2.4 Statistical analysis
In total, 1107 Flu-p patients were identified and enrolled in this
study. These patients were then randomly assigned to derivation and
validation cohorts (80% and 20% of patients, respectively), which were
respectively used to develop and validate our prognostic model.
In addition, these 1107 patients were separated into two groups based
upon whether or not they underwent IMV within 14 days following
admission. Baseline characteristics were then compared between these two
patient groups, and all variables which yielded a P < 0.1 in
these initial univariate analyses were incorporated into a multivariate
stepwise logistic regression model to identify risk factors associated
with 14-day IMV rates. To ensure model simplicity, each risk factor was
assigned an integer score value associated with its corresponding
regression coefficient (β) value. Model cutoff scores were then defined
using receiver operating characteristic (ROC) curves based upon Youden’s
index. Kaplan-Meier analyses were conducted to compare rates of IV
between patients above and below this cutoff score (high-risk and
low-risk, respectively). The area under the ROC curve (AUROC) was used
to gauge the prognostic performance of this model based upon overall
sensitivity and specificity values.
A Kolmogorov–Smirnov test was used to assess result normality, with
normally and non-normally distributed variables being presented as means
± standard deviation and medians, respectively. Continuous variables
were evaluated with Mann-Whitney U tests or Student’s t-tests,
whereas categorical variables were assessed with Fisher’s exact test or
chi-squared tests. A two-tailed P < 0.05 was indicative of
significance. SPSS 22.0 or MedCalc 19.0 were used for all statistical
testing.
Results3.1 Patient screening
A total of 3405 hospitalized patients who were found to be positive for
influenza viral RNA during the study period were screened for
eligibility, of whom 1107 with laboratory-confirmed Flu-p were enrolled
in this study. Flu-p was associated with influenza A virus and influenza
B virus infections in 683 and 424 of these patients, respectively (
Figure 1).