Health effects of indoor nitrogen dioxide and passive smoking on urban asthmatic children

Background: Nitrogen dioxide (NO₂) and environmental tobacco smoke (ETS) have been associated with adverse respiratory effects. Objective: We sought to assess the effect of NO₂ and ETS on asthma morbidity among children in inner-city environments. Methods: Asthmatic children between the ages of 4 and 9 years had exposure to NO₂ and ETS measured by using Palmes tubes in the home and urinary cotinine. A baseline interview and telephone assessments at 3, 6, and 9 months evaluated health service use, asthma symptoms, and peak flow rates. Results: Gas stoves were present in 87.8% of 469 homes. The median level of indoor NO₂ was 29.8 ppb compared with the US national outdoor median of 18 ppb. Of 1444 children, 48% had urinary cotinine/creatinine ratios of greater than 30 ng/mg. The median level of the cotinine/creatinine ratio was 42.4 ng/mg in smoking homes compared with 18.0 ng/mg in nonsmoking homes. The relative risk for asthma symptoms with increased NO₂ exposure was 1.75 (95% CI, 1.10-2.78) in children who did not have positive skin test responses. Higher NO₂ exposure resulted in lower peak flows during colder months (relative risk, 1.46; 95% CI, 1.07-1.97). Higher ETS exposure in colder months was weakly associated with lower peak flows (relative risk, 1.21; 95% CI, 0.99-1.47). There was no effect of ETS exposure on symptoms or use of health care services. Conclusion: Higher levels of indoor NO₂ are associated with increased asthma symptoms in nonatopic children and decreased peak flows. Clinical implications: Interventions to reduce NO₂ exposure, such as venting of gas stoves, might help reduce asthma morbidity.