Hospital-acquired pneumonia: Past, present, and perspectives.

Hospital-acquired pneumonia (HAP) remains the most frequent and lethal hospital acquired infection, driving ICU mortality, prolonged length of stay, and resource use. Ventilator-associated pneumonia (VAP), the archetypal form of HAP, has long defined both the risks and unintended costs of intensive care. Historically, management was shaped by timelines, culture-based diagnostics, and the central role of the endotracheal tube as both lifesaving and pathogenic. This paradigm promoted rigid definitions and empiric antibiotic strategies but also generated enduring lessons on airway care, aspiration, and biofilm biology. Contemporary perspectives have shifted toward ecology and host response. The binary early-late VAP model has been replaced by a continuum of ventilatorassociated lower respiratory tract infections (VA-LRTI), from ventilator-associated tracheobronchitis to VAP. Colonisation, biofilm formation, and microbial-host interactions are now recognised as dynamic drivers of infection. Novel diagnostics-including multiplex PCR and next-generation sequencing-offer rapid pathogen and resistance detection, while biomarkers such as procalcitonin support stewardship and shorter antibiotic courses. Recognition of ventilated HAP (VHAP) has blurred traditional boundaries. Looking forward, precision diagnostics, immune monitoring, and artificial intelligence promise to integrate ecology and immunity into personalised management. The future of HAP care lies not in faster antibiotics, but in tailored, ecology-informed, host-guided strategies that improve outcomes and preserve resilience in the critically ill.