.2) 8.3% (1.8) 4.8% (4.2) 5.2% (4.5) 6.5% (0.9) Total 25.3% (3.2) 27.9% (1.0) 17.1% (4.4) 12.4% (4.0) 22.4% (1.8) * Non-weighted data for the sample of responders. † Weighted population estimate, with SE shown in parenthesis. Tafa H, Mema D, Mezini A, Nikolla J, Teferici A, Todri D, et al. Prevalence of chronic obstructive pulmonary disease (COPD) in Albania (Original research). SEEJPH 2021, posted: 09 February 2021. DOI: 10.11576/seejph-4164 P a g e 7 | 12 Table 7. Estimated Population Prevalence (SE) of Doctor-Diagnosed COPD* by age and sex in Tirana, Albania Age- group Sex 40-49 50-59 60-69 70+ Total Male 0 1.7 (1.4) 3.8 (1.8) 4.4 (2.6) 1.9 (0.8) Female 0 2.3 (0.7) 0 0 0.6 (0.1) Total 0 2.0 (0.8) 1.9 (0.9) 2.0 (1.2) 1.3 (0.4) * Includes chronic bronchitis, emphysema or COPD Discussion This is the first COPD prevalence study ever conducted in Albania. Response rate for Al- bania was high, both for males and females, 82.3%. Response rates among females were slightly higher, 84% as compared to 83% for males, although not statistically significant. We did not observe any difference among the responders according to age groups, doctor diagnosed asthma, emphysema, chronic bronchitis (CB) or COPD, but we found sta- tistically significant difference in relation to smoking status and other co-morbid condi- tions. The percentage of responders and non- responders among current smokers was simi- lar, showing that completing questionnaires and performing spirometry was not easy for a current smoker. The percentage of never smokers for non-responders and responders was respectively 73% and 63%, (p<0.001), showing that never smokers are less concer- ned about respiratory health status. Among participants with co-morbid conditions, the percentage of non-responders and responders was respectively 64% and 74%, (p<0.007), showing that presence of co-morbid condi- tions is likely to increase awareness about respiratory health status. Our study showed that the overall COPD prevalence (GOLD stage 1 or higher) in Al- bania was 12.4%, and was higher in males (17.4%) than females (7.7%) and in those aged > 70 years old. Using Lower Limit of Normal (LLN) the prevalence of COPD was 9.9%, again higher in males (13.2%) than fe- males (6.6%) and like when using GOLD cri- teria, was higher in those aged > 70 years old. Thus, the prevalence of COPD using LLN was lower than the prevalence estimated us- ing GOLD criteria. The Global Initiative for Chronic Obstructive Lung Disease (GOLD) uses a fixed ratio of FEV1/FVC of 0.7 for the diagnosis of ob- struction by spirometry, regardless of age, sex or height (13). This may result in false- positive diagnose of COPD in elderly sub- jects, as the ratio has a small but significant age related regression (14). The ATS/ERS task force has recommended the use of Lower Limit of Normal (LLN) rather than a fixed ra- tio to avoid overdiagnosis of COPD (15). In our study we used LLN for that purpose. A literature review of the epidemiology of chronic obstructive pulmonary disease showed that the prevalence estimates varied widely, depending on the methods used for diagnosis and classification of COPD (16- 18). The reported prevalence of COPD ranged from 0.2% in Japan to 37% in USA (19). Another systematic review for Europe coun- tries showed that prevalence estimates varied from 2.1% to 26.1%, depending on country, age group and methods used (20). Comparing our data to the international BOLD studies we conclude that COPD pre- valence in Albania is lower than that reported from many other countries like: Austria Tafa H, Mema D, Mezini A, Nikolla J, Teferici A, Todri D, et al. Prevalence of chronic obstructive pulmonary disease (COPD) in Albania (Original research). SEEJPH 2021, posted: 09 February 2021. DOI: 10.11576/seejph-4164 P a g e 8 | 12 26.1% (21); Iceland 18% (22); Germany 13.2% (23), and higher than that of other countries like: China 8.2% (24) and Australia 7.9% (25). These geographical differences, despite the use of the BOLD protocol, could be at- tributed to different levels of smoking in the local population, or possibly other risk fac- tors, such as genetic predisposition, occupa- tion, biomass and air pollution. Our study showed a significant correlation between age and smoking history expressed as pack years (r = 0.500; p < 0.001). The as- sociation of COPD with old age may be at- tributed to a greater exposure to risk factors (26,27). The prevalence of COPD in women in our study was lower than in men like in most of the countries worldwide due to the fact that women traditionally smoke much less than men (28). This situation has changed in some developed countries, where the prevalence of smoking in women is now often as high as that in men (29). The prevalence of COPD in never smokers was surprisingly similar for both men and women, which differs from that of most of the studies. The high prevalence of COPD among women in most of the developing countries is at- tributed to biomass and cooking conditions (30-32). In Albania it does not appear to be a major contributory factor. The prevalence of smoking in our study was 21.6%. It was higher in males than females, 35.8% and 7.3% respectively. The highest prevalence was in age groups 50-59 and 40- 49 years; there was a trend for smoking ces- sation with increasing age. We think that this fact is related to the co-morbidities that asso- ciate the age group above 60 years old. An important fact is noted in relation to female smoking status. In females over 40 years smoking was not as prevalent as in males in population. This is related to the fact that our society is a conservative one. But this trend has changed for younger generations: in fe- males under 40 years old an increase in smok- ing prevalence was observed. Our study showed that the prevalence of smoking was 17% in group age 20-39, as compared to 7.3% in other group ages above 40 years old. This high percentage was found mainly in the urban areas, whereas in rural areas smoking prevalence in this group age did not differ compared to other group ages. The preva- lence of COPD in the smoker group (both for- mer and current smoker) was found to be much higher than that in the non smoker group. Similar findings were reported in most studies and cigarette smoking is the most common risk factor for COPD worldwide (26,33). Consistent with the present understanding of the role of smoking, we found a strong dose- response relationship with pack-years of smoking (27,34). As found in other studies there was also a positive trend with the increasing of pack- years, confirming smoking as an important risk factor for disease development (35,36). Our data showed a low prevalence of doctor diagnosed COPD reported by participants, only 1.3% and this finding was similar to most of the countries where under-diagnosis of COPD is common (37). But there are countries where prevalence of doctor-diagnosed COPD was higher like in South Arabia 9.8% (38) and in Salzburg, Austria 5.6% (39). Skipping spirometric confirmation of COPD, thus leading to over-diagnosis, might be the reason behind reported data in South Arabia (38). Our data are consistent with those of other countries where there is still a high level of under-diagnosis. The need for spirometry Tafa H, Mema D, Mezini A, Nikolla J, Teferici A, Todri D, et al. Prevalence of chronic obstructive pulmonary disease (COPD) in Albania (Original research). SEEJPH 2021, posted: 09 February 2021. DOI: 10.11576/seejph-4164 P a g e 9 | 12 testing should be brought to the attention of primary care physicians. Our study has several strengths. This is the first study conducted in Balkan areas using BOLD protocol. Moreover, we applied the BOLD protocol with standardized methodol- ogy and high-quality post-BD spirometry. Such standardized methodology included standardized spirometry equipment, meticu- lous quality control measures, standard pro- tocols, validated questionnaires and standard data recording, reporting and analysis. Moreover, the use of a large sample size rep- resents the whole country. Conclusion We found that the prevalence of COPD among adults in Albania was high, with an estimated prevalence of 12.4% in adults ≥40 years old; 17.4% and 7.7% in men and women respectively. Using LLN, the preva- lence of COPD was lower, 9.9% (13.2% and 6.6% in men and women respectively). COPD prevalence was strongly related to smoking and national smoking cessation pol- icies are needed. Doctor diagnosed COPD reported by the par- ticipants was very low. These numbers clearly show a high degree of COPD under- diagnosis and highlight the need to improve physicians’ knowledge about COPD diagno- sis and greater use of spirometry References 1. Lozano R, Naghavi M, Foreman K, Lim S, Shibuya K, Aboyans V, et al. Global and regional mortality from 235 causes of death for 20 age groups in 1990 and 2010: a system- atic analysis for the Global Burden of Disease Study 2010. Lancet 2012;380: 2095-128. 2. Mathers CD, Loncar D. Projections of global mortality and burden of disease from 2002 to 2030. PloS Med 2006;3:e442. 3. Lange P, Celli B, Agustí A, Boje Jensen G, Divo M, Faner R, et al. Lung-Function Trajectories Leading to Chronic Obstructive Pulmonary Disease. N Engl J Med 2015;373:111-22. 4. Tashkin DP, Altose MD, Bleecker ER, Connett JE, Kanner RE, Lee WW, et al. The lung health study: airway responsiveness to inhaled methacholine in smokers with mild to moderate airflow limitation. Am J Respir Crit Care Med 1992;145:301- 10. 5. Eisner MD, Anthonisen N, Coultas D, Kuenzli N, Perez-Padilla R, Postma D, et al. An official Ameri- can Thoracic Society public policy statement: Novel risk factors and the global burden of chronic obstructive pulmonary disease. Am J Resp Crit Care Med 2010;182:693-718. 6. Salvi SS, Bames PJ. Chronic ob- structive pulmonary disease in non- smokers. Lancet 2009;374:733-43 7. Van Gemert FA, Kirenga BJ, Ge- bremariam TH, Nyale G, de Jong C, van der Molen T. The complications of treating chronic obstructive pul- monary disease in low income coun- tries of sub-Saharan Africa. Expert Rev Respir Med 2018;12:227-37. 8. Rabe KF, Hurd S, Anzueto A, Barnes PJ, Buist SA, Calverley P, et al. Global strategy for the diagnosis, management, and prevention of chronic obstructive pulmonary dis- ease: GOLD executive summary. Tafa H, Mema D, Mezini A, Nikolla J, Teferici A, Todri D, et al. Prevalence of chronic obstructive pulmonary disease (COPD) in Albania (Original research). SEEJPH 2021, posted: 09 February 2021. DOI: 10.11576/seejph-4164 P a g e 10 | 12 Am J Respir Crit Care Med 2007;176:532-55. 9. Badway MS, Hamed AF, Yousef FM. Prevalence of chronic obstruc- tive pulmonary disease (COPD) in Qena governorate. Egypt J Chest Dis Tuberc 2016;65:29-34. 10. Buist AS, Vollmer WM, Sullivan SD, Weiss KB, Lee TA, Menezes AM, et al. The Burden of Obstruc- tive Lung Disease Initiative (BOLD): rationale and design. COPD 2005;2:277-83. 11. Crapo RO, Hankinson JL, Irvin C, MacIntyre NR, Voter KZ, Wise RA, et al. Standardization of spirom- etry, 1994 update. Am J Respir Crit Care Med 1995;152:1107-36 12. Global Initiative for Chronic Ob- structive Lung Disease. Global strat- egy for the diagnosis, management and prevention of chronic pulmonary disease, 2014. Bethesda, MD, USA: GOLD, 2014. 13. Celli BR, Halbert RJ, Isonaka S, Schau B. Population impact of dif- ferent definitions of airway obstruc- tion. Eur Respir J 2003;22:268-73. 14. Pellegrino R, Viegi G, Brusasco V, Crapo RO, Burgos F, Casaburi RE, et al. Interpretative strategies for lung function tests. Eur Respir J 2005;26:948-68. 15. Lindberg A, Jonsson AC, Rönmark E, Lundgren R, Larsson LG, Lundbäck B. Prevalence of chronic obstructive pulmonary disease ac- cording to BTS, ERS, GOLD, and ATS criteria in relation to doctor’s diagnosis, symptoms, age, gender, and smoking habits. Respiration 2005;72:471-9. 16. Hnizdo E, Glindmeyer HW, Petsonk EL, Enright P, Buist AS. Case defi- nitions for chronic obstructive pul- monary disease. COPD 2006;3:95- 100. 17. Vaz Fragoso CA, Concato J, McAvay G, Van Ness PH, Rochester CL, Yaggi HK, et al. The ratio of FEV1 to FVC as a basis for estab- lishing chronic obstructive pulmo- nary disease. Am J Respir Crit Care Med 2010;181:446-51. 18. Rycroft CE, Heyes A, Lanza L, Becker K. Epidemiology of chronic obstructive pulmonary disease: a lit- erature review. Int J Chron Obstruct Pulmon Dis 2012;7:457-94. 19. Atsou K, Chouaid C, Hejblum G. Variability of the chronic obstructive pulmonary disease key epidemiolog- ical data in Europe systematic re- view. BMC Med 2011;9:2-16. 20. Schirnhofer L, Lamprecht B, Vollmer WM, Allison MJ, Studnicka M, Jensen RL, et al. COPD preva- lence in Salzburg, Austria: results from the Burden of Obstructive Lung Disease (BOLD) Study. Chest 2007;131:29-36. 21. Benediktsdóttir B, Gudmundsson G, Jörundsdóttir KB, Vollmer W, Gísla- son T. Prevalence of COPD in Ice- land: the BOLD study. Laeknabladid 2007;93:471-7. 22. Geldmacher H, Biller H, Herbst A, Urbanski K, Allison M, Buist AS, et al. The prevalence of chronic ob- structive pulmonary disease (COPD) in Germany. Results of the BOLD study. Dtsch Med Wochenschr 2008;133:2609-14. 23. Zhong N, Wang C, Yao W, Chen P, Kang J, Huang S, et al. Prevalence of Tafa H, Mema D, Mezini A, Nikolla J, Teferici A, Todri D, et al. Prevalence of chronic obstructive pulmonary disease (COPD) in Albania (Original research). SEEJPH 2021, posted: 09 February 2021. DOI: 10.11576/seejph-4164 P a g e 11 | 12 chronic obstructive pulmonary dis- ease in China: a large, population based survey. Am J Respir Crit Care Med 2007;176:753-60. 24. Toelle BG, Xuan W, Bird TE, Abramson MJ, Atkinson DN, Burton DL, et al. Respiratory symptoms and illness in older Australians: the Bur- den of Obstructive Lung Disease (BOLD) study. Med J Aust 2013;198:144-8. 25. Raherison C, Girodet PO. Epidemi- ology of COPD. Eur Respir Rev 2009;18:213-21. 26. Alam DS, Chowdhury MA, Sid- diquee AT, Ahmed S, Clemens JD. Prevalence and determinants of chronic obstructive pulmonary dis- ease (COPD) in Bangladesh. COPD: J Chron Obstruct Pulmon Dis 2015;12:658-67. 27. Kim DS, Kim YS, Jung KS, Chang JH, Lim CM, Lee JH, et al. Preva- lence of chronic obstructive pulmo- nary disease in Korea: a population- based spirometry survey. Am J Respir Crit Care Med 2005;172:842- 7. 28. Soriano JB, Maier WC, Egger P, Vi- sick G, Thakrar B, Sykes J, et al. Re- cent trends in physician diagnosed COPD in women and men in the UK. Thorax 2000;55:789-94. 29. Kiraz K, Kart L, Emir R, Oymak S, Gulmez I, Unalacak M, et al. Chronic pulmonary disease in rural women exposed to biomass fumes. Clin Invest Med. 2003;26:243-8. 30. Gordon SB, Bruce NG, Grigg J, Hib- berd PL, Kurmi OP, Lam KB, et al. Respiratory risks from household air pollution in low and middle income countries. Lancet Respir Med 2014;2:823-60. 31. Ramírez-Venegas A, Velázquez-Un- cal M, Pérez-Hernández R, Guzmán- Bouilloud NE, Falfán-Valencia R, Mayar-Maya ME, et al. Prevalence of COPD and respiratory symptoms associated with biomass smoke ex- posure in a suburban area. Int J Chron Obstruct Pulmon Dis 2018;13:1727-34. 32. Mannino DM, Buist AS. Global bur- den of COPD: risk factors, preva- lence, and future trends. Lancet 2007;370:765-73. 33. Salvi S, Barnes PJ. Is exposure to bi- omass smoke the biggest risk factor for COPD globally? Chest 2010;138:3-6. 34. Buist AS, McBurnie MA, Vollmer WM, Gillespie S, Burney P, Man- nino DM, et al. International varia- tion in the prevalence of COPD (the BOLD Study): a population-based prevalence study. Lancet 2007;370:741-50. 35. Vanfleteren LE, Franssen FM, Wes- seling G, Wouters EF. The preva- lence of chronic obstructive pulmo- nary disease in Maastricht, the Neth- erlands. Respir Med 2012;106:871-4. 36. Hill K, Goldstein RS, Guyatt GH, Blouin M, Tan WC, Davis LL, et al. Prevalence and underdiagnosis of chronic obstructive pulmonary dis- ease among patients at risk in pri- mary care. CMAJ 2010;182:673-8. 37. Al Ghobain M, Alhamad EH, Alorainy HS, Al Kassimi F, Lababidi H, Al-Hajjaj MS. The prevalence of chronic obstructive pulmonary dis- ease in Riyadh, Saudi Arabia: a BOLD study. Int J Tuberc Lung Dis 2015;19:1252-7. 38. Schirnhofer L, Lamprecht B, Vollmer WM, Allison MJ, Studnicka Tafa H, Mema D, Mezini A, Nikolla J, Teferici A, Todri D, et al. Prevalence of chronic obstructive pulmonary disease (COPD) in Albania (Original research). SEEJPH 2021, posted: 09 February 2021. DOI: 10.11576/seejph-4164 P a g e 12 | 12 M, Jensen RL, et al. COPD Preva- lence in Salzburg, Austria: Results from the Burden of Obstructive Lung Disease (BOLD) Study. Chest 2007;131:29-36. 39. Penña VS, Miravitlles M, Gabriel R, Jiménez-Ruiz CA, Villasante C, Masa JF, et al. Geographical varia- tions in prevalence and underdiagno- sis of COPD: Results of the IBER- POC multicentre epidemiological study. Chest 2000;118:981-9. ________________________________________________________________________________________ © 2021 Tafa et al; This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.