3.0. CHAPTER: PREVALENCE OF COPD

Transcription

1 CHAPTER: PREVALENCE OF COPD 3.1. REVIEW OF LITERATURE: Chronic obstructive pulmonary Disease (COPD) is a major but neglected public health problem and is a leading cause of death and disability worldwide. The WorldBank estimates that COPD is responsible for > 29 million disability-adjustedlife-years (DALYS) and 1 million years of life lost per annum aroundthe world. These figures place COPD as the fifth most significantglobal health problem, and COPD is expected to become the thirdleading cause of death in the first quarter of the next century Furthermore, COPD is currently the 12th leading cause of disabilityworldwide and is expected to be the fifth leading cause of disabilityby 2020 (Murray et al.,1996). Chronic Obstructive Pulmonary Disease: COPD is a clinical entity characterized by presence of airflow obstruction as revealed byirreversible decline of forced expiratory volume in one second (FEV 1 ), increasing presence of dyspnoea and other respiratory symptoms, presenting a slow and usually irreversible evolvement and progressive deterioration of health status. (J.M. Antó et al., 2001) Such airflow obstruction is invariably due to a pulmonary inflammatory response to noxious particles or gases. COPD is characterized by MRC criteria of cough with expectoration on most days of the week for three months of the year for at least two consecutive years.

2 Forced expiratory volume in one second (FEV 1 ) or (FEV 1 )/FVC value lower than 80% as diagnosed by spirometry indicates airway obstruction. More than 15% improvement in FEV 1 after administration of bronchodilators confirms bronchial asthma whereas in patients of COPD the bronchodilator reversibility test is negative. Grading ofcopd The GOLD (Global Initiative for Chronic Obstructive Lung Disease)has classified COPD as "a disease state characterized by airflowlimitation that is not fully reversible. The airflow limitationis usually both progressive and associated with an abnormalinflammatory response of the lungs to noxious particles or gases. (WHO, 2006) This definition has, in large part, been adopted in thenew American Thoracic Society (ATS guidelines), with the important observation that COPD isboth preventable and treatable (Celli BR et al., 2004) The GOLD criteria classify COPD into five stages: (WHO, 2006; Celli BR et al., 2004) Stage 0 At risk ( Normal spirometry, Chronic symptoms such as cough and sputum) Stage 1 - Mild (FEV 1 80% predicted with or without chronic symptoms, FEV 1 /FVC < 70%, patient not aware of the problem)

3 Stage 2 Moderate (50% FEV 1 < 80% predicted, FEV 1 /FVC < 70%,with or without chronic symptoms such as cough and sputum, shortness of breath on exertion, all patients seek medical attention) Stage 3 - Severe (30% FEV 1 < 50% predicted with or without chronic symptoms such as cough and sputum, FEV 1 /FVC < 70%, increased breathlessness, quality of life affected because of repeated exacerbations) Stage 4 Very severe (FEV 1 < 30% predicted or FEV 1 < 50% predicted + chronic respiratory failure with or without chronic symptoms such as cough and sputum, quality of life appreciably affected; exacerbations may be life threatening) Patho physiology of COPD: An inflammatory response in the airways and lung parenchymais an established feature of COPD and studies have shownthat small airways of COPD patients are persistently inflamedand that the intensity of the inflammatory process correlateswith the severity of COPD (Hogg JC et al., 2004). The inflammatory process is thought to play a central rolein mediating excess mucus secretion, fibrosis and proteolysis,which, in turn, lead to clinical phenotypes of chronic bronchitis,airway obstruction and emphysema. Once COPD is established, airwayinflammation persists, even after many years of smoking cessation (Rutgers SR et al., 2000). Several cell lines and inflammatorymediators are likely to be involved in the pathogenesis. Cigarettesmoke and other environmental irritants and infectious organismsmay activate alveolar macrophages, bronchial epithelial cells,and other cellular elements in the airways of genetically susceptibleindividuals (Barnes PJ et al.,

4 ). Once activated, these cells produce a varietyof signalling molecules, chemokines and cytokines, such as IL-8,which recruits neutrophils; macrophage chemotactic protein (MCP)-1,which recruits monocytes; and interferon- -inducible protein-10,which recruits lymphocytes. Additionally, they stimulate thesynthesis and release of growth factors, elastolytic enzymesand metalloproteinases, which, by themselves, may promote emphysematouschanges in lung parenchyma and airway remodeling (Barnes PJ et al., 2003)

5 Aetiology and risk factors of COPD: Aetiology of COPD is overwhelmingly dominated by smoking. Globally, the most important risk factor for COPD is thought to be smoking of tobacco (NHLBI/WHO, 2001). Environmental pollution, chemical exposure, inhaled smoke, passive smoking (Snigh N et al., 2002), exposure to biomass smoke (Smith KR et al., 2003) ), viral and bacterial infections, alpha-1-antitrypsin deficiency and other associated illnesses (pulmonary or not) are considered as important risk factors for the development of COPD (Figure 16). Phenotypic traits that are considered to play a role in the development of COPD include sex, with females being at a higher risk, bronchial responsivenesss and atopy. Many studies linking cigarette smoking and ETS to COPD have been carried out in the past and have served as in public places. Only recently, the the basis for regulation related to smoking linkages between other air pollutants and COPD have been recognized. Figure 16: Risk factors for COPD Prevalence of COPD: The global prevalence of COPD ranges from % (Table 13). A pooled prevalence of COPD of 7.6% has been estimated by systematic review illness in south Indian population

6 and meta analysis of 37 studies conducted in several countries between (R.J. Halbert et al., 2006).The prevalence of physiologically defined chronic obstructive pulmonary disease in adults aged > 40 yrs is around 9 10%. Prevalence of COPD in developed countries and from India are given in (Table 13 & Table 14).The prevalence in India ranges from as low as 1.2 to as high as 14% (Table 15). Table 13: Global Prevalence of COPD (Halbert RJ etl 2006) WHO region Prevalence % (Range) America 4.5 (3.2 14) Europe 8.3 ( ) South East Asia 12.5 ( ) Western Pacific 10.6 ( ) Table 14: Prevalence of COPD from developed countries Author Population Prevalence Men Women Overall Paul Stang et al., 2000 United States 14% - 46% J.M. Antóet al., 2001 USA Whites Blacks 4 6% 3.7% 1 3% 6.7% RJ Halbert et al., 2003 Italy 11% - 57% NikolaosTzanakis et al., 2004 Greece 11.6% 4.8% 8.4% Buist ASet al., sites in world 11.8% 8.5% 10.1%

7 Table 15: Prevalence of COPD in India Author Population Prevalence Overall Men Women Wig et al., 1964 Delhi Sikand et al., 1966 Delhi Viswanathan et al., 1966 Patna Bhattacharya et al., 1975 UP Joshi RC et al., 1975 North India 12.5% Radha et al., 1977 New Delhi Thiruvengadam et al., 1977 Chennai Viswanath& Singh, 1977 Delhi rural Delhi urban Charan, 1977 Punjab rural Viswanath& Singh, 1977 Delhi rural Delhi urban Malik, 1986 North India rural North India urban Jindal, 1993 North India rural North India urban Qureshi KA, 1994 Kashmir 7.7% Ray et al., 1995 South India Akhtar MA et al., 1999 Kashmir 14.12% (>70) Jindal SK etal., 2006 Bangalore, Chandigarh, Delhi, Kanpur 4.1% Indoor air pollution and COPD:

8 Corpulmonale, a heart condition that is secondary to COPD and that is also found among non-smoking rural women in south Asia (Smith KR, 1987), has long been attributed to long-term exposure to smoke from biomass (Padmavati and Pathak, 1959). Although, air pollution is commonly perceived as an urban problem that is associated with motor vehicles and industries, indoor air pollution caused by combustion of biomass fuels for household cooking virtually exposes about half of the world s population in rural areas of the developing countries to some of the highest levels of air pollution. Women exposed to indoor smoke are three times as likely to suffer from chronic obstructive pulmonary disease (COPD), such as chronic bronchitis, than women who cook and heat with cleaner fuels such as electricity and gas. A number of studies have examined various symptoms of chronic respiratory ill-health in women who cook with open stoves burning biomass (Smith KR, 2000). Studies from several countries have quantified the association between indoor air pollution and COPD. More recently systematic reviews and meta-analyses of the available epidemiological evidence has been completed for COPD (Kurmi et al., 2010) where positive associations was observed between the use of solid fuels and COPD (OR % CI ). A few studies from India (Behera& Jindal, 1991;Quereshi, 1994; Dutt et al., 1996) was included in the metanalysis by Kurmi etal The probable mechanisms by which cigarettesmoke, infectious organismsand other environmental irritants, particularly fine particulate indoor air pollution from biomass fuels could result in COPD is that they may activate alveolar macrophages, bronchial epithelial cells,and other cellular elements in the airways of genetically susceptibleindividuals. Once activated, these cells produce a varietyof signalling molecules, chemokines and cytokines, such as

9 IL-8,which recruits neutrophils; macrophage chemotactic protein (MCP)- 1,which recruits monocytes; and interferon-γ-inducible protein-10,which recruits lymphocytes. Additionally, they stimulate thesynthesis and release of growth factors, elastolytic enzymesand metalloproteinases, which, by themselves, may promote emphysematouschanges in lung parenchyma and airway remodeling. (Barnes PJ et al., 2003) There are important regional gaps, and methodological differences that hinder interpretation of the available data. Internationally, there is substantial variationin COPD prevalence possibly reflecting smoking behavior, type and processingof tobacco, outdoor and indoor pollution, climate, respiratory management, and geneticfactors. Though, several possible ways are usually applied to estimate the prevalence of COPD, estimatesbased on resource utilization may underestimate true prevalence and probably be biased towards the more severe and symptomaticcases. Moreover, estimates of COPD prevalence can also be hindered by unavailability of health-care data,inaccuracies incoding as well as inconsistent physician recognition of earlydisease. Thus, there is a need for a population-based epidemiologic study in our country designed to assess the true prevalence of COPD using standard definitions and objective measurements by spirometry. These findings can help health policy makers and providers, including physicians, to develop measures for better prevention and management of COPD in TamilNadu, Southern India. Moreover, it is also important to establish regional prevalence rates so that researchers and health professionals can monitor trends, implement interventions and evaluate the effectiveness of interventions. Therefore, this descriptive epidemiologic study was aimed to estimate the prevalence of

10 COPD in rural women of Tamilnadu and to identify the disease characteristics in Tamilnadu. Most of the studies have focused on prevalence of COPD in men who are smokers and rural women using bio fuels for cooking have not been well studied. Very few studies have attempted to examine the association between exposure to biomass smoke and the prevalence of COPD in rural populations especially women. The currently available estimates have been generated using secondary data on exposures and health outcomes provided by the Census and the National Family Health Survey respectively. Associations between bio-fuel exposure and increased incidences of chronic bronchitis in women have been documented (Pandey MR, 1984;Behera D, 1991). The investigator and the guide prior to this study have completed a separate pulmonary function assessment in normal apparently healthy South Indian rural women (Padmavathi etal., 2001) and also have demonstrated a decline in pulmonary function in women using biofuels (Sankar et al., 2001). The investigator and the guide involved in this proposal have been involved in the conduct of a large-scale exposure assessment exercise in Tamil Nadu wherein exposure assessment was conducted for members of 500 rural households across four districts of Tamil Nadu (Parik etal., 2001; Balakrishnan etal., 2002) and a similar exercise in three districts of Andhra Pradesh (Balakrishnan etal., 2003) has been completed and therefore are well aware of the technical inputs that would be required to execute this exercise. Currently few studies have attempted to examine the association between exposure to biomass smoke and the prevalence of COPD in rural populations especially women. The currently available estimates have been generated using secondary data on exposures and health outcomes provided by the Census and the National Family Health Survey respectively. There is a

11 need for a population-based epidemiologic study in our country designed to assess the true prevalence of COPD using standard definitions and objective measurements by spirometry. Therefore, this descriptive epidemiologic study was aimed to estimate the prevalence of COPD and to identify the disease characteristics in Tamilnadu which could also provide a framework for developing a multi-state/national exercise aimed at providing more precise national level estimates of the prevalence of COPD as well as it s linkages with biomass fuel use. There are differences in the prevalence rates based on age, gender, geographical` location and other demographic variables, time period of the study, methodology used for collection of data OBJECTIVE 3: Prevalence of Chronic Obstructive Pulmonary Disease in rural women 3.3. METHODS As the condition is a chronic outcome and there were no previous studies in this population, and the true prevalence was not available in this region, a cross sectional study design was chosen to estimate the prevalence of COPD in non smoking rural women of Tiruvallur district of Tamilnadu. The overall scheme of data generation illustrated below:

12 Ethical approval; Permissions; Preparation of study instruments; Training of the team Screening of women for COPD in households within the selected villages using a health & an exposure questionnaire Confirmation of COPD suspects by clinical and spirometric assessment Computing prevalence of COPD Data analysis; Presentation of results and submission of thesis Description of study area Thiruvallur district, a newly formed district bifurcated from the erstwhile Chengalpattu district (on 1st January 1997), is located in the North East part of Tamil Nadu. The population of the district is 27,38,866 persons with 51% male and 49% female as per the census 2001 (Census, 2001).The district has been divided into three revenue divisions viz, Tiruvallur, Tiruttani and Ponneri. There are three taluks under Thiruvallur division, two taluks under Tiruttani divisions and three taluks under Ponneri division (Figure 17) There are 46 firkas and 820 revenue villages. Likewise there are 14 blocks, 6 Municipalities and 19 town panchayats which implement rural development activities. Figure 17: Tiruvallur District Blocks and Taluks

13 Census of 2001, of India shows that about 71% of people use solid fuels and about 29% of people use liquid or District. other clean fuels for cooking in Tiruvallur Procurement of permissions Permission from Mr. Ranvir Prasad, the District Collector of the Tiruvallurr District, Tamil Nadu was obtained for conducting the study in 45 different villages in Tiruvallur District and for conducting air quality monitoring in select households. The study proposal with the informed consent forms (Annexure-II) and the household level questionnaire/ pro forma for recording self reported symptoms (Annexure-V) was submitted to the Institutional Ethics committee of SRMC&RI and the proposal was approved and cleared by the same (Annexure-I). Informed consent and the questionnaires were translated in the local language and validation. back translated in English for illness in south Indian population

14 Sample size for cross sectional study design A sample size of 900 individualswas calculated for this cross sectional study design based on the expected 10% prevalence of COPD and 80% power of accuracy with 95% confidence level. This was based on previous prevalence studies which showed wide variations ranging from 1.2% to 14.2% nationally, 1% to 57% internationally and 7.1 % to 17.9 % in South East Asia as per WHO Selection of representative zones within the study area for environmental and health data collection The sampling method adopted was cluster sampling based on probability proportion to size. In 45 different rural villages that had been selected by cluster sampling from 8 Taluks of Tiruvallur district, 20 females from each village were selected so that a total of 900 female subjects aged above 30 were recruited for this cross sectional study. The location of study zones is shown in Figure 18.

15 Figure 18: Map of Tiruvallur District area with study zones selected for data collection (8 taluks highlighted in 8 different colours and the select villages highlighted in red colour) Selection of subjects: The source population was from the villages of Thiruvallur district. Thiruvallur district has households comprising of a population of 2,738,866 persons with approximately an equal distribution of males and females. In each village that was selected by cluster sampling method, the centre of the village was located and by spinning a pencil and seeing the direction in which it stopped, the street in that particular direction comprising various households was selected. 20 females from that particular street of that village were selected for study so that a total of 900 female subjects aged above 30 were recruited for this cross sectional study. About 1087 household members were contacted to arrive at this target of 900. The subjects were selected as per the criteria mentioned below. Inclusion criteria: Females aged 30 yrs and above who are residents of the villages in Thiruvallur District for a minimum period of five years. Exclusion criteria: Bronchial asthma, Pulmonary Tuberculosis, Cardiac diseases, Pregnancy, HIV positive, Diabetes & Cancer Only onefemale member from each household was finally recruited to participatein the study. In case of more than one, a random selection was done

16 and the rest were rejected from the study. 71 subjects were rejected from the study accordingly. 10 subjects refused to participate though they were eligible for the study. Data collection Primary health data collection Every week on designated days, from the start of the study, households from different villages (select villages) in Tiruvallur district were visited according to the selection criteria described earlier and the study participants were recruited. Informed written consent was obtained before recruiting any person into the study. Once the persons gave informed consent, to be part of the study, the questionnaires were administered and part of health information was collected by eliciting a detailed history from the study participant and recorded in the appropriate fields of the health questionnaire (Annexure-V). A thorough clinical examination was done for all suspects of COPD cases and they were also subjected to PFT to confirm or rule out COPD. Assessment of pulmonary functions Study data was collected using a portable data logging Spiro meter. Pulmonary function tests were performed in a sitting position with nose closed by nose-clips following American Thoracic Society guidelines (ATS, 1995). Forced vital capacity (FVC), forced expiratory volume in one second (FEV 1 ), peak expiratory flow rate (PEFR), values were recorded. The values of the best of the three reproducible curves were taken. A complete flow-volume loop was obtained from the Spiro meter.most of the sources of variation in

17 pulmonary function assessment such as motivation and effort, body position were controlled. Spirometric testing including broncho dilation testing after inhalation of 200µgof Salbutamol, was carried out in order to rule out asthma and grade the COPD. A chest physician s opinion on the flow volume loops was also obtained to confirm the diagnosis. COPD cases were definedas follows: reversibility test result of < 15% improvementin FEV 1 compared to pre bronchodilator FEV 1 ; or post bronchodilatorimprovement of FEV 1 < 200 ml, and FEV 1 /FVC < 70% and nohistory of atopy or pattern of disease suggestive of asthma. Collection of exposure information variables studied: The variables of interest (both exposure and potential confounders) were collected through questionnaire from the study subject. The questionnaire (Annexure-V) included following variables: Main exposure variable of interest: Cooking fuel: wood/other biomass, dung cake, coal/charcoal, biogas, Liquefied Petroleum Gas (LPG), electricity. Kitchen location and ventilation in the kitchen and ventilation in other rooms Duration of cooking in various stoves and by fuel type

18 Tobacco smoking and Environmental Tobacco Smoke: Occupation Socio-economic status Marital status Statistical methods (Data handling, entry and analysis): All the data recorded on data forms were checked at the end of each day. The data were entered and random checks of entered data were reviewed for accuracy once each week. All the data collection forms were stored in locked cabinets in the department. Confidentiality was maintained. Study data was analyzed using the R statistical software. Prevalencerates were expressed in terms of percentage RESULTS: A total of 1,087 household members were contacted to arrive at a target of 900 subjects as per the sample size calculation. Descriptive statistics: Table 16provides important descriptive characteristics of the study population. Most study subjects (66%) were under the age of 50 while only a third of the subjects were above 50. Majority of the women were illiterate and of low socioeconomic status (with household income <Rs or $ 40 per month). Although only non-smoking women were included as study subjects, 25 % reported exposure to passive smoking from male smokers within their

19 household. Nearly 50% reported spending most of their time indoors on household chores and the rest reported working outdoor during the day. A highproportion of study participants used biomass as their primary fuel (83.7%) in unimproved stoves with only 16.3% using cleaner fuels like kerosene and LPG. Most households (~50% of study households) had indoor kitchens and the rest of the households were cooking outdoors most part of the year. The years of cooking ranged from 5 to 55 years with an average of 29.3 ± 11.2 years per woman. The mean time spent in cooking was 3.1 ± 1.2 hours per day. 40.3% were exposed to other particle sources such as mosquito coils and incense smoke. Although 45 participants reported to have positive symptoms such as chronic cough with phlegm, only 22 turned out to be COPD positive clinically and spirometrically. Distribution of the study population in the several descriptive categories was similar to distribution given in census data indicating the robustness of the data (Census, 2001). Table 16: Descriptive Characteristics of the study population Variables Frequency Percentage Fuel type Clean Biomass Kitchen type Outdoor Indoor Cooking duration < = 20 years >20 years < = 2 hours/day > 2 hours/day Passive smoking No

20 Variables Frequency Percentage Yes Main occupation Outdoor Indoor Person / room < = > House type Pucca/Semipucca Kutcha Age Literacy status Literate Illiterate Marital status Single / Widow Married Table 16 shows that the descriptive characteristics of the study population such as age, marital status, literacy status, socioeconomic status and occupation are representativesof the Tiruvallur district when compared with the Census data thereby proving the robustness of our data. Prevalence of COPD: Overall, 2.44% (1.43, 3.45) of the study participants (22 of 900 subjects)were diagnosed with COPD. Table 17 also provides the prevalence rates of COPD among several subcategories within the study population. Although the difference in prevalence of COPD across subcategories was not statistically significant, the differential prevalence across select subcategories

21 has been described to illustrate potential contributions from risks related to biomass fuel use. Prevalence of COPD was higher among the elderly women (>50 years), biomass users, women exposed to ETS, women who spent >2 hours/day in the kitchen for cooking and women who have been involved in cooking for more than 15 years. As seen in Table 16, the majority of women were biomass users with greater than 15yrs of cooking experience. Thus, although the observed differences in prevalence were all in the direction indicating an effect of biomass use, the sample lacked adequate power to detect statistically significant differences. Table 17: Prevalence rates of COPD by background characteristics of the study population of Tiruvallur district, TamilNadu Variables Prevalence rate (%) with 95%CI Overall prevalence 2.44% (1.43,3.45) Age Marital status Literacy status House type Person / room Kitchen type (0.73,2.87) (1.49,5.70) Single / Widow 3.5 (1.23,5.77) Married 2.0 (0.9,3.08) Literate 1.5 (-0.19,3.19) Illiterate 2.7 (1.5,3.9) Pucca/Semipucca 2.3 (1.04,3.56) Kutcha 2.5 (0.87,4.12) < = (1.09,3.61) > (0.91,4.29) Outdoor 2.4 (0.97,3.82) Indoor 2.5 (1.06,3.93)

22 Variables Prevalence rate (%) with 95%CI Fuel type Passive smoking Income Clean 2.0 (-0.26,4.26) Biomass 2.5 (1.38,3.61) No 2.3 (1.16,3.44) Yes 2.9 (0.74,5.1) > (0.69,6.1) < (1.13,3.27) < = 20 years 1.2 (-0.17,2.57) Cooking duration >20 years 2.9 (1.62,4.18) < = 2 hours/day 1.5 (0.5,2.5) > 2 hours/day 3.0 (1.16,4.84) Main occupation Outdoor 2.25 (0.87,3.63) Indoor 2.63 (1.16,4.1) 3.5.DISCUSSION: This large scale well designed, epidemiological cross section study with statistically calculated sample size has generated the prevalence of COPD, following the appropriate guidelines for diagnosis of COPD, in biomass fuel using rural women of Thiruvallur district of Tamilnadu. This is the first ever study conducted in this geographical location and in this category of vulnerable population. This first population-based epidemiological study of COPD that has been carried out in Tiruvallur district of TamilNadu showedthat the average prevalence of COPD in women> 30 years old is 2.44%.

23 The selection of the study population, and the proper definition are the two major limitations encountered in many surveys dealingwith prevalence of the disease in the general population in a cross sectional study: These limitations were minimized to a large extent in this study as we used a population-based design which avoided potentialselection biases, such as variations in accessinghealth care, geographicvariation within the district; and patient s occupational status. In orderto avoid sampling bias, women 30 years old were randomly identified in the villages selected by cluster sampling. Within each study region or site,individuals were also selected randomly, therefore, the final sample was representative of the Tiruvallur district. As the Tiruvallur district population characteristic is similar to the characteristics of overall Tamilnadu population, the study results can be extrapolated to the whole of Tamilnadu state. The methodology used here can also be applied by other investigators in other districts of Tamilnadu and other parts of the country. Comparisons with other studies: This population-based epidemiological study was carried out for estimating the prevalence of COPD, as there have been few community-based prevalence assessments for COPD in India, especially among non-smoking rural women and men and potential contributions from other risk factors such as biomass combustion and ETS have not been extensively studied. In a recent multi-centric study in India, prevalence of smoking in women was found to be only 2% with most of them residing in urban areas (Jindal SK, 2006) In this study a meticulous diagnostic approach was chosen foridentification of the COPD cases, including a completeclinical evaluation

24 with spirometry before and after bronchodilation, in order to minimize misclassificationof asthmatics as COPD cases. Few community-based studies have used such rigorous criteria. The prevalence estimate of COPD of 2.44% obtained in this study population of Indian, rural and primarily biomass using women of > 30 years of age is higher than the world prevalence of 0.8% (as reported by WHO). The prevalence in developed countries assessed mostly on smokers ranges from 4% to as high as 57% (Halbert RJ, 2003 & 2006). Prevalence estimates obtained in this study are similar to what has been reported in other Indian studies (Table 18) albeit slightly lower. The estimate is higher than what has been reported for an urban population in the neighbouring urban area in Chennai (Thiruvengadam, 1977). It is known that methodological differences are also responsible for differences in the prevalence rates. The reason for the differences in the prevalence rate observed in this study when compared with other studies could be due to several reasons such as most of them were hospital based studies where as this study is a population based study, inclusion of different ages where as women above 30yrs were chosen for this study; using different diagnostic method such as self reporting, without spirometric evaluation etc. However, while most studies are hospital based studies with higher smoking rates in the study population are likely to bias estimates towards higher prevalence, insufficient information on biomass use was available in most of the previous studies to make detailed comparisons. Further, biases resulting from use of alternative diagnostic protocols such as self reporting and evaluation without spirometry or without broncho-dilation that could all contribute to the differences in the prevalence observed between the studies could not be sufficiently examined. Prevalence of COPD in subjectsaged 50

25 years in the study sample was 3.6% ( ) as compared to subjects <50 years (1.8%).Although prevalenceof COPD in younger subjects is lower than in older individuals, it is of public health importance as the younger population witha long life expectancy will continue to be exposed to several risk factors such as biomass fuel use, passive smoking, and occupational exposures. As a result of the large reserves in human lung function andthe fact that COPD is a slowly progressive disease, the clinicaldiagnosis of COPD is often delayed until extensive and irreparabledamage has occurred. So young adults have to be targeted early by the health authorities to promote awareness of the disease and its risk factors and thereby reduce the morbidity and mortality due to COPD. The recognition of the true size of the problemand corresponding efforts to increase early identification of COPDcan help to reduce the morbidity and mortality that is associated withcopd in at-risk populations. Table 18: Prevalence of COPD from studies conducted in India Author Population Prevalence % in Women Thiruvengadam et al 1977 Chennai (urban) 1.2% Ray et al 1995 South India (rural) 2.5% Jindal SK et al 1993 North India (rural) 3.9% Jindal SKetal 2006 Multicentric (urban) 3.2% Present Study 2009 Tamilnadu (rural) 2.4% Implications for refining disease burden assessments attributable to biomass combustion:

26 This true prevalence estimate can also be used for calculation of global burden of COPD as COPD is the twelfth leading cause of disability worldwide with projected increase in its contribution over the next decade. The association between household biomass combustion and increased risk of COPD in rural women has been documented in many studies (Malik, 1985; Gupta B, 1997; Behera D, 1991; Perez Padilla, 1996; Dossing M, 1994; Dennis RJ, 1996) and has been used in the WHO lead comparative risk assessments (CRA) and burden of disease calculations in (Smith KR, 2000; Desai MA, 2004) An increasing body of evidence through animal studies also lends mechanistic support for this association. (Tesfaigzi Y,2005 ;Lal K, 1993) Most disease burden calculations have to rely on routinely collected secondary health data to estimate baseline prevalence. These estimates are often aggregated at the national level, masking differences that may exist across states in India both in terms of exposures and outcomes. An increasing body of exposure information now available on solid fuel using households across multiple states in India show that 24-hr household concentrations of RSPM from biomass combustion may range from 200 to 2000 µg/m 3 resulting in substantial differences in individual exposure across geographical regions.(balakrishnan, 2002, 2004 & 2006) With an increasing body of prevalence information across regions (states) where concomitant indoor pollution measurements are being made, it may be possible to increase the resolution of the association between biomass use and COPD prevalence across a continuum of population exposures. Moreover, it is difficult to estimate the effectiveness of an intervention in situations where pre intervention estimates of health parameter is inadequate,

27 which requires a demanding study design and analysis to examine or quantify causal associations.(benjamin F, 2010) Such baseline prevalence information in biomass using populations is also useful for future cross-sectional assessments that may be used to assess intervention efficacy or for making comparisons with other populations to frame an intervention. In conclusion, this cross-sectional population based study has estimated the COPD prevalence in a non-smoking, primarily biomass using rural women population, using objective lung function measurements in addition to clinical criteria. The burden of disease attributable to indoor air pollution has only been recently recognized as an important contributor to national burden of disease. Integration of the results from this study with exposure studies will help in refining disease burden estimates that are attributable to indoor air pollution. It is hoped that the baseline prevalence estimate for COPD generated in Tiruvallur district of Tamilnadu, can be used by the researchers as well as local public health officials in future for implementation of interventions to reduce the morbidity, mortality and economic burden due to COPD. The present study highlights the need to focus on the health infrastructure in rural areas. Efforts should be made to reduce the burden of COPD among patients from rural areas who constitute the bulk of cases and are economically poor. Limitation of the study: The sample size for COPD prevalence estimation was calculated using 10% prevalence, which is on the higher end of prevalence of COPD. Most of studies from India report a prevalence of about 2.5-4% amongst women, the overall prevalence being around 5 percent. Inadequate sample size is one of the limitations of this study. The results of this study can be viewed a pilot effort in

28 estimation of prevalence of COPD and can be used in the planning of future studies in this geographical region and women population.