Out of the 541 enrolled patients, 447 (83%) had a RT-PCR laboratory confirmation of influenza A virus infection on the day 0 specimen, with a mean viral load of 4.38 log 10 cgeq/ml (interquartile range [IQR] 3.75-5.30). All the day 0 specimens were GAPDH RT-PCR positive with a mean value of 3.88 log 10 copies/ml.