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:
- In 1997, the first human infections with H5N1 bird flu viruses were identified in Hong Kong.
- Buxton Bridges C. et al. “Risk of influenza A(H5N1) infection among health care workers exposed to patients with influenza A(H5N1), Hong Kongexternal icon;”
- Katz JM et al. “Antibody response in individuals infected with avian influenza A(H5N1) viruses and detection of anti-H5 antibody among household and social contactsexternal icon.”)
- In 2003, in the Netherlands, there was evidence of probable spread of H7N7 virus from two poultry workers to three family members. All three family members had conjunctivitis (pink eye) and one also had influenza (flu)-like illness.
- (M Du Ry van Beest Holle, Meijer, et al, 2005. “Human to Human Transmission of Avian Influenza /H7N7, The Netherlands, 2003external icon.”)
- In 2004, in Thailand, there was evidence of probable person-to-person spread of H5N1 bird flu virus in a family. Spread of H5N1 bird flu was associated with prolonged, very close unprotected contact between an ill child with H5N1 virus infection and her mother and aunt while the child was hospitalized. Further spread did not occur.
- (Ungchusak et al, 2005. “Probable Person-to-Person Transmission of Avian Influenza A(H5N1)external icon.”)
- In 2005, in Indonesia, limited, non-sustained person-to-person spread of H5N1 bird flu virus could not be excluded among two groups of patients who had no known contact with poultry or other animals.
- (Kandun et al, 2006. “Three Indonesian Clusters of H5N1 Virus Infection in 2005external icon.”)
- In 2006, in Indonesia, limited, non-sustained person-to-person spread of H5N1 bird flu virus may have occurred among a family cluster of eight probable or confirmed H5N1 cases.
- In December 2007, in China, limited, non-sustained H5N1 bird flu virus spread likely occurred between a sick son and his father through prolonged very close unprotected exposure while the son was in the hospital.
- Also in 2007, in Pakistan, limited, non-sustained person-to-person H5N1 virus spread likely occurred among brothers.
- (WHO, Weekly Epidemiological Record, 2008. Human cases of avian influenza A(H5N1) in North-West Frontier Province, Pakistan, October–November 2007external icon
- In 2013, person-to-person infections with (H7N9) bird flu virus were first reported in Chinaexternal icon. Yearly epidemics of person-to-person infections with H7N9 bird flu viruses in China driven mostly by contact with infected poultry at live poultry markets were reported for a number of years. A small percentage of reported cases were associated with possible limited, non-sustained person-to-person spread, mostly occurring in households between family members. However, limited, non-sustained spread of H7N9 bird flu has been reported in a few cases in hospitals.
- (Xiang, N et al, 2016.”Assessing Change in Avian Influenza A(H7N9) Virus Infections During the Fourth Epidemic — China, September 2015–August 2016“;
- Chen et al. 2016. “Nosocomial Co-Transmission of Avian Influenza A(H7N9) and A(H1N1)pdm09 Viruses between 2 Patients with Hematologic Disordersexternal icon;”
- Fang et al, 2015. “Nosocomial transmission of avian influenza A(H7N9) virus in China: epidemiological investigationexternal icon.”
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.
