Effect of Interaction Between Tobacco Smoke and Particulate Matter on Childhood Airway Hyperresponsiveness

Rationale: Particulate matter and tobacco smoke exposure affect respiratory health, such as, respiratory tract infections, wheezing, asthma and decreased lung function. Studies about their interaction, especially development of airway hyperresponsiveness (AHR), were limited. To investigate whether outdoor particulate matter (PM₁₀) and tobacco smoke exposure increase the risk of AHR.

Methods: From 2005, 2,168 elementary school children were enrolled to a prospective 4-year follow-up survey. Individual exposure to PM₁₀ was estimated by using a geometric information system from birth to 2004. Measuring urine cotinine levels and methacholine challenge test were conducted every 2 years from 2005.

Results: PM₁₀ from birth to 2004 and urine cotinine at start year increase the risk of AHR at start year (aOR 1.48, 95% CI 1.18-1.87 and aOR 1.48, 95% CI 0.99-2.21, respectively). PM₁₀ for 2years before start year and urine cotinine at start year increased the risk of AHR at start year additively (aOR 1.95, 95% CI 1.08-3.50, p for interaction 0.117). Higher urine cotinine levels during 4-year follow-up increased the risk of new AHR (positive conversion from PC20 > 16mg/dl) in children with higher PM₁₀ from birth to 2004 (aOR 2.66, 95% CI 1.10-6.45, p for interaction 0.005). However, cotinine at start year/ PM₁₀ from birth to 2004 and cotinine during 4- year follow-up period/ PM₁₀ for 2years before start year did not increase the risk of new AHR.

Conclusions: Short-term exposures to PM₁₀ and/or tobacco smoke increase the risk of AHR additively. Long-term combined exposure is more important in new development of AHR.