Subgroup analysis of clinical variables for laboratory-confirmed influenza, stratified by age and influenza activity: multivariate analysis (odds ratios (95% CI)).

†Indicates that the variable was not entered in logistic regression analysis as it was not significant in univariate analysis.
*Indicates that the p-value of the data <0.05 in logistic regression analysis.
Note: Epidemic period (25 December 2011 [week 53]–5 May 2012 [week 18]) (n = 1811), non-epidemic period (25 September 2011 [week 40]–24 December 2011 [week 52], 6 May 2012 [week 19]–2 July 2012 [week 22]) (n = 147).