Factors Associated with Mortality in Adults ≥65 Years with Bacteremia in a Tertiary Referral Care Hospital in Manizales/Colombia, 2020–2023

Background Bacteremia in older adults represents a highly complex clinical condition with elevated mortality, driven by population aging, multimorbidity, immunosenescence, and atypical clinical presentations. Thirty-day mortality ranges from 30% to 50%, significantly higher than in younger populations. Objective Identify sociodemographic, clinical, and microbiological factors associated with in-hospital mortality in adults aged ≥ 65 years diagnosed with bacteremia in a tertiary care hospital in Manizales/Colombia between 2020 and 2023. Methods A retrospective observational analytical cohort study including 400 patients with bacteremia confirmed by blood cultures. Results The population was characterized by a high burden of comorbidities, predominance of males, low educational level, and some degree of functional dependence. Overall mortality was 45%, with no significant differences between age groups. The most frequently isolated microorganisms were Gram-negative bacilli, particularly Escherichia coli and Klebsiella pneumoniae . No statistically significant association was found between antimicrobial resistance patterns and mortality. In multivariate analysis, factors independently associated with higher mortality were immunosuppression, high Charlson Comorbidity Index, coexistence of COVID-19, and abdominal source of infection. Conclusions This cohort of adults aged ≥ 65 years with bacteremia showed high mortality consistent with international reports, primarily driven by individual clinical factors such as immunosuppression, abdominal source, and COVID-19 infection during hospitalization.