Past Examples of Possible Limited, Non-Sustained Person-to-Person Spread of Bird Flu

Avian influenza (“bird flu”) viruses rarely infect people. Most previous bird flu virus infections in people have occurred following close, prolonged, and unprotected (e.g., no gloves or medical mask) contact with infected birds or environments contaminated by their saliva, mucous or poop. For any one person, the risk of infection depends on exposure and specifically on how close and how long the exposure is. Even when people have been infected with bird flu viruses there has very rarely been onward spread from one infected person to another person. Detailed public health investigations are used to determine whether person-to-person spread of bird flu virus has occurred. Below are a few examples of this happening in other countries, however, when it has happened, it has not led to sustained (ongoing) spread among people.

Examples of likely person-to-person spread of bird flu:

Person-to-person spread of other non-human (animal-origin) flu Type A viruses can range from occasional, limited, and non-sustained spread of one or more generations without further spread (“dead-end transmission”), to efficient and sustained person-to-person spread. Easy and sustained (ongoing) spread of non-human flu Type A viruses (including bird flu viruses) among people in the community is needed for a flu pandemic to begin.