Comparison of the Clinical Frailty Scale and the FRAIL Scale for Predicting Short-Term Outcomes in Older Adults Hospitalized with Infectious Diseases: A Multicentre Prospective Study

Background Frailty is a major determinant of adverse health outcomes in older adults, yet evidence comparing commonly used frailty instruments in patients hospitalized with infectious diseases is limited. We aimed to compare the prognostic performance of the Clinical Frailty Scale (CFS) and the FRAIL Scale for predicting short-term outcomes in older adults admitted to infectious diseases departments. Methods This prospective multicentre point-prevalence study included adults aged ≥ 65 years hospitalized in infectious diseases departments across 16 hospitals in Türkiye. Frailty was assessed using the CFS (frail: ≥5) and the FRAIL Scale (frail: ≥3). The primary outcome was intensive care unit transfer, ongoing hospitalization, or death within 28 days. Multivariable logistic regression and receiver operating characteristic analyses were performed. Results Among 151 hospitalized older adults, 102 (67.5%) were classified as frail by the FRAIL Scale and 87 (57.6%) by the CFS. Polypharmacy was more common among frail patients identified by both instruments. FRAIL-defined frailty was associated with lower discharge rates (84.3% vs. 95.9%, p = 0.039) but not with mortality. In contrast, CFS-defined frailty was associated with lower discharge rates (81.6% vs. 96.9%, p = 0.004), higher 28-day mortality (8.0% vs. 0.0%, p = 0.021), and poorer overall 28-day outcomes (p = 0.032). CFS-defined frailty independently predicted poor 28-day outcome (adjusted OR 5.99, 95% CI 1.26–28.57; p = 0.024). The CFS showed greater discriminative ability than the FRAIL Scale (AUC 0.823 vs. 0.696; DeLong p = 0.034). Conclusions Both instruments identified vulnerable older adults, but the Clinical Frailty Scale provided superior prognostic performance for adverse short-term outcomes. Routine CFS assessment may facilitate early risk stratification and help identify older adults at increased risk of adverse short-term outcomes during hospitalization for infectious diseases.