Second-Hand Tobacco Smoke and Allergens – Double Jeopardy for Childhood Asthma Exacerbations

Abstract

In this issue of Respiration, Dong et al. [4] report findings from a large cohort of 8,819 children (mean age = 4.7 years) sampled randomly from households based in 25 districts of Northeast China. They looked at different forms of respiratory symptoms: from persistent phlegm to current asthma, and from wheeze to doctor-diagnosed asthma both independently and then combined in the presence of childhood allergen and SHS exposure. The findings suggest that current exposure (allergen/SHS) had little or no effect on most of the respiratory symptoms studied. In contrast, in utero and post-natal ( 2 years) allergen/SHS exposures were significant risk factors. However, in the presence of allergens, current SHS exposure showed a significant increased risk of doctordiagnosed asthma although such modified effects were greatest when children had either in utero or post-natal SHS exposures. The present cross-sectional study has both strengths and limitations. Given the complexities of diagnosing childhood asthma and self-reported asthma and asthmalike symptoms, Dong et al. [4] took advantage of a large cohort to report such an association. To the best of our knowledge, no similar studies utilizing such a large cohort of children have yet been reported from any western country. Self-reported data could introduce both misclasAsthma is increasingly being considered a syndrome complex. The mechanistic pathway of asthma is still under exploration. Epidemiological studies, with all their inherent limitations, may provide important insights into causal relationships of a disease. The 2006 US Surgeon General’s Report had inferred a causal relationship of asthma and second-hand tobacco smoke (SHS) exposure [1] . There is no safe free level of SHS, which is also classified as a group 1 carcinogen [2] . Four thousand toxic chemicals constitute tobacco smoke. Steady increases in regional and national smoke-free policies are noted, especially in western societies. But the most vulnerable in society, the children, are silently and involuntarily being exposed to this deadly poison of tobacco smoke. The two most common settings in western society where children are exposed to SHS are in their homes or while travelling by private motor vehicles. The recent UK Royal College of Physicians (RCP) report indicated a 2-fold increased risk of childhood asthma with SHS exposure at home based on meta-analyses of 70 studies [3] . The estimates of childhood asthma vary depending on the type of SHS exposure: in utero or post-natal. Information on acute exacerbations of childhood asthma attributed to SHS (in utero/post-natal) in the presence of childhood exposure to allergens is, however, limited. Published online: December 30, 2010