Five-to two-hundred microliters of clinical sample was centrifuged at 17,000 g for 10 minutes. The supernatant was filtered through a 0.22 mm Ultrafree MC spin filter (Millipore) at 2000 g for 2 minutes and DNase treated (6 U DNaseI Amplification grade, Invitrogen) for 1K hours at room temperature while shaken in a Thermomixer (AH Diagnostics). The viral NA was extracted using the PureLink Viral RNA/DNA kit (Invitrogen), without the addition of carrier RNA. The extracted viral NA was eluted with 20-30 ml DNase/RNase-free sterile water, and stored at 220uC or immediately used.