Association of indoor nitrogen dioxide exposure with respiratory symptoms in children with asthma

Rationale: Chronic exposure to indoor nitrogen dioxide (NO2) is a public health concern. Over half of U.S. households have a source of NO2, and experimental data suggest potential for adverse respiratory effects. Objective: To examine associations of indoor NO2 exposure with respiratory symptoms among children with asthma. Methods: NO2 was measured using Palmes tubes, and respiratory symptoms in the month before sampling were collected during home interviews of mothers of 728 children with active asthma. All were younger than 12 yr, lived at the sampled home for at least 2 mo, and had asthma symptoms or used maintenance medication within the previous year. Measurements: Respiratory symptoms (wheeze, persistent cough, shortness of breath, chest tightness). Results: Mean (SD) NO2 was 8.6 (9.1) ppb in homes with electric ranges and 25.9 (18.1) ppb in homes with gas stoves. In models stratified by housing type (a factor associated with socioeconomic status), gas stove presence and elevated NO2 were each significantly associated with respiratory symptoms, controlling for age, ethnicity, medication, mold/mildew, water leaks, and season of sampling. Among children in multifamily housing, exposure to gas stoves increased likelihood of wheeze (odds ratio [OR], 2.27; 95% confidence interval [95% Cl], 1.15, 4.47), shortness of breath (OR, 2.33; 95% Cl, 1.12, 5.06), and chest tightness (OR, 4.34; 95% Cl, 1.76, 10.69), whereas each 20-ppb increase in NO2 increased both likelihood of any wheeze (OR, 1.52; 95% Cl, 1.04, 2.21) or chest tightness (OR, 1.61; 95% Cl, 1.04, 2.49), and days of wheeze (rate ratio (RR), 1.33; 95% Cl, 1.05, 1.68) or chest tightness (RR, 1.51; 95% Cl, 1.18, 1.91). Conclusion: Exposure to indoor NO2 at levels well below the Environmental Protection Agency outdoor standard (53 ppb) is associated with respiratory symptoms among children with asthma in multifamily housing.