Introduction

Chronic obstructive pulmonary disease (COPD) is a preventable and treatable disease characterized by chronic progressive airflow limitation that is not fully reversible. As a global health problem, COPD is a major cause of morbidity and mortality worldwide. Today, COPD ranks 6th among all causes of death and it is projected to be the 3rd leading cause of death in 2020 [1].

COPD prevalence is below 1% in all age groups according to the World Health Organization [2]. Recently, parallel with increased smoking rates and a progressive aging of the population, COPD prevalence has risen progressively [3]. The increase of tobacco marketing strategies in developing countries has caused COPD prevalence to rise worldwide [4]. Smoking is the most important risk factor for COPD. Since the majority of smokers start smoking at adolescent age, influence of society is very important at this period. Adolescents are influenced by friends and teachers who are role-models for them [5]. Therefore, smoking attitudes of teachers are especially important for our future generations and for the achievement of the goal of a smoke-free population. Unfortunately, although the data are limited, recent studies have found that smoking rates in teachers in Turkey were from 36.2% to 52.4% [6–10]. As a result of this high smoking rate, it was thought that COPD prevalence might be high in teachers. The aim of this study was to evaluate smoking and COPD prevalence amongst teachers working in the schools of Kocaeli City.

Materials and methods

Study population

In this cross-sectional population-based study, teachers who accepted to join the study and could perform an acceptable spirometer maneuver were included in the study. Cases that did not have appropriate questionnaire data or could not perform an acceptable spirometer maneuver were excluded from the study.

Study design

Teachers who work in Kocaeli were informed about the study aim and design. In this prospective study, the European Community Respiratory Health Survey (ECRHS) questionnaire [11] investigating respiratory symptoms and smoking habits was administered to all participants who accepted to join the study. All subjects underwent a physical examination and a pulmonary function test was performed with portable spirometer (Koko Legend portable spirometer; Ferraris Med, Co, USA). Spirometer calibration was checked daily with a 3-L syringe.

The pulmonary function test was performed according to American Thoracic Society (ATS) criteria by a trained technician with participants in a seated position [12]. Participants performed up to 8 forced expiratory maneuvers to obtain three acceptable maneuvers (difference between largest and second largest values < 200 ml for both forced expiratory volume in 1 sec [FEV1] and forced vital capacity [FVC]). If the participants were tired or had not an acceptable maneuver, the test was stopped.

Values of FVC, FEV1, FEV1/FVC, forced expiratory flow (FEF)25-75 were evaluated in the pulmonary function test. Patients with airflow limitation (FEV1/FVC < 70%) received four puffs (100 mcg each) of salbutamol sulfate administered via a spacer (Volumatic®) and spirometry was performed after 20 minutes. An increase by 12% or 200 ml of the post-bronchodilator FEV1 value with respect to baseline FEV1 was defined as reversible [1, 13, 14]. Cases with reversible airway obstruction and a history suggestive of asthma were excluded while cases that had irreversible airway obstruction were accepted as COPD and medical treatment and follow up were planned for them. Spirometry was evaluated as small airway obstruction if FEF25-75 level was lower than 70% predicted. Cases that had FEV1/FVC ratio greater than 70% with a FVC level lower than 80% predicted were defined as restrictive.

The study was approved by the Kocaeli University Medical Faculty Ethics Committee and all subjects gave their informed consent.

Case definitions

COPD

Post-bronchodilator FEV1/FVC of less than 70% without reversibility was accepted as COPD whether there were respiratory symptoms or not.

Chronic bronchitis

It was defined as cough and sputum production for at least 3 months of 2 consecutive years.

Asthma

Cases with reversible airway obstruction were accepted as asthmatic if their history was consistent with asthma, and they were excluded from the analysis.

Subjects with reversible airflow obstruction without respiratory complaints and subjects with chronic respiratory symptoms with normal lung function were invited to our out-patient clinic for further investigation, and excluded from the analysis. Furthermore all smokers were recommended to a smoking cessation clinic after medical advice to quit smoking.

Statistical analysis

Statistical analysis was performed with the SPSS 13.0 program. Data are reported as mean ± standard deviation. Student's t test and Mann Whitney-U test were used to compare data between groups. Chi-square test was used for the comparison of rates and proportions. A p value of 0.05 or lower was considered significant.

Results

A total of 685 teachers were included in the study. Of these 307 were female (45%) and 378 were male (55%). Mean age was 38.9 ± 8.9 years, and 296 subjects (43.2%) were over the age of 40. The mean age and the number of cases older than 40 years were significantly higher in males than females. Demographic data of the study population is shown in Table 1.

Table 1 Demographic characteristics of participants
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Smoking habits were evaluated in 660 subjects, of which 291 (44.1%) were smokers, 252 (38.2%) non-smokers, and 117 (17.7%) ex-smokers. The percentage of current smokers was 43.2% in females and 44.8% in males. There was no statistically significant difference between male and female smokers (p = 0.6).

It was found that 161 subjects (23.5%) had a smoking history over 10 years (103 men, 58 women). There was a statistically significant difference between genders for smoking history over 10 years (p = 0.001).

The mean number of cigarettes smoked in a day was 5.7 ± 8.9 (min: 1, max: 40) and there was a statistically significant difference between genders (males 6.5 ± 9.9, females 4.7 ± 7.3, p = 0.001). In the study there was a considerably large range in the number of cigarettes smoked. So the standard deviation was higher than average. It was found that 76 male (21.3%) and 34 female (11.5%) smokers had a daily consumption of cigarettes over 20. Smoking characteristics according to gender are shown in Table 2.

Table 2 Smoking characteristics according to gender
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Chronic bronchitis was found in 23 of 631 participants (3.8%) and 73.9% of these cases were smokers. There was a statistically significant difference in smoking rates between chronic bronchitis and non-chronic bronchitis cases (p = 0.007). Only two of the chronic bronchitis cases were diagnosed as COPD. No significant relation was found with COPD.

Pulmonary function tests were available in 651 subjects and 510 of them (78.3%) were defined as normal spirometric analysis. Mean values of FEV1 and FEF25-75 revealed a significant difference between genders (FEV1% predicted: male 100.9 ± 14.6 vs. female 98.6 ± 13.0, p = 0.03; FEF25-75%: male 94.4 ± 25.9 vs. female 83.6 ± 20.7, p = 0.001). Small airway obstruction was found in 115 subjects (17.7%) in whom FEF25-75 level was found to be lower than 70% predicted. Comparison of pulmonary function tests between males and females is shown in Table 3.

Table 3 Comparison of pulmonary function tests between males and females
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FEV1/FVC level was lower than 70% in 16 subjects (2.5%). Five subjects who had a positive reversibility test were excluded from the study. The remaining 11 subjects (6 of whom were aged over 40) were considered as COPD and consisted of 2 females (18%) and 9 males (82%) (Table 4). All of the cases diagnosed as COPD were current or ex-smokers.

Table 4 Pulmonary function test results according to gender
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Discussion

This study demonstrates high smoking rates and a considerably high prevalence of COPD in a relatively young population consisting of teachers. Different COPD definitions can influence the reported prevalence rates. COPD prevalence varies according to epidemiologic definition [17, 18] and the local variability of risk factors and other unknown conditions [19, 20].

The global burden of COPD was evaluated in a systematic meta-analysis by Halbert and co-workers. The most common spirometric definition was that of GOLD and the pooled prevalence of COPD was 7.6% from 37 studies [21].

Lindberg et al. evaluated COPD prevalence among 666 participants aged 20-69 years. COPD prevalence was 7.6, 14, 14.1, 12.2, and 34.1% according to, respectively, British Thoracic Society (BTS), European Respiratory Society (ERS), GOLD, clinical and spirometric ATS criteria. Prevalence of COPD was related to age and smoking habits but not to gender [22].

Menezes et al. evaluated COPD prevalence according to symptoms, GOLD and ERS criteria. They showed that chronic bronchitis prevalence by questionnaire data was 7.8% and COPD prevalence was 15.2% according to GOLD. COPD was higher among men, elderly and ex-smokers [15].

The PREPOCOL study evaluated COPD prevalence for different altitudes, in 5 Colombian cities.

A respiratory questionnaire was administered and pre-post bronchodilator spirometry performed in 5,539 participants who were over 40 years of age. The overall COPD prevalence was 8.9, 2.8, 3.2% using the spirometric, medical and clinical definitions. The factors related to COPD were age over 60 years, male gender, smoking and low educational level. The overall prevalence of active smoking was 18.3%, higher in men (24.4%) than in women (15.3%) [16].

In our study, COPD was defined by clinical and spirometric data according to GOLD criteria. Chronic bronchitis symptoms were found in 23 of 631 participants (3.8%), a finding in line with Caballero et al. Our study's COPD prevalence according to GOLD was 2%, which was lower than other studies. But smoking prevalence in our study was higher than that of Caballero et al. and there was no difference between male and female gender.

Recently, the Burden of Lung Disease (BOLD) assessment was created for a standardized evaluation of the burden of COPD. The BOLD questionnaire included information on respiratory symptoms and risk factors for COPD and pre-post bronchodilator spirometry performed in BOLD studies. The Australian BOLD study included 1,258 participants older than 40 years of age, and the overall prevalence of COPD at stage I and higher was found to be 26.1%, similar in males and females. Smoking prevalence was 19.2% and also showed no difference between genders [13]. In the BOLD study in Iceland (ISOLD study), COPD prevalence was 18%, and there was no difference between males and females. The prevalence of COPD increased with age and the amount of tobacco smoked [23]. The BOLD study carried out in Poland's Mapolska region showed that COPD prevalence was 22.1% and higher in men than women. Smoking prevalence was 28% (males: 36.1%, females: 21.9%) [14]. In the BOLD study in China, 20,245 participants completed both a questionnaire and spirometry. The overall prevalence of COPD was 8.2% (males: 12.4%, females: 5.1%) [24].

In our study, the method used to detect COPD - a questionnaire that included respiratory symptoms and smoking habits and post-bronchodilator spirometry performed in each participant - was similar to that of the BOLD studies. Also COPD definition was according to GOLD criteria. But the COPD prevalence found in our study (2%) was lower than that of BOLD studies. This might be related to our limited study population.

COPD prevalence is 0.934% in men, 0.733% in women (all age groups) according to the World Health Organization [3]. Recently, in parallel with increased smoking rates and the growing age of the population, COPD prevalence is rising progressively [4]. Furthermore it was thought that the increase of COPD prevalence in women was related to increased smoking rates. While there were no differences in COPD prevalence between gender in some of these studies [13, 22, 23], in our study COPD prevalence was higher in men than in women, in agreement with other studies [14–16, 24].

Epidemiologic data on COPD are limited in our country. In particular, there are no data on occupation and COPD. COPD prevalence, risk factors and burden of disease were evaluated in the Adana BOLD study by Kocabaş et al. in the period December 2003-January 2004. Preliminary results of this study showed that COPD prevalence was about 20% in subjects over 40 years of age in Adana [25].

Örnek et al. evaluated 611 participants who were > 18 years of age by respiratory questionnaire and spirometry (evaluated according to GOLD criteria) in order to determine the prevalence of COPD in Zonguldak. COPD prevalence was found to be 15.2% in the overall population and it was 17.8% regarding the subjects > 40 years of age [26].

Günen et al. evaluated COPD prevalence in a population randomly selected from urban and rural regions of Malatya. Through a respiratory questionnaire and post-bronchodilator spirometry performed in 1,160 participants over the age of 18, COPD prevalence was found to be 6.9%. While the prevalence of COPD was 18.1% in current smokers, the prevalence was 4.5% among young smokers. Biomass exposure was significantly common (54.5%) among female subjects living in rural areas. Smoking prevalence was 57.2% in men, 25.5% in women [27].

In our study, COPD prevalence (2%) was found to be lower than in other studies carried out in our country. This might be related to the fact that our study population features one occupational group and so may not project all characteristics of society. When COPD prevalence was evaluated according to gender, we found a male predominance, a similar result to other studies in our country. But, in contrast to Günen et al., smoking prevalence was similar in both males and females in our study.

In conclusion, COPD is a preventable and treatable disease. Spirometry has an important role in early diagnosis of COPD. Spirometric evaluation of cases with risk factors for COPD could be helpful to diagnose patients before the progressive decline in lung function begins. Further studies are needed to evaluate whether interventional strategies at this stage such as smoking cessation could prevent the progression of disease.

Conflict of interest statement

None of the authors has any conflict of interest to declare in relation to the subject matter of this manuscript.