What are the definitions and treatment approaches for Community-Acquired Pneumonia (CAP), Hospital-Acquired Pneumonia (HAP), and Ventilator-Associated Pneumonia (VAP)?

Definitions and Treatment Approaches for CAP, HAP, and VAP

Hospital-acquired pneumonia (HAP), ventilator-associated pneumonia (VAP), and community-acquired pneumonia (CAP) are distinct clinical entities with different definitions, risk factors, causative pathogens, and treatment approaches.

Definitions

Community-Acquired Pneumonia (CAP)

• Pneumonia that occurs in patients who have not been hospitalized or resided in a long-term care facility within the previous 14 days
• Typically caused by Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, and other community pathogens

Hospital-Acquired Pneumonia (HAP)

• HAP is defined as pneumonia that occurs 48 hours or more after hospital admission and was not incubating at the time of admission 1
• Develops in patients admitted to the hospital for >48 hours with an incubation period of at least 2 days 2
• Second most common nosocomial infection and leading cause of death from nosocomial infections in critically ill patients 2

Ventilator-Associated Pneumonia (VAP)

• VAP is defined as pneumonia that develops in intensive care unit (ICU) patients who have been mechanically ventilated for at least 48 hours 2
• Distinguished from patients with severe nosocomial pneumonia who require mechanical ventilation after the onset of infection 2
• Incidence ranges from 2-16 episodes per 1000 ventilator-days 2

Healthcare-Associated Pneumonia (HCAP)

• Pneumonia that develops in non-hospitalized patients with specific healthcare-associated risk factors 2
• Risk factors include: hospitalization for ≥2 days within the preceding 90 days, residence in nursing home or extended care facility, home infusion therapy, chronic dialysis within 30 days, home wound care, or family member with multidrug-resistant pathogen 2

Diagnosis

Clinical Criteria

• HAP diagnosis requires new or progressive radiographic infiltrates on chest imaging, plus at least two of the following: fever, leukocytosis or leukopenia, and purulent secretions 1

Microbiological Diagnosis

• Lower respiratory tract samples should be collected from all patients with suspected HAP/VAP before antibiotic therapy 1
• Collection methods include:
  • Endotracheal aspirates
  • Bronchoalveolar lavage (BAL)
  • Protected specimen brush (PSB)
  • Blood cultures should be obtained in all patients with suspected VAP 1

Pathogens and Risk Factors

Early-onset HAP (<5 days of hospitalization)

• Often caused by methicillin-susceptible Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae 1
• Generally more antibiotic-sensitive organisms

Late-onset HAP (≥5 days) and VAP

• Often caused by multidrug-resistant (MDR) pathogens:
  • Enterobacteriaceae
  • Pseudomonas aeruginosa
  • Acinetobacter species
  • Methicillin-resistant S. aureus (MRSA) 1

Risk Factors for MDR Pathogens

1. Prior intravenous antibiotic use within 90 days
2. Current hospitalization of 5 days or more
3. High frequency of antibiotic resistance in the community or specific hospital unit
4. Septic shock at time of VAP
5. ARDS preceding VAP
6. Acute renal replacement therapy prior to VAP onset 2

Treatment Approaches

Empiric Antibiotic Therapy

• Treatment should be initiated promptly after obtaining cultures, as delays increase mortality 1
• Empiric therapy should be guided by:
  1. Local antibiogram data
  2. Patient risk factors for MDR pathogens
  3. Severity of illness

For Patients with Low Risk for MDR Pathogens (Early-onset without risk factors)

• Narrower spectrum antibiotics such as:
  • Ceftriaxone
  • Ampicillin-sulbactam
  • Ertapenem
  • Levofloxacin or moxifloxacin

For Patients with High Risk for MDR Pathogens (Late-onset or with risk factors)

• Broader spectrum coverage with:
  • Antipseudomonal β-lactam (piperacillin-tazobactam, cefepime, meropenem, or imipenem) 2
  • Plus MRSA coverage (vancomycin or linezolid) if risk factors present 1
  • Consider double antipseudomonal coverage in patients with septic shock, high risk of death, or high local prevalence of resistant Pseudomonas 2

De-escalation and Duration

• De-escalate therapy based on culture results and clinical response 1
• Standard duration: 7-8 days for patients with good clinical response 1
• Extended duration (10-14 days) may be necessary for:
  • Infections with non-fermenting gram-negative bacilli
  • Inadequate initial clinical response 1

Prevention Strategies

VAP Prevention Bundle

1. Elevation of the head of the bed to 30-45 degrees
2. Daily sedation interruptions and assessment of readiness to extubate
3. Deep venous thrombosis prophylaxis
4. Peptic ulcer disease prophylaxis
5. Oral care with chlorhexidine
6. Endotracheal tubes with subglottic secretion drainage

HAP Prevention

1. Hand hygiene
2. Early mobilization
3. Aspiration precautions
4. Avoiding unnecessary antibiotics

Common Pitfalls in Management

1. Overdiagnosis leading to unnecessary antibiotic use
2. Delayed therapy increasing mortality
3. Inadequate initial coverage for likely pathogens
4. Failure to obtain cultures before starting antibiotics
5. Treating colonization rather than infection
6. Failure to de-escalate therapy when appropriate 1

By understanding the definitions, causative pathogens, and treatment approaches for CAP, HAP, and VAP, clinicians can provide timely and appropriate therapy while practicing good antibiotic stewardship to improve patient outcomes and reduce the development of antimicrobial resistance.