Epidemiology and Genetic Diversity of Human Metapneumovirus in Patients with Severe Acute Respiratory Infection from 2023 to 2024 in Ningxia, China

Background: Human metapneumovirus (HMPV) is a major pathogen responsible for causing severe acute respiratory infections (SARI). Whole-genome sequencing can better identify transmission events and outbreaks. In this study, we aimed to investigate the epidemiology and genetic diversity of HMPV in SARI cases in Ningxia, China. Methods: We collected respiratory tract samples from hospitalized patients with SARI from October 2023 to September 2024 in Ningxia, China. Nasopharyngeal swabs were tested for respiratory viruses with qRT-PCR. Whole-genome sequences were determined for samples with high viral loads using an amplicon-based method. Results: We enrolled 2873 SARI patients from October 2023 to September 2024, and found an HMPV-positive proportion of 3.06% (88/2873). Children aged 4 years were particularly susceptible to HMPV infection, with a positive proportion of 10.92% (13/119). HMPV exhibits distinct seasonal characteristics, consistent with its established epidemiological pattern, with a peak incidence occurring during winter months. Sixteen complete HMPV genome sequences were obtained. Among these, 81.25% (13/16) were identified as genotype A (A2.2.2: 92.31%, 12/13; A2.2.1: 7.69%, 1/13) and 18.75% (3/16) as genotype B1. Notably, the dominant strain was 111nt-dup in genotype A2.2.2. Sequence analysis of HMPV genes revealed divergent G-gene sequence identities between different genotypes. Additionally, the potential glycosylation sites of the G protein varied across genotypes. Conclusions: In this study, we found that the 111nt-dup strain was the dominant one in genotype A, and multiple genotypes co-circulated in Ningxia from October 2023 to September 2024. The HMPV G protein exhibited the highest level of inter-strain diversity between genotypes. These findings provide valuable insights into the prevention and control of HMPV infections in China.