XK and infection: At 1 h post infection (p.i.), cultures were washed twice with Dulbecco's modified minimum essential medium (DMEM) and incubated in DMEM with or without 2 μM of oseltamivir carboxylate (GS4071) from 1 to 13 h p.i. The 50% inhibitory concentration of GS4071 against NA activity was almost the same between H10/chicken and H3/Osaka viruses, and NA activity of both viruses was completely suppressed by 2 μM GS4071 (data not shown).