PURPOSE OF THE STUDY.
This study aimed to examine the effects of airborne endotoxin on persistent asthma in an urban population by evaluating whether indoor pollutant exposure modifies the relationship between indoor airborne endotoxin and asthma morbidity.
One hundred forty-six urban Baltimore children and adolescents, aged 5 to 17 years, with persistent asthma were followed up for 1 year. Median age of participants was 11 years, 57% were male, and >90% were African American. The majority of participants were of low socioeconomic status.
Participants underwent clinical assessments at 0, 3, 6, 9, and 12 months. Skin prick testing for 14 allergens and total immunoglobulin E levels were obtained at the baseline visit. Spirometry and fractional exhaled nitric oxide measurements were performed at all study visits, as well as medical questionnaires. Airborne nicotine, endotoxin, and nitrogen dioxide (NO2) levels were measured at home visits. The effects of pollutant exposures on the association between endotoxin exposure and asthma outcomes were assessed via stratified and interaction analyses.
Both air nicotine and NO2 levels modified the relationship between home endotoxin exposure and asthma outcomes. For children with no exposure to nicotine at home, higher endotoxin exposure was associated with fewer acute visits and oral corticosteroid bursts. In contrast, for children in whose homes nicotine was detected, endotoxin exposure was associated with higher rates of acute asthma visits and oral corticosteroid bursts. Higher endotoxin level was positively associated with acute asthma visits for children living in homes with lower NO2 levels (<20 ppb). Fewer acute asthma visits were noted for children living in homes with higher NO2 levels. A similar interaction between endotoxin exposure and NO2 was also noted for asthma-related symptoms.
This study demonstrates that, for urban children with asthma, the effect of endotoxin exposure on disease morbidity is influenced by levels of exposure to indoor nicotine and NO2. Airborne endotoxin seems to be protective against acute asthma visits and oral corticosteroid bursts in the setting of very low or no air nicotine exposure, whereas it is associated with worse asthma morbidity in the setting of high indoor air nicotine exposure. In contrast, airborne endotoxin is associated with increased asthma morbidity in the setting of low NO2 exposure and seems to be protective against asthma-related morbidity in the setting of high NO2 exposure.
This study strengthens the idea that multiple components of the air we breathe can have complementing and/or opposing effects on asthma morbidity. This study reiterates the concept that airway hyperreactivity is multifactorial. Due to the high prevalence of concomitant indoor endotoxin exposure and secondhand smoke exposure, the association noted between airborne nicotine and endotoxin exposure may help explain the disproportionate asthma-related morbidity observed in urban populations. The findings support the importance of the interplay of indoor exposures and their effects on asthma. Effective approaches to environmental control, including smoking cessation or home smoking bans, may mitigate the harmful effects of endotoxin on asthma. Further studies are needed to support these conclusions.
- Copyright © 2014 by the American Academy of Pediatrics