The evidence presented here is derived from a systematic review published by Jones (2011) that assessed the effect of exposure of infants to passive smoking on the incidence of lower respiratory infections (LRI) occurring in the first 2 years of life. An updated search for additional original studies was performed starting in 2011 up to February 2013. From these searches, a total of 34 studies were identified.
The outcomes assessed in the 34 included studies varied. Five studies assessed acute respiratory infection, eight studies assessed bronchitis and/or bronchiolitis, and in 21 studies the type of LRI was not specified.
Measurement of infant exposure to passive smoke was determined through self-report in 29 studies and by measuring levels of biochemical indicators of smoking in the body in five studies.
Eighteen of the included studies considered the effects of any household member smoking, six of both parents smoking, nine of paternal smoking, 16 of maternal smoking, and 11 of pre-natal maternal smoking (some studies covered more than one exposure).
Seventeen of the included studies were conducted in Europe.
The methodological quality of the 34 studies, as judged by the Newcastle-Ottawa scale score, gave an overall median score of 6 (range 4─8). Before the quality was evaluated, scores of <7 were designated as indicative of low quality and scores of ≥7 were designated acceptable as high quality. Therefore, 16 of the 34 studies were judged to be of high quality.
Publication bias was assessed visually using a funnel plot for the association between exposure to household passive smoke and the risk of LRI. There was no evidence of publication bias identified from this funnel plot.