Currently, HPAI Asian H5N1 virus does not transmit efficiently from person to person.
Some cases of limited, non-sustained human-to-human transmission have likely occurred.
Clusters of human Asian HPAI H5N1 cases, (usually 2 cases but ranging from 2-8 cases per cluster), have been identified in several countries. Nearly all of the cluster cases have occurred among blood-related family members, especially those living in the same household. Whether such infections are related to genetic or other factors is currently unknown. While most people in these clusters have been infected with Asian HPAI H5N1 virus through common source exposures such as direct or close contact with sick or dead poultry or wild birds, limited non-sustained human-to-human transmission of Asian HPAI H5N1 virus cannot be excluded and likely occurred in some clusters. In cases where limited human-to-human transmission of Asian HPAI H5N1 virus is thought to have occurred, spread has occurred after a very long period of unprotected close contact (hours in length) with a very sick blood-related family member (e.g., mother-daughter or brother-brother). This has been reported to have occurred in a home and in a hospital room.
For example, a report in 2004 from Thailand, describes probable limited human-to-human HPAI Asian H5N1 virus spread in a family resulting from prolonged and very close contact between an ill child and her mother in a hospital room.1 Limited person-to-person spread of Asian HPAI H5N1 virus from a son to his father in a hospital room was also reported in China in 2007.2 In 2006, WHO reported evidence of non-sustained human-to-human-to-human Asian HPAI H5N1 virus spread in Indonesia. In this situation, eight people in one family were infected. The first family member is thought to have become ill through contact with infected poultry. This person then infected six family members through close prolonged contact. One of those six people (a child) then infected another family member (his father). All of the cases were blood-related family members. No further spread outside of the exposed family was identified.3 Finally, human-to-human transmission of Asian HPAI H5N1 virus was also reported in Pakistan among three brothers in 2007.4