What is HAP?
HAP (Hospital-Acquired Pneumonia) is a pneumonia that develops 48 hours or more after hospital admission and was not incubating at the time of admission. 1
Core Definition and Diagnostic Criteria
HAP is defined by the presence of a new lung infiltrate plus clinical evidence of infectious origin, including new onset of fever, purulent sputum, leukocytosis, and decline in oxygenation. 1 The diagnosis requires:
- Radiological signs: Two successive chest radiographs showing new or progressive lung infiltrates (or a single radiograph if no underlying heart/lung disease) 1
- At least one of: Body temperature >38.3°C without other cause, or leukocytes <4000/mm³ or >12,000/mm³ 1
- At least two of: Purulent sputum, cough or dyspnea, declining oxygenation or increased oxygen requirement 1
Critical Distinction from Related Conditions
HAP specifically excludes ventilator-associated pneumonia (VAP) in current terminology—these are mutually exclusive categories. 1 VAP occurs >48 hours after endotracheal intubation, while HAP denotes pneumonia in non-ventilated hospitalized patients. 1
Healthcare-associated pneumonia (HCAP) is no longer included with HAP/VAP guidelines as of 2016, because many HCAP patients are not at high risk for multidrug-resistant pathogens despite healthcare contact. 1 HCAP is now considered more appropriately addressed in community-acquired pneumonia guidelines. 1
Timing Classification
- Early HAP: Occurs <5 days after hospital admission, typically caused by methicillin-susceptible Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae 1
- Late HAP: Occurs ≥5 days after admission, more likely involving multidrug-resistant pathogens 1
Common Pathogens
The typical causative organisms include Enterobacteriaceae, Staphylococcus aureus, Pseudomonas aeruginosa, and Acinetobacter baumannii, with polymicrobial infection occurring in 30% of cases. 1
Clinical Impact
HAP is associated with high morbidity and mortality, increased duration of mechanical ventilation, prolonged ICU and hospital length-of-stay, and substantial healthcare costs. 1, 2, 3 The incidence among surgical patients with hospital stays >48 hours is approximately 1.8%. 4
Common Pitfall
Do not confuse HAP with HAPE (High-Altitude Pulmonary Edema)—these are completely different conditions. HAPE is an acute altitude-related pulmonary edema occurring in susceptible individuals exposed to hypoxia at high altitude, typically >2500m. 1, 5