Severe Bacterial Infections and Sepsis Among Hospitalized Older Adults in São Paulo State, Brazil, 2015-2025: A Population-Based Study With a Descriptive Time-Series Component

ObjectiveThe objective of this study was to describe temporal trends, hospitalization rates, clinical profile, and factors associated with in-hospital mortality among older adults (≥60 years) hospitalized for severe bacterial infections and sepsis in São Paulo State, Brazil, 2015-2025, and to characterize the subgroup with sepsis in the strict sense. MethodsPopulation-based observational study using Brazilian Hospital Information System (SIH/SUS) records, including 1,310,296 hospitalizations.Hospitalization rates per 100,000 inhabitants used population estimates from the Brazilian Institute of Geography and Statistics.The annual temporal trend was modeled with quasi-Poisson regression, including a population offset and correcting for overdispersion; prepandemic (2015-2019) and post-pandemic recovery (2022-2025) subperiods were modeled separately given the nonlinear pattern of the series.Factors associated with in-hospital mortality were assessed with multivariable logistic regression (age band, sex, ICU admission, and comorbidity), with a sensitivity analysis excluding ICU admission. ResultsMean age was 76.2 years (SD 9.6).After adjusting for population growth and overdispersion, the overall hospitalization rate showed no statistically significant linear trend from 2015 to 2025 (incidence rate ratio (IRR) 1.005 per year, 95% CI 0.983-1.028);the series was nonlinear, with a stable pre-pandemic rate (IRR 0.996/year, 95% CI 0.988-1.003),a marked nadir in 2020-2021, and a statistically significant recovery-period increase of approximately 5.6% per year from 2022 to 2025 (IRR 1.056/year, 95% CI 1.030-1.082).In-hospital mortality was 424,156 (32.37%), rising from 105,790 (28.06%) at 60-69 years to 48,731 (40.66%) at ≥90 years (p < 0.001), while ICU admission fell from 87,467 (23.2%) to 8,270 (6.9%) across the same range.Patients aged ≥90 years had higher adjusted odds of death (OR 2.56; 95% CI 2.52-2.60),an association that persisted, though attenuated (OR 1.91; 95% CI 1.88-1.93), in a sensitivity analysis excluding ICU admission; male sex carried a small but significant increase in odds (OR 1.08; 95% CI 1.07-1.09).Sepsis in the strict sense accounted for 248,525 (19.0%) of hospitalizations, with 159,503 (64.18%) in-hospital lethality, roughly twice that of the broad cohort. ConclusionsThe overall hospitalization rate for severe bacterial infections and sepsis among older adults in São Paulo showed no statistically significant linear trend once adjusted for population growth, but the series was markedly nonlinear: a stable pre-pandemic rate was followed by a pandemic-related nadir and a statistically significant post-pandemic recovery-period increase exceeding pre-pandemic levels.Mortality rose sharply with age as intensive care access fell, and sepsis in the strict sense formed a markedly more lethal core within this broader burden, underscoring the need for early recognition, vaccination, and adapted geriatric and intensive care capacity.