Clinical epidemiology of community-acquired pneumonia in children before, during, and after the COVID-19 pandemic, and independent risk factors analysis for severe community-acquired pneumonia.

Background: The COVID-19 pandemic may have created an 'immunity debt', altering the epidemiology and aetiology of paediatric community-acquired pneumonia (CAP). However, multi-centre data on these changes and contemporary risk factors for severe CAP remain limited. We therefore aimed to analyse clinical characteristics and pathogen composition of CAP in children before, during, and after the COVID-19 pandemic, and to identify independent risk factors associated with severe CAP. Methods: We collected clinical data from paediatric inpatients diagnosed with CAP at 13 hospitals in 13 provinces of China between August and October 2018 2018 (before the COVID-19 pandemic), 2020 (during the pandemic), and 2023 (after the pandemic). We used a multivariate COX regression model to identify independent risk factors for severe CAP. Results: Our sample comprised 5180 children hospitalised with CAP, with fever and cough being the main clinical symptoms. The number of school-aged children with CAP was significantly higher after compared to before and during the pandemic, while cellular immune function was significantly reduced (P < 0.05). The proportion of viral infections increased from 7.4% before to 20.1% after the pandemic; mycoplasma infections rose significantly from 36.3% to 41.9%, while other bacterial infections increased from 4.9% to 9.7%. The proportion of bacterial infection was highest among infants (11%) and toddlers (9.4%). Viral infection (18.9%), virus-viral co-infections (3.1%), viral-bacterial co-infections (3.3%), and bacteria-bacterial co-infections (1.8%) were more common among preschool children, while mycoplasma infections (59.8%), mycoplasma-viral co-infections (10.5%), or mycoplasma-bacterial co-infections (4.6%) were more frequent among school-aged children. We identified wheezing (hazard ratio (HR) = 1.551), chest pain (HR = 3.144), haemoptysis (HR = 4.854), Klebsiella pneumoniae (HR = 4.236), Acinetobacter baumannii (HR = 4.432), influenza B virus (HR = 2.338), and adenovirus infection (HR = 2.895) as risk factors for severe CAP. Conclusions: We observed a shift in the epidemiology of CAP in children following the pandemic, with altered immune responses and pathogen profiles. These findings emphasise the need for targeted treatment strategies in paediatric patients in the post-COVID-19 context to reduce the burden of severe CAP.