Viral RNA was extracted from 140 ml plasma/lung aspirates using QIAamp Viral RNA Mini Kit (Qiagen, Germany) as per the manufacturers' instructions. For viral RNA quantitation, CDC primers and probe were used. The target HA gene from an Indian isolate was cloned to obtain in vitro transcripts, serial 10-fold dilutions of the RNA were used to generate a reference curve. A linear relationship was obtained from 10 10 -10 2 starting copies/ reaction (r 2 = 0.99), the detection limit being 100 copies.