Objective: To measure the effect of environmental tobacco smoke (ETS) on respiratory health in a national sample of young children.
Methods: The study evaluated children 2 months through 5 years of age participating in the Third National Health and Nutrition Examination Survey, 1988 to 1994. The group was a representative sample of the US population (N = 7680). A parental report of household smoking or maternal smoking during pregnancy ascertained ETS exposure. Respiratory outcomes were based on parental report of wheezing, cough, upper respiratory infection, or pneumonia in the last 12 months and chronic bronchitis or physician-diagnosed asthma at any time. Logistic regression was used to adjust for age, sex, race/ethnicity, birth weight, day care, family history of allergy, breastfeeding, education level of head of household, and household size.
Results: Approximately 38% of children were presently exposed to ETS in the home, whereas 23.8% were exposed by maternal smoking during pregnancy. ETS exposure increased chronic bronchitis and three or more episodes of wheezing among children 2 months to 2 years old and asthma among children 2 months to 5 years old. For household exposure, a consistent effect was seen only at >/=20 cigarettes smoked per day. Adjusted odds ratios for increased risk (95% confidence interval) for household exposures (>/=20 cigarettes smoked per day vs none smoked) and maternal prenatal exposure (prenatal smoking vs no smoking), respectively, for children 2 months to 2 years old were chronic bronchitis, 2.5 (1.6, 4.1); 2.2, (1.6, 3); three or more episodes of wheezing, 2.7 (1.7, 4.2), 2.1 (1. 5, 2.9); and for children 2 months to 5 years old were asthma, 2.1 (1.4, 3.2); 1.8 (1.3, 2.6). Reported use within the past month of prescription medications for asthma (beta-agonists or inhaled steroids) was not different between those with asthma reporting ETS exposure and those reporting no exposure; percent of patients with asthma reporting use of medication by household exposure was 0, 25. 7%; 1 to 19 cigarettes smoked per day, 32.9%; and >/=20 cigarettes smoked per day, 23.1%; percent of patients with asthma reporting use of medication by maternal smoking during pregnancy was no, 28.9%; yes, 22.7%. Among children 2 months to 2 years of age exposed to ETS, 40% to 60% of the cases of asthma, chronic bronchitis, and three or more episodes of wheezing were attributable to ETS exposure. For diagnosed asthma among children 2 months through 5 years old, there were 133 800 to 161 600 excess cases. Among exposed children 2 months through 2 years of age, there were 61 000 to 79 200 excess cases of chronic bronchitis and 126 700 to 172 000 excess cases of three or more episodes of wheezing.
Conclusions: ETS exposure is common among children in the United States. The reported prevalence of asthma, wheezing, and chronic bronchitis was increased with ETS exposures. No statistically significant increase in the prevalence of upper respiratory infection, pneumonia, or cough was associated with ETS exposure. ETS exposure has little effect on the respiratory health of children between 3 and 5 years of age, with the exception of asthma. ETS appears to increase the prevalence of asthma rather than the severity as measured by medication use. These findings reinforce the need to reduce the exposure of young children to ETS.