Factors associated with severe COVID-19 among children aged <12 years in Fuzhou, China: a frequency-matched case-control study

Background Evidence on social, preventive, and clinical factors associated with severe pediatric COVID-19 remains limited in regional Chinese surveillance settings. We evaluated these factors among children aged <12 years in Fuzhou. Methods We conducted a frequency-matched case-control study of 347 severe cases and 694 non-severe controls identified from sentinel hospitals and the China Disease Prevention and Control Information System between January 2020 and August 2025. Controls were sampled at a 1:2 ratio by broad onset period, geographic sampling stratum, and parental education level. Group differences were assessed using Pearson's chi-square test. Given frequency matching without individual matched sets, unconditional multivariable logistic regression was used. Concurrent clinical manifestations were interpreted as warning indicators rather than antecedent etiologic risk factors. Results The selected sample comprised 1,041 children (347 severe cases and 694 non-severe controls). Severe disease was positively associated with male sex (adjusted odds ratio [aOR] 1.897, 95% CI 1.451-2.481), age <=5 years (aOR 1.578, 95% CI 1.209-2.061), home-based/preschool care (aOR 2.771, 95% CI 2.033-3.776), rural residence (aOR 2.470, 95% CI 1.858-3.283), delayed consultation of >2 days (aOR 1.902, 95% CI 1.388-2.605), obesity (aOR 2.028, 95% CI 1.398-2.941), chronic respiratory disease (aOR 3.425, 95% CI 2.558-4.586), and metabolic or endocrine disease (aOR 3.928, 95% CI 2.826-5.460). Vaccination (aOR 0.537, 95% CI 0.363-0.793) and disease-prevention awareness (aOR 0.395, 95% CI 0.299-0.522) were inversely associated with severity. Fever lasting >3 days, dyspnea, and altered mental status were more frequent in severe cases and were treated as concurrent clinical warning indicators. Conclusion Within this selected regional case-control sample, severe pediatric COVID-19 was associated with demographic, caregiving, healthcare-access, and pre-existing health factors. Vaccination and disease-prevention awareness were inversely associated with severity. The identified clinical manifestations serve as early-recognition and triage cues rather than baseline risk factors. Temporal and selection-related limitations warrant cautious generalization.