Avian Influenza A(H5N1) - Cambodia
On 20 August 2024, the IHR NFP of the Kingdom of Cambodia notified WHO of one case of human infection with influenza A(H5N1) in a 15-year-old with no underlying medical conditions, from Prey Veng Province. The child had an onset of fever on 11 August 2024. On 17 August, the patient was hospitalized in Phnom Penh at a severe acute respiratory infection (SARI) sentinel site. On admission, the patient presented with a fever, cough, sore throat, and difficulty breathing, and on the same day, treatment with oseltamivir was initiated. Nasopharyngeal and oropharyngeal swab specimens were collected on 17 August, and the patient died on 20 August.
Swab specimens collected on 17 August arrived at the National Institute of Public Health of Cambodia on 19 August and tested positive for influenza A(H5N1) by quantitative reverse transcription polymerase chain reaction (RT-qPCR) on 20 August. The results were confirmed by the Institut Pasteur du Cambodge (IPC) the same day. The sample was successfully sequenced, and phylogenetic analysis of the haemagglutinin (HA) gene showed the virus to be H5 clade 2.3.2.1c, similar to the viruses circulating in Cambodia and Southeast Asia since 2013-2014. However, its internal genes belong to H5 clade 2.3.4.4b viruses. This novel reassortant influenza A(H5N1) virus has been detected in human cases reported in Cambodia since late 2023.
According to early investigations, there were reports of dead poultry in the village about five days before the patient’s onset of illness. The patient's family was given some of these chickens for consumption and the girl was exposed to the chicken while preparing food.
The Cambodian Communicable Disease and Control Department (CDC), Ministry of Health, and local Rapid Response Team conducted further investigations. Six close contacts were identified, and oseltamivir was provided to them. All close contacts are being monitored and are asymptomatic. Further investigations and response measures are ongoing for public and animal health and the environment. Test results for samples collected from chickens and ducks from the village are pending.
Avian influenza A(H5N1) was detected for the first time in Cambodia in December 2003, initially affecting wild birds. From then until 2014, sporadic human cases were reported due to transmission from poultry to humans, either directly or indirectly through contaminated environments. Between 2014 and 2022, there were no reports of human infection with A(H5N1) viruses. However, the re-emergence of human infections with A(H5N1) viruses in Cambodia was reported in February 2023; six cases were reported that year. This case is one of 10 human cases of influenza A(H5N1) infection reported in Cambodia in 2024. Two of the 10 cases were fatal, and nine involved persons under 18 years of age. From 2003 to the present, 72 cases of human infection with influenza A(H5N1), including 43 deaths (CFR 59.7%), have been reported in the country.
