[Passive smoking respiratory risk. A quantitative synthesis of the literature]

Fifty nine scientific papers had been published in english or french literature, by 1988, on the matter of respiratory health effects of environmental tobacco smoke exposure (ETS). Fifteen dealt with lung cancer. An original meta-analytical approach was used in order to assess the consistency of these results, where the quality of the papers contributes to the weighing scheme, along with the traditional precision parameters. Lung cancer studies converge towards a point estimate of the relative risk (RR) near 1.5, contrasting non smokers exposed during a long time to ETS (mostly at home) and non exposed non smokers (95% confidence interval = 1.3-1.6). Important methodological difficulties did not allow, to date, to show consistent dose-effect relationship with duration or intensity of exposure. Chronic infections of lower respiratory tract related to ETS have been frequently observed (RR = 1.3; 1.2-1.4) as well among adults as among children. Wheezing and asthma are likewise more frequent among children exposed to ETS at home (RR = 1.2; 1.1-1.4). A modest, although statistically significant decrease of Forced Expiratory Volume at One Second is associated with passive smoking among children (mean effect = -0.5%). Health risk related to passive smoking are much lower than those caused by active smoking. However, this hazard should not be underlooked, since ETS is universally present in everyday life and since anyone may be exposed, including children, the elderly and those who suffer from chronic respiratory diseases. Many research needs are underscored by this meta-analysis. It remains that the current state of knowledge on health risks associated with passive smoking warrants that strong preventive action, educative or statutory, be promoted.