Hospital-acquired pneumonia (HAP) is defined as an infection of the pulmonary parenchyma that develops in patients admitted to hospital for more than 48 hours and that was not incubating at the time of admission. It represents one of the most common and serious nosocomial infections, associated with significant morbidity, prolonged hospitalisation, and increased mortality in critically ill patients.
The aetiology of HAP is primarily driven by micro-aspiration of bacteria colonising the oropharynx and upper gastrointestinal tract. Pathogen distribution is shaped by the duration of hospitalisation, prior antibiotic exposure, local epidemiology, and patient characteristics. Multidrug-resistant (MDR) organisms are particularly prevalent in patients with prolonged inpatient stay and intensive care unit (ICU) admission, as critically ill patients become rapidly colonised with nosocomial pathogens.
Ventilator-associated pneumonia (VAP), a subgroup of nosocomial pneumonia, occurs in patients requiring tracheal intubation and mechanical ventilation for at least 48 hours. A clinically important and increasingly recognised entity is ventilated HAP (v-HAP), defined as HAP that subsequently requires tracheal intubation and mechanical ventilation. Emerging evidence indicates that v-HAP carries the highest mortality among nosocomial pneumonia subtypes in ICU patients - exceeding VAP - while non-ventilated ICU-acquired HAP carries the lowest mortality.