Association of time–location patterns with urinary cotinine among asthmatic children under household environmental tobacco smoke exposure

• ETS is a major indoor pollutant, and is associated with severe asthma symptoms among children.
• The major source of ETS exposure for children is associated with the presence of adult smokers at home.
• Longer exposure hours to ETS at home is associated with higher urinary cotinine concentration.
• Public health promotion is changed to home-smoking restrictions being promoted.

IntroductionEnvironmental tobacco smoke (ETS) is a hazardous component of indoor air, and may increase the risk of respiratory diseases, atherosclerosis and otitis media in children. In this study, we explored the relationship between time inside the house, ETS exposure and urinary cotinine level, and also determined the association of time inside the house on asthma phenotypes when children exposed to ETS.MethodsA total of 222 asthmatic children and 205 non-asthmatic controls were recruited in the Genetic and Biomarker study for Childhood Asthma (GBCA). Structured questionnaires and time–location pattern questionnaires were administered by face-to-face interview. Urinary cotinine was measured by liquid chromatography tandem mass spectrometry (LC/MS/MS). The level of household ETS exposure was assessed using the cotinine/creatinine ratio (CCR).ResultsIn general, urinary cotinine and CCR were higher in subjects exposed to household ETS than those who never had ETS at home. A significant positive relationship was found between average time inside the house and urinary CCR in asthmatic children with current ETS at home (β=0.278, p=0.02). After adjustment for age and gender, average time inside the house was positively related to severe wheeze in asthmatic children with household ETS within 1 month (OR: 1.26, 95%: 1.02–1.64).ConclusionsOur study suggests that the major source of ETS exposure for children is due to longer period of exposures among children living with adult smokers at home. Home-smoking restrictions that effectively prevent children from being exposed to ETS would be worthwhile.