Four recent human infections with highly pathogenic avian influenza (H5N1) (bird flu) viruses have been reported in Cambodia. These are the first human infections with the H5N1 virus confirmed in Cambodia in 2024. The four infected patients, three children (one of whom died) and one adult, were all confirmed in late January or early February.
All patients had a recent history of exposure to sick poultry (birds raised as livestock) or dead poultry prior to illness onset.
At this time, there are no indications of human-to-human transmission associated with these four cases of H5N1 virus infection in Cambodia.
The first two patients were epidemiologically unrelated and were admitted to different Cambodian hospitals, but both recovered and were discharged home. Both patients had been exposed to sick birds prior to the onset of symptoms; a 3-year-old child patient’s backyard chickens were found dead around her home, and a 69-year-old patient raised poultry and fighting cocks, three of which tested positive for H5N1.
The third patient died shortly after being transported to a pediatric hospital in the capital; the fourth patient was admitted for observation and treatment; the third and fourth patients were siblings, but lived in different villages.
The fourth patient’s family brought dead poultry to the third patient’s family, and both siblings were exposed.
An investigation is underway to monitor these two close contacts and identify further transmission. The U.S. CDC is working with the Ministry of Health’s Cambodian Department of Communicable Disease Control (C-CDC), the National Institute of Public Health (NIPH) of Cambodia, the Ministry of Agriculture, Forestry and Fisheries, Institut Pasteur du Cambodge (IPC), the World Health Organization (WHO), the United States Agency for International Development (USAID), the Food and Agriculture Organization, and the Wildlife Conservation Society of Cambodia to address these sporadic human infections.
Genetic sequencing of specimens from the first and third patients identified both H5N1 viruses as H5 clade 2.3.2.1c, which has been circulating among birds and poultry in Cambodia for many years. This is different from the H5N1 virus that has circulated widely in poultry in several world regions.
Genetic sequencing of the specimen from the fourth patient is ongoing.
Four of the six human infections with H5N1 viruses in Cambodia during 2023 were fatal; since the first infection was reported in 2003, 64 cases have been reported in Cambodia, including 41 deaths.
Further sporadic human infections are not unexpected in persons with direct or close unprotected exposure to poultry infected with the H5N1 virus in areas where the H5N1 virus is endemic among poultry.