The H9N2 subtype of avian influenza virus (AIV) is widely distributed in poultry and occasionally infects humans, posing a potential public health risk. While most infections are mild, severe disease can occur in vulnerable individuals. We describe a case of H9N2 infection in a lung transplant recipient who developed severe pneumonia and respiratory failure. Viral isolation and full-genome sequencing were conducted, followed by phylogenetic, evolutionary, and structural analyses to characterize the virus. The isolate was also compared with environmental samples monitored in our surveillance program. Genomic sequencing identified an H9N2 strain carrying two hemagglutinin (HA) substitutions, Y264H and T195S, a combination not commonly reported in circulating avian strains but recently detected in our environmental surveillance samples. Phylogenetic analysis indicated that the PB1 and PB2 genes of the H9N2 virus were closely related to those of avian H3N8 viruses. Structural modeling suggested that the HA substitutions may influence receptor-binding stability, though their impact on viral adaptation requires further investigation. This case illustrates that H9N2 infection can cause severe disease in immunocompromised patients and provides genomic and structural insights into a reassortant H9N2 strain detected in humans. The close similarity of the HA gene sequence between this strain and environmental isolates highlights the importance of continued surveillance of avian influenza viruses.

Background: The post-pandemic era has brought about marked shifts in the circulation patterns of respiratory pathogens. Nevertheless, comprehensive epidemiological data on acute respiratory infections (ARIs) covering both influenza-like illness (ILI) and severe acute respiratory infection (SARI) remain scarce for southern China. This study aimed to characterize the epidemiological profiles and pathogen spectra of ARIs in Guangzhou, China, from January 2024 to December 2025. Methods: Respiratory specimens were collected from ILI outpatients and SARI inpatients attending two sentinel hospitals in Guangzhou. All specimens were tested for 23 respiratory pathogens using the NxTAG™ Respiratory Pathogen Panel. Statistical analyses were conducted to explore pathogens distribution stratified by patients’ demographic characteristics. Results: Among 4,635 ARI cases, the overall pathogen detection rate was 47.96% ( n = 2,223). Influenza virus (IFV, 14.5%) and human rhinovirus (HRV, 10.1%) were predominant. In ILI cases, IFV (19.1%) and HRV (10.9%) were most common; in SARI cases, HRV (8.5%) and respiratory syncytial virus (RSV, 8.2%) prevailed. Marked age-dependent variations were observed: RSV and bocavirus (BOV) primarily infected preschool children, whereas SARS-CoV-2 and IFV were more commonly detected in adults and older individuals. Seasonally, an earlier IFV peak occurring in December and an out-of-season RSV epidemic in 2025 characterized by a summer peak were observed. Co-infections occurred in 9.76% of positive cases, with IFV/HRV most frequent. Positivity rates were higher in ILI (54.1%) than SARI (34.5%). Logistic regression identified advanced age (≥60 years), RSV in children age < 5 years and MP were associated with SARI. Conclusion: These findings reveal that the spectrum of respiratory pathogens in Guangzhou is characterized by dynamic patterns of co-circulation and alternating predominance across different time periods and populations. Highlighting the need for age-specific and seasonally tailored interventions and comprehensive diagnostic tools.

Objective: We aimed to elucidate the epidemiological characteristics and co-infection status of HBoV in Guangzhou and to investigate the potential recombination events and alterations in antigenic properties among circulating HBoV strains. Methods: Utilizing respiratory specimens collected from patients at sentinel surveillance hospitals in Guangzhou between August 2023 and December 2025, multiplex pathogen detection was performed. We describe the temporal and demographic distribution of HBoV in Guangzhou and determine its co-infection patterns. Subsequent sequence analysis focused on identifying potential recombination events and characterizing antigenic properties. Results: The epidemiological features of HBoV in Guangzhou exhibited a primary epidemic peak around the autumn season, followed closely by a secondary peak. HBoV infection was predominantly observed in children under three years of age. Co-infections with rhinovirus and parainfluenza virus were common. Whole-genome sequencing yielded 15 complete HBoV genome sequences. Recombination analysis and verification suggested potential recombination events in two of these sequences. A comparative analysis of the antigenic characteristics of one identified recombinant strain, GZ-2024-20891, against its putative parental strains and domestic prevalent strains revealed potential alterations in its antigenic characteristic. Conclusions: Bocavirus is highly prevalent among young children under 3 years of age, with a secondary peak following the main epidemic peaks around autumn in Guangzhou. Genetic recombination and potential antigenic alteration were detected in bocavirus.