Etiology of pediatric community-acquired pneumonia across Mycoplasma pneumoniae epidemic periods

Community-acquired pneumonia (CAP) remains a leading cause of hospitalization and antibiotic use in children, yet etiologic data during Mycoplasma pneumoniae epidemic periods—now resurging globally after the COVID-19 pandemic—remain scarce. We conducted a nationwide prospective surveillance study across 17 hospitals in Korea between September 2023 and May 2025, enrolling 740 children with CAP. Etiology was determined using standardized criteria: pyogenic bacteria by culture with central adjudication, atypical bacteria by polymerase chain reaction (PCR) and serology, and viruses by PCR (excluding human rhinovirus/enterovirus, bocavirus, and coronavirus, given their uncertain causal role). An etiologic pathogen was identified in 541 children (73.1%), with atypical pathogens predominating (43.6%), followed by viral (26.8%) and pyogenic (2.7%) etiologies. During the peak M. pneumoniae epidemic period (June 2024–January 2025), atypical CAP accounted for 57.0% of cases, whereas the odds of pyogenic CAP were 66% lower than in other periods (Firth penalized odds ratio, 0.34; 95% CI, 0.13–0.81). In exploratory multivariable analysis, pyogenic CAP was associated with prolonged hospitalization, respiratory support, and intensive care unit admission. These findings may inform empirical antibiotic decision-making in hospitalized children with CAP during M. pneumoniae epidemic periods, while early recognition of the rare but severe pyogenic CAP remains essential.