Is H7N9 virus spreading from person-to-person?
China has conducted extensive case investigations of people infected with H7N9 virus and their close contacts and has found no evidence of "sustained" person-to-person spread at this time. Ongoing spread of a virus among humans is necessary for a pandemic to occur. However, a small number (approximately 7%) of confirmed H7N9 cases in China have occurred in small clusters, and some cases were associated with likely limited, non-sustained person-to-person spread of H7N9 virus.
"Limited" virus spread usually refers to when a virus from an animal host infects a person and then spreads to a caretaker or close contact of that person but not any further. Based on what we know about other avian influenza viruses, some limited, non-sustained person-to-person spread of H7N9 virus is not surprising.
Limited person-to-person spread of other avian influenza viruses is thought to have occurred rarely in the past in several countries, most notably with avian influenza A(H5N1) virus infection, following prolonged, close, unprotected exposure to a very sick patient. This highlights the importance of good infection prevention and control measures for hospitalized patients with H7N9 virus infection.
CDC expects that additional limited person-to-person transmission events with the H7N9 virus could occur in the future if the virus continues to spread between birds and people. CDC and global public health experts are monitoring H7N9 viruses in China for changes that could allow them to spread more easily among people.
Is it possible that this virus will spread from person-to-person?
Yes. Based on what we know about human infections with other bird flu viruses, it's possible and even likely that there will be some limited, non-sustained person-to-person spread of H7N9 virus. The important factor will be to determine whether H7N9 viruses gain the ability to spread easily from one person to another. Sustained person-to-person spread of a novel influenza A virus is needed for a pandemic to start. Health officials are watching the situation closely for this.