When is pneumonia considered hospital-acquired pneumonia (HAP)?

Definition of Hospital-Acquired Pneumonia (HAP)

Hospital-acquired pneumonia (HAP) is defined as pneumonia that occurs 48 hours or more after hospital admission, which was not incubating at the time of admission. 1, 2

Diagnostic Criteria for HAP

HAP is characterized by:

• Radiological evidence: Two successive chest radiographs showing new or progressive lung infiltrates (one radiograph is sufficient in patients without underlying heart or lung disease) 1, 2
• At least one of the following systemic signs:
  • Fever > 38.3°C without other cause 1
  • Leukocytes < 4000/mm³ or > 12,000/mm³ 1
• And at least two of the following respiratory signs:
  • Purulent sputum 1, 2
  • Cough or dyspnea 1, 2
  • Declining oxygenation or increased oxygen requirement or need for respiratory assistance 1, 2

Classification of HAP

HAP can be further classified into:

• Non-ventilator HAP: Occurs after 48 hours of hospital stay in non-ventilated patients 1, 2
• Ventilator-associated pneumonia (VAP): Develops after 48 hours of mechanical ventilation 1

Based on timing of onset, HAP can be categorized as:

• Early-onset HAP: Occurs within 5 days of hospital admission 1
• Late-onset HAP: Occurs 5 days or more after hospital admission 1

Microbiological Considerations

The pathogens responsible for HAP vary based on timing:

• Early-onset HAP (< 5 days): Usually caused by community-acquired pathogens 2

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

• Late-onset HAP (≥ 5 days): More likely to involve multidrug-resistant organisms 2

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

Clinical Significance

• HAP is the second most common nosocomial infection and the most common infection acquired in intensive care units 2, 3
• It significantly increases morbidity, mortality, hospital length of stay, and healthcare costs 1, 2
• The infection is polymicrobial in approximately 30% of cases 1
• Microbiological confirmation is crucial for definitive diagnosis and is based on cultures of respiratory samples 1, 2

Common Pitfalls to Avoid

• Misclassification: Ensure that pneumonia symptoms were not present or incubating at the time of admission 1
• Delayed diagnosis: Early recognition is essential for appropriate management and improved outcomes 4
• Inadequate sampling: Proper respiratory samples are needed for accurate microbiological diagnosis 1
• Overtreatment: Not all HAP patients require broad-spectrum antibiotics; therapy should be tailored based on risk factors for resistant organisms 5

Remember that the 48-hour timeframe is the key defining characteristic that distinguishes HAP from community-acquired pneumonia, along with the absence of incubating infection at the time of admission 1, 2.