Healthcare-Associated Infections (HAIs) in the Elderly: Molecular Mechanisms of Immunosenescence and Clinical, Nutritional and Therapeutic Implications

Healthcare-associated infections (HAIs) in the elderly represent a growing clinical and public health concern, primarily driven by age-related biological remodeling. Key mechanisms include immunosenescence, inflammaging, gut microbiota dysbiosis, and profound metabolic and epigenetic alterations, all of which progressively weaken host defense and resilience to pathogens. In this review, we delineate the molecular pathways underlying these processes, with particular attention to impaired innate and adaptive immune responses, dysfunctional cellular signaling, and disrupted immunometabolic networks that increase susceptibility to multidrug-resistant organisms and aggravate clinical outcomes in older patients. We also address the synergistic impact of frailty-related factors such as malnutrition, multimorbidity, and polypharmacy on infection risk. Finally, we discuss emerging translational perspectives, including nutritional interventions and microbiota-targeted strategies aimed at restoring immune competence and reducing infection burden. By integrating molecular mechanisms with clinical implications, this review highlights innovative opportunities for personalized prevention and management of HAIs in the aging population.