Introduction

Passive smoke, also known as environmental tobacco smoke, comes from two sources: smoke breathed out by the person who smokes (also known as exhaled mainstream smoke), and smoke from the end of a burning cigarette (also known as sidestream smoke)¹. Exhaled mainstream and sidestream smoke both contain over four thousand chemicals; two hundred of which are poisonous and forty-three carcinogenic¹.

The United States Environmental Protection Agency (EPA) classify passive smoke as a Group A carcinogen. The Group A designation has been used by EPA for only fifteen other pollutants, including asbestos, radon and benzene¹. The excess risk of lung cancer in non-smokers who live with smokers as opposed to non-smokers is in the order of 26%².

Allowing for dietary factors, non-smokers living with smokers have an excess risk of developing ischaemic heart disease of 26%³. Glantz and Parmley⁴ stated that this risk translates into about 10 times as many deaths from environmental tobacco smoke induced heart disease as lung cancer and that this makes passive smoking the third leading preventable cause of death in the United States, behind active smoking and alcohol.

Passive smoke exposure is causally associated with additional episodes and increased severity of symptoms in children with asthma⁵. Symptoms of asthma are twice as common in the children of smokers⁵. Passive smoke is also causally associated with an increased risk of lower respiratory tract infections such as bronchitis and pneumonia and with an increased risk of otitis media, middle ear effusion and referral for glue ear, in the children of parents who smoke⁵.

Furthermore, the Confidential Enquiry into Stillbirths and Deaths in Infancy⁶ concluded that the number of sudden infant deaths could be reduced by almost two-thirds if parents did not smoke.

Previous studies have shown that questionnaires are a reliable marker of exposure to passive smoking⁷. Our study involved distributing a questionnaire to school children in order to establish the prevalence of passive smoking and to discern whether exposure to passive smoke takes place within or outside the home.

Methods

The questionnaire used in the study was based on that used by DellOrco et al in their Italian study⁸. This contained questions relating to sex, age pupils smoking habits, parental smoking habits, the smoking habits of other household members as well as questions regarding possible exposure to smoke outside the home. A final section contained questions regarding pupils attitude to passive smoke.

Sample size was calculated by computer using an estimated true proportion of passive smokers of 55%. For a confidence interval of 95% and a maximum acceptable difference of 0.075 (7.5%) the required sample size was 186. The number of people aged 12 to 17 inclusive in Sligo/Leitrim is 920312. Our questionnaire was distributed to a total of 265 pupils, the youngest being 12 and the oldest 17, in three secondary schools in the Sligo/Leitrim area of North West Ireland. These 3 schools were a sample of convenience, being the three secondary schools closest to the authors practice. The total number of pupils in the three schools was 1850. The questionnaires were distributed by systematic sampling of the school register to 1 in every 7 pupils. Three questionnaires were incomplete and rejected as unsuitable for analysis.

Coded data was entered on a spreadsheet using Microsoft Excel 4. SPSS 8 was used for data analysis.

Results

Smoking Status: Pupils and Parents

Of the 262 valid questionnaires, 188 pupils(72%) classified themselves as nonsmokers. Thirty-six(14%) were ex smokers and 37(14%) current smokers. Seven (19%) of the current smokers smoke less than one cigarette per day, whilst only 1(3%) admitted smoking more than twenty per day.

One hundred and forty-three subjects (55%) described their mothers as non-smokers, 45 (17%) as ex smokers and 65(25%) as current smokers. One hundred and twenty-nine subjects (49%) described their fathers as non-smokers, 64 (24%) as ex smokers and 61 (23%) as current smokers. Nineteen (7%) of the subjects had both a mother and a father who smoked.

Smoke in the home environment and in the wider community

One hundred and fifty-eight pupils (60%) described their home as not at all smoky over the previous 3 days, whilst 85(33%) described their home as at least a little smoky, the remaining 19(7%) being uncertain as to the amount of smoke.

One hundred and ninety-five pupils (74%) had been in a closed place with smokers, outside the home, within the previous 3 days (Table 1). Ninety-nine (51%) were exposed to passive smoke for at least 2 hours.

Thus 85(32%) pupils were exposed to smoke at home and 195(74%) pupils were exposed to smoke in the wider community, whilst 69(26%) pupils were exposed to smoke both at home and in the community. Two hundred and eleven pupils (81%) were therefore exposed to passive smoke at some location.

Attitude to passive smoke

Eighty-four students (32%) never found passive smoke annoying (Table 2). The remainder of the students found passive smoking annoying at least part of the time (110 (42%)) or all the time (65(25%)). Response rate to this question was 99%.

Non-smoking subjects were more likely to always find passive smoke annoying than ex smokers or current smokers (P=.001). They were also more likely to feel there should be more restrictions on the places in which people can smoke in public (P<.001 Chi-Square = 19.790 with 4 degrees of freedom). One hundred and seventy-eight pupils (70%) would like to see more restrictions on the places in which people can smoke in public, approximating the percentage that found passive smoke annoying.

Discussion

The prevalence of passive smoking found in the survey population, using indices such as reported smoke in the home or exposure to smoke outside the home was found to be 81% (211 subjects). This is higher than the prevalence of 53% found by Cook et al in their London based study⁶ and of DellOrco et al in Italy (65%)⁵. However the differences may have arisen because these studies excluded children who were active smokers. One limitation of our study is that the survey took place on a Monday, when recent exposure to passive smoke has been at its highest¹⁰.

Only 14% of pupils described themselves as current smokers, a lower finding than a recent government report, which showed that 21% of 9-17 year Olds in Ireland were smokers¹¹. Some smokers may have classed themselves as ex-smokers. In order to simplify the questionnaire no definition of ex-smoker (such as not having smoked within the previous month) was included. Such a definition may have led to a more accurate estimation of active smokers.

Questionnaires rely on subject recall and are therefore open to bias. Children may not be truthful answering questions with regard to their smoking status or that of their parents both because of peer pressure and because of possible repercussions from those they perceive to be in a position of authority. However when Williams et al¹²asked a group of white middle-class New York adolescents whether they smoked and then measured their serum cotinine level, only 2% were found to have replied untruthfully. In a similar study Jarvis et al¹⁰found that the level of deception in a group of UK school children was only 1%. The questionnaire used in this had been validated in previous research⁵, however, given the conflicting results of other studies it would be interesting to perform a further survey of passive smoking in Ireland and to validate it by means of cotinine assay.

Exposure to Smoke in the Home and in the Wider Community

Reported levels of smoke was used as a measure of passive smoke exposure in the home as parental smoking may not have included other smoking members of the household. Eighty-five pupils (32%) reported their home as smoky. In comparison to other studies this is a surprisingly low result. Cook found that 53% of 5-7 year old London children were exposed to smoke at home⁹, whilst 65% of Italian children were exposed to smoke at home in the study by DellOrco et al⁸. The data is consistent with the reported smoking habits of the subjects parents, so may simply indicate that parental smoking has a lower prevalence in Sligo/Leitrim than in London or Italy or that parents avoid smoking in the home.

In contrast 195 (74%) pupils stated that they had been exposed to smoke in a closed place outside the home within the previous 3 days, 99(51%) of them being exposed for more than 2 hours. Thus whilst the reported exposure at home may be lower than in other studies, there would appear to be an increase in exposure to smoke in the wider community.

This has important implications for possible methods of intervention, as simply targeting parents in a health promotion program may have only limited effect .One limitation of the questionnaire was that pupils were not asked to define where exactly they were exposed to smoke. It would be interesting to use a future study to ascertain the location of smoke exposure and the weekly lifestyle variations of the subjects.

Passive Smoke: What can be Done?

This study has shown that school children in Counties Sligo and Leitrim are exposed to passive smoke. Moreover they are exposed to smoke both at home and in the wider community. A significant proportion of pupils are also active smokers. Having quantified the problem, what can be done to reduce the incidence of active and passive smoking in this age group?

Given the significant adverse health effects caused by parental smoking, general practitioners should maintain a high index of suspicion and actively seek a smoking history from parents. This study has shown that children will admit both to their personal smoking habits and to their exposure to smoke at home and in public places. Whilst the ultimate objective must be parental smoking cessation, parents can at least reduce the effects of passive smoke by not smoking in the house, by increasing ventilation in the house, by not smoking in their car, by not smoking when children are present and by ensuring that others, such as baby-sitters do not smoke in the house or near their children.

Legislation exists to restrict smoking in public places. However, the law may not always be strictly enforced. Public attitudes may be tolerant of smoke at present, but the situation is changing; as demonstrated by the pupils attitude to restrictions on smoking.

There have recently been a number of high profile civil actions taken against employers such as airlines who allowed their workers to be exposed to smoke in their work place. Fear of litigation may force many businesses to restrict or ban smoking on their premises.

Finally, people should avail of no-smoking areas in public places, should encourage proprietors of restaurants and bars to consider their non-smoking clientele and should encourage their political representatives to take further action to reduce the dangers of passive smoke.

Correspondence:

David Swann,
Department of Public Health,
North Western Health Board,
Bishop Street,
Ballyshannon,
Co. Donegal.
Tel: +353-72-52900
Fax: +353-72-52901.

References

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