Severe Bacterial Infections and Sepsis in Children and Adolescents in São Paulo, Brazil: A Population-Based Time-Trend Study, 2015-2025

Background: Severe bacterial infections and sepsis are leading causes of pediatric hospitalization and death worldwide, yet recent Brazilian population-based data spanning the COVID-19 pandemic and distinguishing severe bacterial infection broadly from strict septicemia remain scarce.Objectives: To describe hospitalization trends, mortality, and factors associated with in-hospital death among children and adolescents with severe bacterial infections and sepsis in São Paulo State, Brazil, from 2015 to 2025, comparing the broad cohort with a strict-sepsis subgroup.Methods: Population-based, repeated cross-sectional study in São Paulo State, Brazil, 2015-2025, using Hospital Information System of the Brazilian Unified Health System (Sistema de Informações Hospitalares do Sistema Único de Saúde, SIH/SUS) records for hospital admissions of individuals aged 28 days to 19 years.The primary exposure was age group (infant, preschool-age, school-age, adolescent); the primary outcome was in-hospital death.Poisson regression estimated the annual trend in the number of admissions.Crude relative risks (RR) were calculated directly from contingency data; adjusted RR (aRR) were obtained by predictive marginal standardization from a multivariable logistic model, with modified Poisson regression (robust variance) as a sensitivity analysis.Results: Among 553,218 hospitalizations (277,644; 50.2% male), overall case fatality was 1.6% (8765 deaths).Compared with infants (case fatality 1.8%; 3038/170,495), adolescents had over double the risk of death (crude RR 2.16, 95% CI 2.06-2.27),while preschool-age (RR 0.47, 95% CI 0.44-0.50)and school-age children (RR 0.59, 95% CI 0.54-0.63)had lower risk.Male sex carried modestly higher risk (RR 1.16, 95% CI 1.11-1.21),and comorbidity (49,952; 9.0% of admissions) more than tripled risk (RR 3.22, 95% CI 3.07-3.38).The number of admissions declined over the study period (Poisson regression trend ratio 0.96 per year, 95% CI 0.96-0.97),with a pronounced, non-linear drop during the pandemic and partial recovery thereafter.The strict-sepsis subgroup comprised 27,181 admissions (4.9% of the cohort) but had a case fatality of 14.7% (3985 deaths), nine times that of the broad cohort.Conclusions: Severe bacterial infections impose a substantial, age-concentrated hospital burden among Brazilian children, while strict sepsis, though comparatively uncommon, remains markedly lethal.Distinguishing these entities is important for surveillance and resource planning.