Pneumonia: CAP vs HAP Overview

CAP and HAP

• Community-acquired pneumonia (CAP) occurs outside the hospital or within 48 hours of hospital admission.
• Hospital-acquired pneumonia (HAP) occurs 48 hours or more after hospital admission.
• Multidrug resistance is more common in HAP.
• CAP can be caused by S. pneumoniae, H. influenzae, C. pneumoniae, M. pneumoniae, M. catarrhalis, Enteric Gram-negative bacilli, L. pneumophila, Anaerobes, S. aureus, and P. aeruginosa.
• HAP is most commonly caused by gram-negative bacilli, predominantly P. aeruginosa and the Enterobacteriaceae, or S. aureus.

Pathogenesis

• Respiratory host defenses are comprised of innate and adaptive immunity pathways.
• Healthy individuals have robust defense mechanisms, efficiently removing pathogens before infection.
• Immunocompromised individuals lack robust defense mechanisms, increasing susceptibility to infection.
• Lung infections can suppress antibacterial activity, impairing alveolar macrophage function and mucociliary clearance, leading to secondary bacterial pneumonia.

### Pathophysiology

• Urinary antigen tests detect S. pneumoniae in urine and are more rapid than traditional microbiological methods.

Physical Examination

• Tachypnea and tachycardia are common symptoms of pneumonia.
• Dullness to percussion, increased tactile fremitus, whisper pectoriloquy, and egophony are signs of pneumonia.
• Chest wall retractions and grunting respirations indicate respiratory distress.
• Diminished breath sounds over the affected area and inspiratory crackles suggest lung consolidation.

Chest Radiograph

• A dense lobar or segmental infiltrate is characteristic of pneumonia.

Laboratory Tests

• Leukocytosis with predominance of polymorphonuclear cells, elevated white blood cell count, is a common finding.
• Low oxygen saturation on arterial blood gas or pulse oximetry indicates respiratory compromise.

Management of Pneumonia

• Treatment goals: Eradication of the offending organism, minimization of unintended consequences of therapy, and minimizing costs.

General Approach to Treatment

• Antimicrobial treatment involves selecting the right antibiotic at the right time, dose, and duration.
• Continual monitoring of patient clinical status and diagnostic data guides therapy decisions, adjusting or discontinuing treatment as needed.
• CURB-65 and CRB-65 are commonly used severity assessment tools for CAP.

CURB-65

• The CURB-65 score assigns 1 point for each criterion present:
  • Confusion
  • Uremia (BUN >20 mg/dL or 7.1 mmol/L)
  • Respiratory rate ≥30 breaths/min
  • Blood pressure (systolic <90 mmHg or diastolic <60 mmHg)
  • Age ≥65 years

### Empiric Therapy for CAP

• Low risk of MRSA:
  • Ceftriaxone 2 g IV q24h OR Ertapenem 1g IV q24h PLUS Azithromycin 500mg IV daily OR Levofloxacin 750mg IV daily
• **Risk of MRSA: **
  • Piperacillin-tazobactam 4.5g IV q6h OR Cefepime 2g IV q8-12h OR Meropenem 1g IV q8h PLUS Azithromycin 500mg IV daily PLUS (Gentamicin 5-7mg/kg IV daily OR Amikacin 15mg/kg IV daily) OR (Piperacillin-tazobactam 4.5g IV q6h OR Cefepime 2g IV q8-12h OR Meropenem 1g IV q8h) PLUS (Levofloxacin 750mg IV daily OR Ciprofloxacin 400mg IV q8-12h)
• Suspected MRSA pneumonia:
  • ADD Vancomycin 25-30mg/kg loading dose then 15-20mg/kg IV q8-12h OR Linezolid 600mg IV q12h

### Duration of Treatment

• 7-10 days is usually adequate for most pneumonia cases.
• 28 days is possible for S. aureus or P. aeruginosa with concomitant.

Directed Antimicrobial Therapy for Common Pneumonia Pathogens

• S. pneumoniae: The most common bacterial cause of CAP.
  • Narrow-spectrum penicillin (penicillin, ampicillin, or amoxicillin) is preferred for susceptible strains (MIC ≤ 2 mg/L).
  • Cephalosporin, macrolides, or anti-pneumococcal fluoroquinolones are alternative options.
  • Third-generation cephalosporin or fluoroquinolone is preferred for resistant strains.
  • High-dose amoxicillin (3 g/day) may be used for intermediate strains (MIC = 4 mg/L).

### Empiric Therapy for HAP

• All empiric HAP regimens should cover gram-negative bacilli with at least one antibiotic, typically an antipseudomonal, antistaphylococcal β-lactam or an antipseudomonal, antistaphylococcal fluoroquinolone.
• MRSA coverage: If the hospital MRSA prevalence is ≥ 20%, or the patient has risk factors like IV antibiotics in the past 90 days or structural lung disease, vancomycin or linezolid should be added.
• MDR gram-negative coverage: Consider adding a second antipseudomonal agent for patients with MDR risk factors.

Directed Therapy for Important Gram-Negative Pathogens

• H. influenzae: The most common gram-negative cause of CAP.
  • For susceptible strains, oral amoxicillin is commonly used.
  • For resistant strains, oral or intravenous cefuroxime, intravenous ceftriaxone, or oral levofloxacin are options.

### Directed Therapy for MRSA Pneumonia

• Methicillin-susceptible strains:
  • Dicloxacillin is preferred.
  • Cefazolin is an alternative option with less clinical data.
  • Clindamycin or vancomycin may be used but are not preferred.
• Methicillin-resistant strains (MRSA):
  • Vancomycin or linezolid are the treatment of choice.
  • Alternatives with limited evidence:
    • Quinupristin-dalfopristin
    • Ceftaroline
    • Sulfamethoxazole-trimethoprim
    • Clindamycin

Explore the key differences between community-acquired pneumonia (CAP) and hospital-acquired pneumonia (HAP), including their common causes and associated risks. Understand the role of host defenses in the pathogenesis of pneumonia and how they impact infection susceptibility.