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1 Dept of Lung Medicine and 3 The Research Unit, Örebro University Hospital, Örebro, 4 The Institute of Environmental Medicine, Karolinska Institutet, Stockholm, and 5 The OLIN studies, Dept of Medicine, Sunderby Central Hospital of Norrbotten, Luleå, Sweden. 2 Dept of Pulmonology, Institute of Experimental and Clinical Medicine, Tallinn, Estonia
CORRESPONDENCE: M.L. Larsson, Dept of Lung Medicine, Örebro University Hospital, SE-701 85 Örebro, Sweden. Fax: 46 19186526. E-mail: matz.larsson@orebroll.se
Keywords: asthma, epidemiology, passive smoking, respiratory symptoms
Received: April 25, 2002
Accepted November 28, 2002
This study was supported by grants from the Estonian Science Foundation, The National Health Institute, The Heart and Lung Foundation, and The Research Committee of Örebro County Council, Sweden.
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Abstract |
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In 1996, a postal questionnaire was randomly distributed in three areas of Estonia to a population-based sample, of which 4,995 females and 1,822 males had never smoked. The main outcome measures were current respiratory symptoms and the amount of reported ETS exposure outside the home.
ETS exposure at home was more common in females (31% versus 19%), while exposure outside of the home was more common in males (53% versus 7%). Females reported more symptoms from tobacco smoke than males (37.7% versus 21.6%). If ETS exposure outside of the home exceeded 5 h daily, the risk for wheeze (odds ratio (OR) 2.67, 95% confidence interval (CI) 1.98–3.61) and physician-diagnosed asthma (OR 1.79, 1.02–3.16) were increased. ETS exposure outside of the home was shown to be strongly related to almost all respiratory symptoms in a dose/response manner. ETS exposure at home did not show significantly elevated ORs for any respiratory symptoms.
This study shows that females seem to be more troubled by environmental smoke exposure than males and provides further evidence of the serious health hazards associated with environmental smoke exposure. Indeed, the findings of this study support a ban on smoking in the workplace and public areas.
The 1992 US Environmental Protection Agency (EPA) review 1 on passive smoking confirmed that exposure to environmental tobacco smoke (ETS), i.e. passive smoking, can cause respiratory illness in children. There is also increasing evidence of ETS causing respiratory illness in adults 2–11. The US EPA review also includes reports on a relationship between ETS, respiratory symptoms and sickness in adults 1. White et al. 7 showed that workplace ETS is more strongly related to respiratory symptoms than household exposure, a finding which has also been shown in other studies 8, 9. There are almost 4,000 chemical agents in ETS, including nicotine, carbon monoxide, benzene, formaldehyde, and acrolein, all of which are emitted from a burning cigarette and could cause respiratory symptoms 12. For many subjects with asthma, acute exposure to ETS is associated with respiratory symptoms 13 and ETS exposure has been reported to increase bronchial reactivity to histamine in asthmatics 14. Leuenberger et al. 8 reported on the increasing risk and dose relationship for respiratory symptoms related to total ETS exposure. In November 1999 the US National Cancer Institute published an extensive report 10 on health risks of ETS exposure. In the report, no definite conclusion on the association between ETS and chronic respiratory symptoms in adults was reached. Since this report, a dose relationship between exposure to ETS at work and respiratory symptoms in never-smokers, an important criterion for causal association, has been shown by others 9, 11. In the study by Lam et al. 11, performed on police officers with a small proportion of females, the association was clear among males but less clear among females. Studies concerning ETS and chronic respiratory symptoms in adults have mainly been performed on selected groups or with pooled data from many different countrys 9.
This study was conducted as a result of conflicting results in previous studies, lack of data from population-based random samples, lack of data from Eastern Europe and the scarcity of knowledge concerning females. The study's main aim was to examine the respiratory effects of ETS exposure in a random sample of adult never-smokers from a general population. A further aim was to study whether the respiratory effects of ETS exposure are different in males and females.
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Materials and methods |
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Study population
A random sample of 24,307 individuals stratified on a 10-yr age band and sex were selected from the populations of Tallinn (442,679 inhabitants), Narva (79,094 inhabitants) and Saaremaa (40,822 inhabitants). The Estonian State Computing Centre population register was used to identify subjects. This register is updated on a fortnightly basis. Smokers, former smokers, and subjects reporting "I don't leave home" were excluded. Prevalence rates of respiratory symptoms in this population have recently been reported 15.
Questionnaire
The questionnaire 16 was developed from a revised version of The British Medical Research Council questionnaire 17 and had been previously validated and used in several Scandinavian studies. The postal questionnaires were sent to the study sample with an explanatory note, an envelope, and a stamp during November 1995. In a case in which there was no response, two reminders were sent to the subject. In Estonia, two versions of the questionnaire were used, a Russian and an Estonian version. The Russian version was mailed to subjects with Russian names and the Estonian version to subjects with Estonian names. In cases in which the subject's language was uncertain, both versions were sent. The questionnaire included questions about respiratory symptoms and diseases, for example recurrent wheeze, attacks of shortness of breath, long-standing cough, sputum production, asthma, allergic rhinitis, chronic bronchitis and symptoms in special circumstances with varying exposures. The questionnaire also included questions about smoking habits, occupation, and family history of the above mentioned diseases. Two questions concerning exposure to ETS at home and outside the home were added in the Estonian study, exclusively, and were as follows. 1) "Does somebody of your family member smoke at home in living rooms?" This question was answered with either "yes" or "no/don't know", as were all questions concerning symptoms. 2) "How many hours per day do you spend in smoky rooms outside your home?" The reply had to be one of the following alternatives: ">5 h·day–1", "1–5 h·day–1", "<1 h·day–1", "nearly never", "I don't leave home".
Definitions
Exposure to ETS at home was defined as a positive answer to the first ETS question seen above. Exposure to ETS outside home was estimated by the answer to the second ETS question seen above. A never-smoker was defined as someone giving a negative reply ("no/don't know") to the two following questions: 1) "Do you smoke? (smokers also include those who smoke a few cigarettes or pipe fills a week, and those who have stopped during the last 12 months)"; and 2) "Have you been a smoker but have stopped smoking >1 yr ago?"
The following definitions of the dependent variables were used for respiratory symptoms or conditions. Long-standing cough: having had a long-standing cough during the last few years. Increased sputum production: often having phlegm when coughing or having difficulties in bringing up phlegm. Chronic productive cough: bringing up phlegm when coughing on most days during periods of 
3 months during at least 2 successive yrs. Wheeze: wheezing, whistling or a noisy sound in the chest when breathing. Wheezing during the last 12 months or having had wheezing or whistling in the chest at any time during the last 12 months. Woken with chest tightness or having woken with chest tightness at any time in the last 12 months. Dyspnoea grade 2: getting short of breath or having to walk more slowly when walking with other people of the same age on level ground at a normal pace. Physician-diagnosed chronic bronchitis: having been diagnosed as having chronic bronchitis or emphysema by a physician. Physician-diagnosed asthma: having been diagnosed as having asthma by a physician.
Lower airway irritant
The questionnaire also included the following nine questions concerning exposures and/or circumstances with the potential to cause lower airway irritation: "Do you become breathless or wheeze, or do you have attacks of cough when exposed to 1) exercise, 2) cold air, 3) exercise in cold air, 4) dust, 5) tobacco smoke, 6) car exhaust fumes, 7) strong smells, e.g. perfume, spices, printers ink, 8) pollen from plants and/or trees, or 9) pets?" If a positive response was given, the factor and/or circumstance were defined as a lower airway irritant. Odds ratios (ORs) for giving a positive response to questions concerning various lower airway irritants were calculated in relation to reported ETS-exposure duration. This was performed in an identical manner to the calculations of OR for respiratory symptoms (see Data analysis).
Data analysis
The analyses were based only on the participants who had never smoked. When estimating the effects of ETS exposure outside the home on respiratory symptoms, multiple logistic regression was used to calculate OR values with 95% confidence intervals (CIs), adjusted for age, sex, heredity for asthma and/or bronchitis/emphysema, community and ETS exposure at home. Males and females were analysed together, but an interaction between the subject factor sex and the within factor ETS exposure outside home was tested with a likelihood ratio test 18. This was obtained as minus twice the difference between log-likelihood for the models with and without the interaction term. Dose/response was also analysed in the same way with a likelihood ratio test, by comparing a linear ETS exposure effect coded from 1 to 4, where 1 was "nearly never" and 4 was ">5 h".
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Results |
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The demographical characteristics and exposure to ETS at home or work are shown in table 1
. Exposure at home was more common in females (31%) than in males (19%). In contrast, exposure outside the home was more common in males (53%) than in females (37%) and 23% of the males reported 1 h of ETS exposure outside of the home compared to 16% of females.
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), except for physician-diagnosed asthma, where only a slight increase was observed. The reported duration of ETS exposure was associated with positive responses for all types of lower airway irritants (table 3).
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All respiratory symptoms and conditions were more common in females than in males, except physician-diagnosed asthma, where the OR for females was 0.93 (0.62–1.39) (table 4). The female predominance was most clearly observed in dyspnoea grade 2 (OR 2.88 (2.13–3.90)), followed by increased sputum production (OR 1.67 (1.45–1.93)) and least pronounced physician-diagnosed chronic bronchitis (OR 1.29 (1.04–1.60)).
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). Dust was the most commonly reported lower airway irritant in males, followed by tobacco smoke. Females more frequently gave positive responses to all questions concerning lower airway irritants.
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Discussion |
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Lam et al. 11 did not show dose/response relationships between ETS exposure and respiratory symptoms as clearly in females as in males, but the present study did show females to be at least as sensitive as males to ETS exposure. The strengths of the present study are the sample size, the random selection from the general population and the high participation rate. Furthermore, the smoking prevalence in Estonia is high as 
50% of the males are smokers (data not presented). Almost no restrictions on ETS existed at the time of the study, giving a reasonable number of exposed subjects for calculations. A potential weakness of this study is the lack of validation regarding smoking status and ETS exposures. Smoking status was self-reported by the participants, which increased the risk of smokers being misclassified as nonsmokers. However, a meta-analysis 19 of the validity of self-reported smoking suggested a high sensitivity (87%) and specificity (89%) for self-report. Indeed, Riboli et al. 20 estimated that the proportion of females misreporting their active smoking habit was between 1.9–3.4% in 13 centres from 10 countries. If a misclassification of 3.5% is assumed, misclassification of smoking status does not explain the excess risks associated with ETS. Thus, possible misclassification cannot explain the strong ETS effects observed in both females and males. However, it is possible that some nonsmokers did not report ETS exposure even if they were exposed and, therefore, could have been misclassified as unexposed. A validation of outcome measures for respiratory symptoms was not performed, but these measures have been tested in several other studies and been found to have a high level of validity 21.
Another potential weakness is that the levels of ETS exposure were not directly measured. However, the self-reported ETS exposure can be accepted as a valid measure in the study as clear dose/response relationships were observed between the reported time with ETS exposure outside the home and most respiratory symptoms. The respondents were anonymous and would have found no advantages, real or expected, to giving falsified reports. The participants reported respiratory symptoms first and ETS exposure later in the questionnaire, which makes it less likely that reported respiratory symptoms would be biased by reported exposure to ETS. Subjects with asthma or chronic obstructive pulmonary disease might be more aware of ETS exposure, owing to an increased bronchial reactivity, and might therefore overestimate the length of exposure, leading to an overestimation of the risk 22. Alternativley, subjects with airway disorders like asthma might be more likely to avoid ETS and, if successful, will report less exposure, leading to an underestimation of the risk. This perhaps partly explains the lack of association between passive smoking at home and respiratory symptoms, i.e. family members may be more likely to stop or reduce smoking if one of their family members develops respiratory symptoms.
ETS exposure at home slightly increased ORs for some respiratory symptoms, but were not statistically significant. Lam et al. 11 concluded that "stronger effects were observed at work where the risk of ETS exposure was much greater because subjects spent more time among a larger number of smoking co-workers at work than at home". The present study did not separate ETS exposure at work from other sources of ETS exposure outside of the home. It seems reasonable, however, that ETS exposure outside of the home was mainly related to work, since most of the subjects were of working age. Therefore, this study supports the hypothesis that ETS exposures outside the domestic area have more serious effects than ETS exposure at home. A recent study 23 showed that the amount of metabolites in a tobacco smoke-specific carcinogen in urine was six times higher among females exposed to ETS at home than amongst nonexposed females. As studies concerning airway symptoms and ETS exposure imply that ETS exposure in the workplace is more harmful, a study of tobacco smoke-specific carcinogens in urine after ETS exposure at work is urgently required. There is also a lack of epidemiological data concerning workplace ETS exposures and lung cancer 24.
In Estonia the level of awareness about the effects of ETS is currently low and few workplaces have smoking restrictions or have banned smoking. In the present study, 20% of the subjects were exposed to ETS outside home for >1 h·day–1. This level of exposure was associated with a 50% higher prevalence of symptoms like phlegm, cough and dyspnoea. The present data indirectly supports many studies 9, 25, 26, indicating that ETS exposure is associated with small deficits in adult lung function.
Cigarette smoke was the most commonly reported cause of lower airway irritation in the present study and a previous Swedish study 28. The present authors also found a clear association between ETS exposure outside the home and airway symptoms from a variety of lower airway irritants. Most of these were known, unspecific airway irritants, e.g. cold air and strong-smelling scents. However, some were found to be rather surprising agents, commonly related to immunoglobulin (Ig)E-mediated allergies, e.g. pollen and animals with fur. From the present data it cannot be determined whether ETS exposure just triggers unspecific airway sensitivity or increases the risk of IgE-mediated allergy, which has been shown in active 28 but not passive smokers 9.
The high prevalence of chronic respiratory symptoms clearly represents a major public health problem. Exposure to ETS in society is preventable. Banning smoking in the workplace can significantly and rapidly improve the respiratory health of employees 29 and has also been reported to reduce the number of daily smokers and the number of cigarettes consumed in prevailing smokers. Implementation of stronger legislation in Estonia and all other countries with few regulations against ETS should be of high priority.
In summary, the reported duration of daily passive smoking outside of the home was associated with an increased prevalence of respiratory symptoms and a clear dose/response. This strongly supports the finding of a causal association.
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) and males (
).