Age-stratified clinical features and factors associated with severe pneumonia in hospitalized children with human metapneumovirus–associated lower respiratory tract infection

Human metapneumovirus (hMPV) is a major cause of lower respiratory tract infection (LRTI) in children, yet age-stratified analyses across the full pediatric age range and the associations between pathogen co-detection and disease severity remain incompletely characterized. We aimed to delineate the age-related clinical features of hMPV-LRTI and identify factors associated with severe pneumonia. This retrospective study included children aged 0 to < 18 years hospitalized with hMPV-LRTI at Children’s Hospital Affiliated to Shandong University during 2023–2025. Pathogens were identified by targeted next-generation sequencing (T-NGS). Clinical, laboratory, radiological, and pathogen co-detection features were compared across five age groups. Associations between prespecified covariates and severe pneumonia were examined using multivariable logistic regression, with selected laboratory variables analyzed continuously. Among 1,611 children (57.4% male), 301 (18.7%) had severe pneumonia, and 36 (2.2%) were admitted to the intensive care unit (ICU). Infants aged 0–6 months had the highest ICU admission rate (7.9%), whereas children > 6 years had the highest proportions of atelectasis (22.4%), unilateral involvement (65.7%), and severe pneumonia (31.0%). In the primary model, atelectasis (adjusted odds ratio [aOR] = 47.52), underlying disease (9.49), consolidation (6.82), fever (3.29), wheezing (2.50), Mycoplasma pneumoniae (MP) co-detection (1.90), higher absolute neutrophil counts (1.47 per 5 × 10⁹/L), and higher C-reactive protein levels (1.14 per 10 mg/L) were associated with higher odds; higher absolute monocyte counts (0.71 per 1 × 10⁹/L) and bacterial co-detection (0.60) were associated with lower odds. The large radiological associations may partly reflect overlap with the extent-based severity criteria. MP co-detection increased from 6.0% in infants aged 0–6 months to 50.0% in children > 6 years. The overall age-group term did not reach statistical significance. Clinical and radiological manifestations of hMPV-LRTI varied across age groups. MP co-detection was more frequent in older children and was associated with higher odds of severe pneumonia after multivariable adjustment. These findings may inform age-specific clinical assessment, with attention to respiratory status in young infants and, in school-aged children, peri-admission chest imaging when clinically indicated and further clinical and microbiological evaluation when MP is co-detected.