Hospital-acquired Pneumonia in Adults

Background

• Hospital-acquired pneumonia (HAP) is an acute pulmonary infection that occurs ≥ 48 hours after admission into a hospital setting that is not associated with mechanical ventilation during that time.
• In the United States, HAP is the second most common nosocomial infection (after urinary tract infections), occurring in an estimated 5-10 patients per 1,000 hospital admissions.
• The specific bacterial etiology varies geographically down to the institutional level. Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA), and gram-negative rods are among the most common causes of HAP.
• Respiratory viruses, including influenza, parainfluenza, adenovirus, and respiratory syncytial virus, are also common causes of HAP.
• HAP secondary to SARS-CoV-2 has been reported, but incidence is difficult to determine as there is no accepted definition and traditional definitions likely overestimate transmission.
• Risk factors for HAP include older age, recent surgery, chronic kidney disease, altered consciousness, and aspiration.
• The primary risk factor for HAP due to a multidrug resistant organism is exposure to IV antimicrobial therapy during the preceding 90 days.
  • Hospitalization in a unit with > 20% prevalence of methicillin resistance among S. aureus isolates should be taken into account when choosing an antimicrobial regimen.
  • Structural lung disease, such as bronchiectasis or cystic fibrosis, is an additional risk factor for infection with Pseudomonas species.
• Potential complications include empyema, lung abscess, progressive respiratory failure, myocardial infarction, dysrhythmia, and sepsis.
• HAP-associated mortality may be as high as 30%, but rates vary greatly due to factors such as age, functional status, respiratory failure, pulmonary complications, sepsis, multi-organ dysfunction syndrome, recent hospitalization or antibiotic use, and immunsuppression.
• Prevention strategies include appropriate avoidance of unnecessary antibiotics when in hospital, implementation and maintenance of hospital infection control measures, vaccinations, smoking cessation, improved oral hygiene, nutritional supplementation, and preoperative inspiratory muscle training.

Evaluation

• Patients may develop fever and/or be found to have:
  • respiratory symptoms
  • secretions
  • oxygen needs
  • mental status
• Diagnosis may be confirmed by imaging criteria or criteria based on signs and symptoms.
  • Diagnosis based on imaging requires:
    • ≥ 2 serial chest x-rays with new and persistent or progressive and persistent infiltrate, consolidation, or cavitation
    • 1 definitive chest x-ray is acceptable in patients without underlying pulmonary or cardiac disease
  • A diagnosis based on signs and symptoms requires ≥ 1 of 3 clinical criteria plus ≥ 2 of 4 pulmonary criteria.
    • Clinical criteria include:
      • fever > 38 degrees C (100.4 degrees F)
      • leukopenia (< 4,000 white blood cells/mm³) or leukocytosis (≥ 12,000 white blood cells/mm³)
      • for adults ≥ 70 years old, altered mental status with no other recognized cause
    • Pulmonary criteria include:
      • new-onset purulent sputum or change in character of sputum or increased respiratory secretions or increased suctioning requirements
      • new-onset or worsening cough, dyspnea, or tachypnea
      • rales or bronchial breath sounds
      • worsening gas exchange, such as oxygen desaturations, increased oxygen requirements, or increased ventilator demand
• Obtain a complete blood count (CBC) with differential, basic metabolic panel, chest x-ray (if not already obtained), lower respiratory tract samples for Gram stain and culture, and blood cultures.
• Additional tests to consider include:
  • blood gas analysis if there is a concern for an impending respiratory failure
  • urinary antigen testing if Streptococcus pneumoniae or Legionella infection is suspected
  • respiratory virus polymerase chain reaction (PCR)
  • computed tomography if underlying lung pathology (for example bronchiectasis or obstructing neoplasm) or complications (such as empyema or lung abscess) suspected

Management

• Select an empiric antibiotic regimen based on local epidemiology, the severity of illness, and patient risk factors for multidrug-resistant organisms, then narrow coverage once sputum and blood culture results are available.
• For patients at low risk for mortality (those without impending septic shock or a need for mechanical ventilation):
  • treat with a single agent that targets methicillin-susceptible Staphylococcus aureus (MSSA), Pseudomonas, and gram-negative bacteria (Strong recommendation), such as:
    • piperacillin-tazobactam 4.5 g IV every 6 hours
    • cefepime 2 g IV every 8 hours
    • levofloxacin 750 mg IV every 24 hours
    • a carbapenem such as imipenem 500 mg IV every 6 hours or meropenem 1 g IV every 8 hours
  • if risk factors for MRSA are present, add 1 of the following (Strong recommendation)
    • vancomycin 15 mg/kg IV every 8-12 hours
    • linezolid 600 mg IV every 12 hours
• For patients at high risk for mortality, or who have received IV antibiotics in the past 90 days, or who have other risk factors for Pseudomonas infection or multidrug-resistant pathogens:
  • consider using 2 of the following agents (1 beta-lactam or beta-lactam like agent plus 1 non-beta-lactam) (Weak recommendation)
    • beta-lactam and beta-lactam like
      • piperacillin-tazobactam 4.5 g IV every 6 hours
      • cefepime or ceftazidime 2 g IV every 8 hours
      • imipenem 500 mg IV every 6 hours or meropenem 1 g IV every 8 hours
      • aztreonam 2 g IV every 8 hours
    • non-beta-lactam
      • levofloxacin 750 mg IV every 24 hours or ciprofloxacin 400 mg IV every 8 hours
      • aminoglycosides such as tobramycin 5-7 mg/kg/day IV or amikacin 15-20 mg/kg/day IV
  • Add either vancomycin or linezolid, dosed as above.
• Definitive therapy should be tailored to the infecting pathogen, if it can be identified (Weak recommendation).
• The duration of therapy is 7 days for most patients (Strong recommendation).