**2. Definitions**

Hospital-acquired pneumonia (HAP) or nosocomial pneumonia refers to any pneumonia contracted by a patient in a hospital at least 48–72 h after being admitted. Community-acquired pneumonia (CAP) is defined as pneumonia acquired outside a hospital or a long-term care facility. It occurs within 48 h of hospital admission or in a patient presenting with pneumonia who does not have any of the characteristics of healthcare-associated pneumonia. The nosocomial pneumonia, which is associated with mechanical ventilation for a duration of more than 48 h, is termed as ventilator-associated pneumonia (VAP), whereas the healthcare-associated pneumonia is defined as the pneumonia occurring in non-hospitalized patients having contact with the healthcare system.
