Quantitative variables are described as means ± standard deviations or median and interquartile range (IQR), as appropriate. Qualitative variables are presented as absolute counts and relative percentages. χ2-test or Fisher’s exact test were used to compare proportions, as appropriate. For continuous variables, the 2-sample independent t-test or the Mann-Whitney-U-test were used. P-values ≤0.05 (2-sided) were considered statistically significant. Multivariate logistic regression was used to examine whether different predictors were associated with virus detection. Variables with a p-value ≤0.05 in the univariate logistic regression were included. SPSS version 20.0 for Windows software, OpenEpi (www.openepi.com) and Microsoft Excel 2010 were used for statistical analyses.