Upon adjustment for confounders , multivariate logistic regression models showed that FluA - p was associated with an increased risk of invasive ventilation ( adjusted odds ratio [ aOR ] : 3 . 824 , 95 % confidence interval [ CI ] : 2 . 279 - 6 . 414 ; P < 0 . 001 ) , admittance to intensive care unit ( aOR : 1 . 630