Statistical Analysis
Baseline demographics, clinical characteristics, and medication use were compared between the TA-B-BAL and control group using unpaired t-tests for continuous variables and Chi-square tests for categorical variables. Differences in the number of exacerbations, oral corticosteroid courses and emergency department visits between the TA-B-BAL and control group were examined by generalized linear mixed effects models (GLMM) with a Poisson distribution function. Changes in TRACK scores between the worst pre-visit and best post-procedure visit were evaluated by a paired t-test within each group.
In all regression models, fixed factors included patient group (TA-B-BAL vs control) and the event (pre-procedure vs post-procedure), as well as their interaction. The within-subjects’ correlation between pre-procedure and post-procedure measures was included by modeling random intercepts by patient.
Statistical analysis was performed using R 3.6.0 23and the “lme4” package 24.
Results
Between 2012 and 2019, 18 preschool patients (TA-B-BAL) were identified using the inclusion criteria. An additional 18 preschool patients (controls) with severe asthma who attended the asthma clinic during the same time period and did not undergo a TA-B-BAL procedure were identified. The TA-B-BAL and control patients were matched based on age, sex and follow-up time period. The baseline clinical features, comorbidities and demographics of all subjects are summarized inTable 1 . There were no statistically significant differences between the TA-B-BAL and control group except for anaphylactic food allergy.
The mean (SD) time elapsed between the pre-operative visit and the TA-B-BAL procedure was 3.61± 5.9 months. Seventeen (94%) of the cases returned to the asthma clinic for a post-procedure assessment within a mean time of 2.86±1.7 months after the TA-B-BAL, and 7.22±6.06 after the pre-operative visit. A second follow up assessment occurred for 11 (61%) of the cases 4.3±4.7 months after the post-operative visit and 6.9±4.8 months after the TA-B-BAL.
The virology and microbiology findings derived from the B and BAL are presented in Figure 2 . Cell counts were also performed revealing neutrophilia in 5 patients (>15%) and eosinophilia in 2 patients (>3%).