Effect of Smoking Habits of Family Adults on the Respiratory Health of Children in Southeastern, Iran

M. Janghorbani PhD, M. Shafiee-Bafti MD

Department of Community Medicine, School of Medicine, Kerman University of Medical Sciences, Kerman, Iran

Key Words · Passive smoking · tobacco · respiratory diseases · respiratory infections

Introduction

Tehere is increasing concern about the effects of the smoking habits of family adults on the health of infants and children.¹ Passive smoking (PS), a well recognized health hazard, is the most common indoor environmental pollution to which children are exposed.² Children, whose parents smoke, have an increased risk of contracting respiratory illness and developing symptoms including lower expiratory flow, wheezing, snoring, atopy, bronchitis, otitis media and respiratory infections, when compared to children of non-smokers.^3-13

While there have been substantial studies in developed countries, relatively little research has been undertaken in developing countries, where the problem is much greater. The risk of PS is also a serious problem in Iran. Infants and children are exposed to cigarette smoke both inside and outside the home. In order to support tobacco control policies, there is an urgent need for substantial evidence concerning the impact of PS on children's health in Iran.

This study, using household exposure to cigarette smoke as an estimate of PS, attempted to further clarify the effects of smoking of family adults on the respiratory health of infants and children during the first 4 years of life.

Subject and Methods

Subjects:

The study group comprised of infants and children with respiratory symptoms who were selected randomly from 6 pediatric clinics of teaching hospitals, and private pediatric clinics in the city of Kerman from July to December of 1997. A "case" was defined as any infant or child having respiratory symptoms or illness such as, pneumonia, common cold, otitis media, sore throat, rhinitis, asthma, sinusitis, and croup.

A total of 138 cases were eligible and all of the parents or close relatives were interviewed personally.

Two hundred and fifty-two controls were selected over the same time period. The controls were patients with no respiratory illness, selected from referrals to the same clinic as the study group or referrals to the Dermatology Clinic of Kerman University of Medical Sciences during the same calendar period and matched regarding their age and gender (± 5 months). Information on age, residential area, and diagnosis was obtained from the patients' files and the preliminary "eligible" patients were reconfirmed. The control group comprised patients with no respiratory illness or symptoms who had been referred for neurological diseases (3.6%), gastrointestinal problems (65.9%), urinary complaints (6%), dermatologic disorders (8.7%), and other non-respiratory illnesses (15.9%).

Methods:

Using a pre-set structured questionnaire, the parents or close relatives of cases and controls were interviewed in the clinics, by a trained interviewer. One of the investigators performed all the interviews of both the case group and control group after a clinic visit. The questionnaire included inquiries on demographic information, the indoor cigarette smoking habits of family members, average length and amount of passive smoke exposure per day at home, paternal and maternal levels of education, and maternal occupation (housewife or employee).

In this study, PS was defined as the indoor exposure of a child to the smoke of one or more cigarettes per day of any member of the family sharing the same accommodation as the child for 12 months or more. In this study smoking refers to "cigarette smoking", the use of the other tobacco products such as pipe, or cigars, cigarillo and snuff is not common among Iranians.

Statistical analysis:

Means and standard error (SE) of means were presented for describing variables with continuous distribution. Mean and proportion of characteristics of cases, controls, passive smokers and non-smokers were compared using t-test and chi-square test. The OR was used to estimate the ratio of risk of acquiring respiratory illnesses among "exposed" children to that of "unexposed" children. The 95% confidence interval (CI) for OR was calculated using Comfield's method. To examine contributions of passive smoking as well as to calculate an adjusted OR to respiratory illness, a stepwise multiple logistic regression analysis was performed after considering the children characteristics (gender, age) and family background (parental education levels, mother's occupation, answers to the questionnaire) as potential confounders (Table 1).¹⁴

Results

Differences in the distribution of several risk factors among 138 cases and 252 controls are shown in Table 1. Out of the 390 questionnaires, 15.4% were answered by the child's father, 80.8% by the mother and the remaining 3.8% by a guardian. These proportions were similar in both the case and control groups. The case group had a longer duration of exposure each day and were older than the control group . The educational level of the fathers in the control group was slightly lower than that of the case group (p<0.05). The groups were comparable in respect to their residential area in the city as well as, mother's occupation, gender, feeding method, and the number of cigarettes per day smoked by members of the household. The patients and controls were 1 to 48 months of age at the time of interview, with means (SE) of 21.6 (1.1) and 16.5 (0.8) months, respectively.

Table 2 presents the prevalence and distribution of sources of PS and the consequent risk of acquiring respiratory illness. Prevalence of PS at home was higher among the case group (52.9%) as compared to the control group (27.8%). Although fathers were the main contributing source of cigarette smoke for both the cases and controls, the contributing percentage from fathers for the case group was higher (50%) than that of the control group (21%). The difference in percentage of exposure to fathers smoking between the cases and controls (29%) was statistically significant (95% CI: 19.2-38.7; p<0.001). None of the mothers used tobacco in any form on a regular basis and only about 8.5% of children whose fathers never smoked were exposed at home.

Table 3 shows the characteristics of 390 children according to their adult family members cigarette smoking status. Passive smoking is quite common for infants and children and 36.7% of the studied subjects experienced passive smoke exposure. There were 122 (31%) children whose fathers smoked cigarettes. Slight statistical differences were observed for mother's educational status (p<0.05).

Table 4 shows the adjusted OR by multiple logistic regression analysis that includes gender, age, parental educational levels, mother's occupation (two categories: housewife, employee), answers to the questionnaire (three categories: father, mother, and guardian) in the model. According to the model, PS is a significant predictor for the respiratory health of infants and children (adjusted OR=1.72). Age and father's education level also contributes to the respiratory health independent of other risk factors.

The reported mean (SE) number of cigarettes per day that subjects were exposed to were 7.4 (0.8) for the case group and 3.0 (0.4) in the control group (p<0.001).

Table 6 shows the OR for respiratory illness by period and level of exposure. The OR for respiratory illness among infants and children whose family adults smoked <9, 10-19, and ³ 20 cigarettes per day as compared to infants and children of non-smokers were 2.0 (95% CI: 1.05-3.79), 2.3 (95% CI: 1.19-4.29), and 5.6 (95% CI: 2.88-10.87) respectively. (Mantel-Haenszel test for linear association=32.0, df=1, p<0.001). A similar pattern was observed when OR was calculated according to the period of exposure. The OR associated with 31-60 per/day was 2.4 (95% CI :1.25-4.72). For greater than 60 per/day, the OR was 5.3 (95% CI: 2.4-11.7) (Mantel Haenszel test for linear association=32.5, df=1, p<0.001). The reported mean (SE) number of minutes per day that subjects were exposed were 27.8 (3.3) for the case group and 11.0 (1.5) for the control group (p<0.001).

Discussion

In this study we found that passive smoking was significantly associated with respiratory illnesses among infants and children who lived with adult smokers. This finding is consistent with many other studies.^10,15-20 A possible explanation for this observation is the impairment of the defence mechanisms of the bronchial epithelium, such as mucocilliary clearance, by the exposure to pollution²¹ which results in increasing susceptibility to a variety of pathogens.²²

In our study, the father was usually the single most important contributing source of cigarette smoke and, from father or other family members, was taken as an estimate of PS. We did not find any mother who smoked regularly. This was consistent with our earlier study results obtained from 702 pregnant women and 600 female patients with coronary and non-coronary heart disease .^23,24 In assessing the effect of PS, infants and children, as the studied subjects, offer some advantages over adults²⁵ due to their relatively simple lifestyle. Household exposure to tobacco smoke may be the sole important source for infant and children, since they spend most of their time at home, and the potential effect of PS is not confounded by their own cigarette smoking and occupation. Moreover, infants and children might be more susceptible to the pollutants of cigarette smoke. However, in evaluating our findings some issues of validity are worth mentioning. Admittedly information bias is "inherit" in case-control studies. At present, information about exposure to PS is obtained from parents at interview. In this study, the interviewer was not blinded to the subject's case/control status. In an attempt to limit information bias, we used a structured questionnaire and standardized interview techniques, both of which are often helpful in minimizing interview bias. The main argument used to discredit the results of a study refers to the presence of serious biases in the study design, such as poor assessment of passive smoke exposure and lack of control for confounding variables. The criticism concerning exposure assessment are based on the poor reliability of the quantification of PS through the adult family member's smoking habits. On the other hand, the actual amount of passive exposure may be related not only to the exposure time, but also to the concentration of residual smoke in the room, and smoking behavior. Even though we attempted to control several confounders, it is difficult to avoid the potential confounding effect of indoor air pollution, urbanization, toxic component content of smoke, household ventilation, the volume of enclosed space, time spent indoors, etc.

In conclusion, passive smoking has deleterious effects on the respiratory health of infants and children and no confounding factors were found to be responsible for this association. From a public health point of view, health benefits for children can be achieved by systemic and parallel efforts to discourage parents from smoking. The evidence of adverse health effects of PS should be used to support stronger tobacco control measures and more relevant health warnings and health education messages.

Acknowledgements

We wish to thank Dr. Akbar Ahmadi for his co-operation in collecting data.

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