School Endotoxin Exposure and Asthma Morbidity in Inner-city Children.

Background: Endotoxin exposure is associated with airway inflammation. Children spend 6 to 8 h/d in school, yet the effect of school-specific endotoxin exposure on asthma morbidity is not well understood.
Methods: In this longitudinal cohort study, 248 students with asthma, from 38 inner-city schools, underwent baseline phenotyping and follow-up. Clinical outcomes were evaluated throughout the academic school year and linked to classroom-specific dust and air endotoxin levels as well as home dust endotoxin levels. The primary outcome was maximum asthma symptom-days per 2-week period.
Results: Classrooms had higher settled dust endotoxin levels compared with homes (14.3 endotoxin unit/mg vs 11.3 endotoxin unit/mg; P = .02). Airborne endotoxin levels exceeding recommended occupational exposure limits for adults were recorded in 22.0% of classrooms. Classroom air endotoxin levels were independently associated with increased maximum symptom-days in children with nonatopic asthma, but not in those with atopic asthma (interaction P = .03). Adjusting for home exposures, classroom endotoxin exposure was independently associated with a dose-dependent increase in asthma symptom-days for children with nonatopic asthma (adjusted incidence rate ratio, 1.16 [95% CI, 1.03-1.31]; P = .02). In these subjects, maximum symptom-days increased by 1.3 days for each 14-day period when comparing students in classrooms with the lowest endotoxin levels compared with average measured levels.
Conclusions: Inner-city children with asthma are exposed to high levels of airborne endotoxin at school, resulting in increased asthma symptoms in children with nonatopic asthma. Mitigation of school-related exposures may represent a strategy to decrease asthma morbidity in this population.
Trial Registry: ClinicalTrials.gov; No.: NCT01756391; URL: www.clinicaltrials.gov.