Statistical analysis
Continuous
variables were expressed as medians and interquartile ranges (IQR), and
categorical variables were presented as numbers and frequencies with
percentages to describe the
populations,
as appropriate. The two-group comparison was done by the Mann-Whitney-U
test, and Kruskal-Wallis H
nonparametric test was used for multiple comparisons between different
groups.
A
χ2 test or Fisher exact test was used to compare
categorical variables, as appropriate. Actuarial survival rates were
analyzed by the Kaplan-Meier method and survival was measured in days
from diagnosis to death or the last review. The log-rank test was
applied for comparisons between groups. Univariate and multivariate
logistic regression was performed to explore the association of clinical
characteristics and laboratory parameters and the risk for
superinfection. A stepwise backward conditional method was used to
select variables entering the multivariate model. Strongly correlated
variables were excluded from multivariate analyses. Multi-collinearity
was checked before determining the final model. We assessed goodness of
fit with the Hosmer-Lemeshow (HL) test. Data analysis was performed with
MedCalc and SPSS 24.0 for Windows software (SPSS Inc. Chicago). For all
tests, a two-sided P < 0.05 was considered as statistically
significant.