2.4-Statistical analysis
Data were presented as median (interquartile ranges [IQR]) or number
(%). The categorical variables were compared between groups using the
χ2 or Fisher Exact test. The differences in the median of the continuous
variables were tested with the 2–sided Mann–Whitney or Kruskal–Wallis
test. With a priori adjustment for age (categoric variables), binary
logistic regression was used to predict the relationship between viral
coinfection and severe LRTI. Age was entered separately into the model
as a continuous and categorical variable and categorized as 1-3 months,
4-6 months, 7-12 months, 13-24 months, and 25-60 months (reference
level). In the table, potential risks were presented by using
categorized age. As a binary dependent variable, we assessed the
severity of the disease according to the site of the hospital stay: the
ICU (severe LRTI) or the short-term unit (mild LRTI). The predictors
associated with the dependent variable on univariate analyses (P< .05) were included in the model. As independent variables,
the weight-for-height SDS, history of atopy, exposure to tobacco smoke,
underlying conditions (categorized as; healthy [reference level],
CLD, CHD, NMD, IS, and previous history of LRTI), neutrophil
(categorized as; normal range [reference level], neutropenia, and
neutrophilia) and lymphocyte (categorized as; normal range [reference
level], lymphopenia, and lymphocytosis) status, and CRP value were
included. Also, dummy variables to represent each level of qualitative
independent variables included in the regression equation. First, virus
infection type in the model was categorized as; i) single virus
infection (reference level); ii) viral coinfection; iii) no-virus
infection. Secondly, subgroup analyses by each of the viruses were
performed to detect whether a specific virus coinfection led to severe
LRTI than this specific-virus infection alone. The 13 models of
comparing single and coinfection for each of the viruses were
categorized as; i) specific-virus single infection (reference level);
ii) specific virus and any virus coinfection; iii) single infections not
including this specific virus; iv) coinfections not including this
specific virus; v) no-virus infection. Finally, we conducted subgroup
analyses by age for viral coinfections. The Hosmer-Lemeshow test was
used to assess the goodness of fit for the model. Results were expressed
as odds ratios (ORs) with 95% confidence intervals (CIs), and P< .05 was considered statistically significant. Statistical
analyses were performed using the statistical program package SPSS
(Version 22.0; IBM Corp., Armonk, NY).