As of May 3, 2013 Chinese officials reported four family "cluster" cases where two or three members of the family were infected. Officials have offered a number of possibilities for the infections and have not ruled out human-human transmission. However, the data are not clear as family members appear to have been infected at different times, short and long lag times which means they may have been infected by the same source rather than each other.
Thus far the majority of infections have occurred in areas with comparatively high number of poultry carrying the virus, per Chinese officials in the area.
May 23, 2013 Chinese, US, and Canadian researchers reported limited aerosol transmission of the virus in ferrets. Ferrets are used for this research as they mimic humans with respect to contracting the virus. This is good news with respect to human-to-human transmission of the virus at this time. The researchers also found H7N9 virus shedding occurred before most clinical signs developed, a pattern seen with pandemic and seasonal flu."
The also cautioned should H7N9 becomes endemic in China's poultry, the likely source of the of the virus, the risk of the virus evolving to become more transmissible among humans or spreading to pigs would increase.