What are the criteria for diagnosing hospital-acquired pneumonia?

Criteria for Hospital-Acquired Pneumonia

Hospital-acquired pneumonia (HAP) is diagnosed when a patient develops pneumonia 48 hours or more after hospital admission, with radiological evidence of new or progressive lung infiltrates, plus specific clinical and laboratory criteria indicating infection. 1

Definition and Timing

• HAP occurs 48 hours or more after hospital admission and was not incubating at the time of admission 1, 2
• HAP is further classified into:
  • Non-ventilator HAP: occurs after 48 hours of hospital stay in non-ventilated patients 1
  • Ventilator-associated pneumonia (VAP): develops in patients mechanically ventilated for at least 48 hours 1
• Early pneumonia occurs within 5 days of admission, while late pneumonia occurs ≥5 days after admission 2

Diagnostic Criteria

HAP diagnosis requires ALL of the following components:

1. Radiological Evidence

• Two successive chest radiographs showing new or progressive lung infiltrates 2
• In patients without underlying heart or lung disease, a single chest radiograph may be sufficient 2
• Chest radiography is essential for confirming the diagnosis and differentiating from other causes 2

2. Clinical and Laboratory Signs (must have at least ONE)

• Fever >38.3°C without other cause 2
• Leukocytosis (>12,000/mm³) or leukopenia (<4,000/mm³) 2

3. Respiratory Symptoms (must have at least TWO)

• Purulent sputum 2
• Cough or dyspnea 2
• Declining oxygenation or increased oxygen requirement or need for respiratory assistance 2

Microbiological Confirmation

• Microbiological confirmation is crucial for definitive diagnosis 1, 2
• Based on qualitative or quantitative cultures of respiratory samples 2
• Pathogens are identified in approximately 70% of suspected cases 2, 1
• Other supporting tests include blood cultures and antigen detection tests 2

Common Pathogens

• Early-onset HAP (within 5 days):

  • Methicillin-susceptible Staphylococcus aureus
  • Streptococcus pneumoniae
  • Haemophilus influenzae 2, 1

• Late-onset HAP (≥5 days):

  • Enterobacteriaceae
  • Pseudomonas aeruginosa
  • Acinetobacter baumannii
  • Methicillin-resistant Staphylococcus aureus 2, 1, 3

• Polymicrobial infections occur in approximately 30% of cases 2, 3

Diagnostic Pitfalls and Considerations

• HAP is frequently overdiagnosed in clinical practice, with studies showing up to 35% of cases lack radiological confirmation 4
• Radiologically confirmed HAP represents a distinct clinical and microbiological phenotype with higher levels of inflammatory markers and sputum culture positivity 4
• Risk factors associated with radiologically confirmed HAP include previous surgery and endotracheal intubation 4
• Chest radiograph findings alone are neither highly sensitive nor specific for HAP in patients with fever, leukocytosis/leukopenia, and purulent secretions 2

Clinical Implications

• HAP is the second most common nosocomial infection after bloodstream infections and the most common infection acquired in ICUs 1
• It significantly increases healthcare costs, hospital length of stay, and mortality 1, 3
• Prompt and accurate diagnosis is essential for appropriate antimicrobial therapy and improved patient outcomes 2, 3