Background. Since 2020, global attention has heightened towards epidemics caused by avian influenza A H5N1 virus of clade 2.3.4.4b in birds and mammals. This study presents the epidemiological history, clinical manifestations, and prognosis of a unique case infected with avian influenza A H5N1 clade 2.3.4.4b, along with the continuation of SARS-CoV-2 viral RNAs, in Eastern China.

Methods. We collected and analysed the patient’s clinical, epidemiological, and virological data. Both sputum and bronchoalveolar lavage fluid (BALF) samples were subjected to real-time RT-PCR to test for respiratory pathogens of interests, including SARS-CoV-2 and influenza virus. Influenza virus isolation and propagation were performed on embryonated eggs. Serological tests were used to determine the presence of SARS-CoV-2 antibodies. Phylogenetic analysis was constructed to explore viral evolution and origin of A/H5N1 virus.

Results. A 53-year-old female farmer with chronic bronchiectasis was hospitalized with severe pneumonia. Real-time RT-PCR revealed the presence of avian influenza A H5N1 and SARS-CoV-2 in BALF and sputum samples. Sequence analyses classified the human isolate as clade 2.3.4.4b of avian influenza A H5N1. The amino acid motif GlnSerGly at residues 226–228 of the haemagglutinin protein indicated avian-like receptor binding preference. Epidemiological investigation established that the patient had exposure to sick or dead poultry 3 days before illness onset, while no cases of human-to-human H5N1 virus transmission were identified in 31 close contacts.

Conclusion. We presented that the clade 2.3.4.4b H5N1 avian influenza virus has the potential to cross-infect humans with serious symptoms, especially in individuals already affected by COVID-19. It is indeed crucial to closely monitor the virus’s evolution in both avian populations and humans. Continued research and surveillance efforts are vital to monitor any potential changes in the virus, as well as to inform public health policies and interventions.