A higher percentage of oropharyngeal compared to cloacal swabs were positive for influenza infection. This observation raises concern regarding the mode of transmission for these viruses. Several H9N2-subtype viruses can transmit through direct contact with infected chickens and ferrets [33, 34] . It is this route of infection that likely produced the H9N2-subtype infections that have been reported in humans [6, 7, 22] . However, aerosol transmission has been observed in chickens infected with a Beijing/1-like virus (A/Chicken/Shanghai/F/98 [H9N2]) [33] , and this could explain the high prevalence of the H9N2 subtype in the live-bird markets of Bangladesh. Aerosol transmission has not been observed between ferrets that were infected with H9N2subtype viruses, suggesting that transmission between mammals is currently limited [34] .