Abstract
<title>Abstract</title> <p>Background Human metapneumovirus (hMPV) is an important cause of lower respiratory tract infection in infants, but data on infants with respiratory bacterial co-detection are limited. We aimed to describe the clinical and microbiological characteristics of this population and to explore factors associated with severe disease. Methods We conducted a single-center retrospective study of infants aged 12 months or younger who were hospitalized at Henan Children's Hospital between October 2024 and March 2025 with hMPV pneumonia and clinically adjudicated respiratory bacterial co-detection. Demographic, clinical, laboratory, imaging, treatment, and 6-month follow-up data were extracted from medical records. Severe disease was classified according to the pediatric community-acquired pneumonia guideline and the discharge diagnosis. Group comparisons used chi-square or Fisher's exact tests and the Mann–Whitney U test. Exploratory logistic regression was performed; the primary model excluded lethargy because it overlapped with severity criteria, and a secondary warning-sign model included lethargy. Results Among 309 infants, 190 (61.5%) were male and 42 (13.6%) were classified as severe cases. Streptococcus pneumoniae was the most frequently co-detected bacterium. Among 143 infants who underwent chest CT, multilobar pneumonia (90.9%) and ground-glass opacity (56.6%) were the most common findings. In the primary exploratory model, artificial feeding (OR 2.60, 95% CI 1.27–5.34), underlying diseases (OR 2.43, 95% CI 1.14–5.21), and lower albumin levels (OR 0.85 per 1 g/L increase, 95% CI 0.78–0.94) were associated with severe disease. In the secondary model, lethargy was strongly associated with severe presentation (OR 5.02, 95% CI 2.38–10.62) and should be interpreted as a warning sign rather than an independent causal factor. Conclusions Underlying diseases, artificial feeding, and lower albumin levels may help identify infants with hMPV pneumonia and respiratory bacterial co-detection who require closer monitoring. Lethargy should be regarded as an early warning sign. These association-based findings require confirmation in multicenter prospective studies with standardized pathogen quantification and adjudication.</p>