2.2 Analysis
Our analysis was performed with R version 4.02 and used the same
approach as our previously published analysis examining the performance
of RIDT in a clinical setting.10 Binomial logistic
regression models were used for adjusted associations. Adjusted models
were fit for predicting improvements in sensitivity and specificity
based on age, gender, number of days from symptom onset, presence and
absence of individual signs and symptoms (chills, cough, sore throat,
malaise, myalgia, runny nose, nasal congestion, headache), presence of
an influenza-like illness (ILI), illness severity (mild, moderate, or
severe), influenza vaccination status, co-detection of other pathogens,
and season (early, peak, or late). Specimens meeting inclusion criteria
that had missing information were included in the overall sensitivity
and specificity estimates, but they were removed from the adjusted
model. We defined ILI as having a fever with cough and/or sore throat
[23]. A quadratic term for age was not included because it did not
significantly improve the model (LRT p = 0.46). Interaction terms
between age and days from onset were also considered but ultimately
excluded due to lack of significance (LRT p = 0.11). Some students had
multiple specimens present in the dataset. Specimens, even from the same
student, were assumed to be independent for testing and modelling.
RESULTS
Of the 2,378 total student ARI episodes between January 5, 2015 and
March 12, 2020, 2,368 (99.6%) were included in this analysis. Nine
specimens (0.38%) were excluded from the overall analysis because the
child’s symptoms began more than seven days before the samples were
collected, and one (0.04%) was excluded because an RIDT was not
performed. For the adjusted model, 17 records were excluded because they
were missing severity of illness (n=12; 0.50%) or were marked as
missing the number of days from symptom onset due of an invalid test
date (n=5; 0.21%). Three (0.13%) specimens had inconclusive Sofia test
results. These were imputed as false positives in specificity analysis
as all three had negative PCR results.