Viral metagenomic analysis of human bocavirus in pediatric pneumonia: detection pattern and genetic characterization

Human bocavirus (HBoV) is frequently detected in pediatric respiratory samples, but its clinical role remains difficult to interpret because of asymptomatic shedding and frequent co-detection with other pathogens. Data from bronchoalveolar lavage fluid (BALF), which more directly reflects the lower respiratory tract, remain limited.

This retrospective study analyzed 179 BALF samples collected from pneumonia patients in the Jiangnan region of China between July and December 2025. Metagenomic next-generation sequencing (mNGS) was used for HBoV detection, mNGS-derived abundance estimation, genotype assignment, and genome coverage analysis. VP1 and NS1 gene fragments were used for phylogenetic analysis, and recombination screening was performed using RDP4.

Using the predefined ≥10-read mNGS screening threshold, HBoV signals were detected in 22 of 30 pediatric samples (73.3%; 95% CI, 54.1-87.7%) and in none of the 149 adult samples (0%; 95% CI, 0-2.45%), showing an age-related detection pattern in this cohort (Fisher's exact test, P = 6.91 × 10^-²²). HBoV1 was assigned as the dominant genotype in all HBoV mNGS signal-positive samples. RPM values varied among these samples, but they should be interpreted as mNGS-derived relative abundance rather than absolute viral load. Genome coverage analysis and partial VP1/NS1 phylogenetic placement provided additional support for HBoV1 read-based detection and genotype assignment. RDP4 analysis did not detect recombination events involving the study-derived VP1 or NS1 fragments.

HBoV1 was frequently detected in pediatric BALF samples in this retrospective cohort, suggesting that HBoV1 signals may be relevant to the interpretation of some pediatric lower respiratory tract samples. However, because qPCR validation, healthy controls, and a comprehensive multi-pathogen co-infection assessment were not included, these data do not establish HBoV1 as the direct causative agent of pneumonia. Larger studies with quantitative validation and more complete clinical data are needed.