Statistical Analysis
Continuous variables were described using medians and interquartile
ranges (IQR). Categorical variables were described using counts and
percentages. Patient characteristics and outcomes were stratified by
primary exposure and compared using Chi-square or Fisher’s exact test
for categorical variables and Wilcoxon rank sum test for continuous
variables.
To examine the independent association between diagnosis of ARI or bARI
and isolation of any organism on respiratory cultures, as well as
specific isolation of P. aeruginosa and S. aureusisolation (the two most frequently isolated organisms), generalized
estimating equations were used including potential confounders while
accounting for within-patient clustering. Patient demographics included
age at culture collection, time with tracheostomy at culture collection,
race, ethnicity, and insurance type; measures of clinical complexity
included number of complex chronic conditions, BPD or CLDI diagnoses,
and baseline ventilator use; clinical variables included respiratory
culture source, as well as location and department sending specimen.
To examine the independent association between diagnosis of ARI and all
specific organism isolations simultaneously, a multinomial logistic
regression equation was calculated including the above potential
confounders, accounting for within-patient clustering, and additionally
accounting for culture-level clustering among polymicrobial culture
results.
To evaluate the test characteristics of the respiratory culture,
sensitivity, specificity, negative predictive value (NPV) and positive
predictive value (PPV) were calculated using clinician-coded diagnosis
of bARI as the reference standard and indicator of true bacterial
disease. Test characteristics were calculated for the respiratory
culture overall and by specimen type (i.e., TA, BAL).
Secondary analyses were conducted examining results of each respiratory
culture source (TA and BAL) individually. As isolation of P.
aeruginosa in both predictor groups may signal these children have
chronic colonization, subgroup analysis was conducted examining children
with chronic P. aeruginosa isolation. Additional subgroup
analysis excluding presumed surveillance BAL cultures without diagnosis
data was also conducted.
All analyses were performed with R v4.1.1 (Vienna,
Austria).16 P -values <0.05 were
considered statistically significant. This study was approved by the
CCHMC Institutional Review Board.