Magnitude and Chronicity of Environmental Smoke Exposure Across Infancy and Early Childhood in a Sample of Low-Income Children

Introduction: Infants and young children may be at an increased risk for second- and thirdhand exposure to tobacco smoke because of increased respiration rate and exposure to surface residue. However, relatively fewer studies have examined biomarkers of exposure (cotinine) in children under age 4 years. This study examines the magnitude and chronicity of exposure across early childhood among children from low-income families in order to better characterize contextual risk factors associated with exposure.

Methods: A total of 1292 families were recruited in six nonurban counties of Pennsylvania and North Carolina. Cotinine was assayed from infant saliva at 6, 15, 24, and 48 months of age (N = 1218), and categorized as low (≤0.45 ng/mL), moderate (0.46-12 ng/mL), or high (≥12 ng/mL) at each time point. Categories were highly correlated across time. Latent class analysis was used to summarize patterns of exposure categories across time.

Results: Magnitude of exposure in this sample was high, with approximately 12% of infants registering cotinine values at least 12 ng/mL, consistent with active smoking in adults. Greater exposure was associated with lower income, less education, more residential instability, and more instability in adult occupants in the home, whereas time spent in center-based day care was associated with lower exposure.

Conclusions: Young children from low-income, nonurban communities appear to bear a higher burden of secondhand smoke exposure than previous studies have reported. Results contribute to understanding populations at greater risk, as well as specific, potentially malleable, environmental factors that may be examined as direct contributors to exposure.

Implications: Results suggest that infants from low-income, nonurban families have higher risk for environmental smoke exposure than data from nationally representative samples. Predictors of exposure offer insights into specific factors that may be targeted for risk reduction efforts, specifically conditions of children's physical space. In addition to considering the increases in risk when an adult smoker lives in a child's home, families should also attend to the possible risk embedded within the home itself, such as residual smoke from previous occupants. For high-risk children, day care appears to mitigate the magnitude of exposure by providing extended time in a smoke-free environment.