Epidemiological characteristics of human parainfluenza virus infections and phylogenetic analysis of human parainfluenza virus type 3 isolated from children with respiratory tract infections from 2020 to 2022 in Zhejiang, China.

Human parainfluenza viruses (HPIVs) are a major cause of pediatric respiratory hospitalizations worldwide. HPIV-3 is one of the most common subtypes of HPIV. In this study, we retrospectively analyzed the respiratory pathogen detection results for 23,775 children with ARIs who were treated in Zhejiang Province from January 2020 to December 2022, 610 HPIVs-positive specimens were selected for parainfluenza virus typing, and 35 HPIV-3-positive samples were selected for HN gene sequencing and analysis. In total, 1383 of the specimens were positive for HPIV, resulting in a detection rate of 5.82%. During this period, the detection rate was the highest in 2020, at 7.77%. The detection rate in autumn was 9.17%, surpassing those in other seasons. Among the different age groups, schoolchildren had the lowest detection rate of 1.75%. HPIV-3 was the predominant subtype, accounting for 76% of HPIV-positive cases. The nucleotide and amino acid sequence identity of the 35 HPIV-3 HN genes that were examined ranged from 97.0-100.0% and 98.6-100.0%, respectively. Phylogenetic analysis revealed that 27 isolates belonged to the C3a subtype and that eight belonged to the C3b subtype. A total of 171 nucleotide variations and 30 amino acid variations were identified among the 35 isolates. These findings confirm that HPIV, especially HPIV-3, was a significant pathogen in acute respiratory infection among pediatric patients in Zhejiang from 2020 to 2022. The observation of high sequence similarity and relatively stable genetic evolution of HPIV-3 in this region provides valuable insights into the molecular and epidemiological characteristics of this virus.