Indoor pollutant exposures modify the effect of airborne endotoxin on asthma in urban children

Rationale: The effect of endotoxin on asthma morbidity in urban populations is unclear. Objectives: To determine if indoor pollutant exposure modifies the relationshipsbetweenindoor airborne endotoxinandasthmahealth and morbidity. Methods: One hundred forty-six children and adolescents with persistent asthma underwent repeated clinical assessments at 0, 3, 6, 9, and 12 months. Home visits were conducted at the same time points for assessmentof airborne nicotine, endotoxin,andnitrogen dioxide (NO₂) concentrations. The effect of concomitant pollutant exposure on relationships between endotoxin and asthma outcomes were examined in stratified analyses and statistical models with interaction terms. Measurements and Main Results: Both air nicotine and NO ₂ concentrations modified the relationships between airborne endotoxin and asthma outcomes. Among children living in homes with no detectable air nicotine, higher endotoxin was inversely associated with acute visits and oral corticosteroid bursts, whereas among those in homes with detectable air nicotine, endotoxin was positively associated with these outcomes (interaction P value = 0.004 and 0.07, respectively). Among children living in homes with lower NO₂ concentrations (>20 ppb), higher endotoxin was positively associated with acute visits, whereas among those living in homes with higher NO₂ concentrations, endotoxinwasnegatively associated with acute visit (interaction P value = 0.05). NO₂ also modified the effect of endotoxin on asthma symptom outcomes in a similar manner. Conclusions: The effects of household airborne endotoxin exposure on asthma are modified by coexposure to air nicotine and NO₂, and these pollutants have opposite effects on the relationships between endotoxin and asthma-related outcomes.