We performed statistical analysis using SAS version 9.1 (SAS Institute Inc., Cary, NC, USA). We calculated descriptive statistics for all study variables. We report continuous variables as medians with interquartile range (IQR) and categorical variables as percentages with 95% confidence interval (95% CI) where appropriate. We estimated age-based population admission rates [7, 11] . We compared binomial variables of the second winter (2010) with those of the first winter (2009) using Chisquare tests for equal proportion or Fisher's Exact test where numbers were small. Comparisons between continuous variables were made using Wilcoxon rank sum test. A two-sided P-value of < 0.05 was considered to be statistically significant.