Outcomes of septic shock from urinary and non-urinary sources in nonagenarians and centenarians admitted to intensive care units.

Although sepsis-related mortality has declined with advances in care, the incidence of septic shock is rising by 1-8% annually. As life expectancy increases, the ≥ 90-year-old population is projected to reach 10 million in the U.S. by 2050, highlighting septic shock as a growing public health burden. Despite urinary tract infections being a common cause, non-urinary sources may carry higher mortality. However, outcome data in nonagenarians and centenarians are limited. This study compares outcomes by infection source in ICU patients aged 90 years or older with septic shock. This retrospective study, approved by the Alfred Ethics Committee (No. 253/24), used de-identified data from the ANZICS Adult Patient Database (2010-2023), including nonagenarian and centenarian ICU patients with septic shock. Variables included demographics, comorbidities, frailty, severity scores, and 24-h biomarkers. Outcomes were mortality by infection source and length of stay. Propensity score matching ensured covariate balance. Time-dependent Cox models and AUROC analysis were used. Complete case analysis was performed, with p < 0.05 considered statistically significant. Among 1095 ICU patients aged ≥ 90 with septic shock, non-urinary tract infections were associated with significantly higher short-term mortality compared to urinary sources, even after propensity matching (300-day HR 1.348; p = 0.012). ICU mortality (15.7% vs. 8.6%) and hospital mortality (29.0% vs. 17.3%) were also higher in the non-urinary group. APACHE III score, but not age or SOFA score, predicted mortality. Urine output and arterial pH were the best mortality discriminators for non-urinary and urinary sources, respectively. Higher SOFA and APACHE III scores were linked to shorter hospital stays, but not ICU length of stay. In critically ill patients aged ≥ 90 with septic shock, infection source was an independent, time-dependent predictor of mortality. Non-urinary tract infections were associated with significantly higher mortality than urinary tract infections for the first 300 days, despite comparable illness severity. These findings underscore the prognostic importance of infection source and its role in early risk stratification, triage, and end-of-life planning. Simple physiological markers, including urine output and arterial pH, demonstrated additional discriminatory value. As the very elderly ICU population grows, integrating infection source and early physiological indicators into tailored prognostic tools is essential to guide individualized, efficient care in high-resource critical care settings.