Pneumonia, Bacterial

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Bacterial pneumonia is an acute infection of the pulmonary parenchyma by a bacterial organism.

Description

Bacterial pneumonia can be classified as follows:

  • Community-acquired pneumonia (CAP); further classified by severity:
    • CAP in an outpatient setting
    • Nonsevere CAP in an inpatient setting
    • CAP in an ICU or severe CAP is based on illness severity criteria and defined as the presence of one major criterion or at least three minor criteria.
      • Major criteria: septic shock requiring vasopressors, respiratory failure requiring mechanical ventilation
      • Minor criteria: respiratory rate (RR) ≥30, PaO2/FiO2 ratio ≤250, multilobar infiltrates, confusion, BUN ≥20, WBC ≤4, platelets <100,000/μL, hypothermia, and hypotension
  • Nosocomial pneumonia: acquired in health care settings
    • Hospital-acquired pneumonia (HAP): occurs ≥48 hours after admission and did not appear to be incubating at the time of admission
    • Ventilator-associated pneumonia (VAP): develops ≥48 hours after endotracheal intubation

Epidemiology

  • In the United States, the annual incidence of CAP is 24.8 cases per 10,000 adults with higher rates as age increases. Pneumonia is the eighth leading cause of death and first among infectious causes of death.
  • Worldwide, pneumonia kills more children than any other infectious disease. Respiratory viruses are the most commonly detected causes of pneumonia.

Incidence

  • CAP: 5 to 6 cases per 1,000 persons with increased incidence occurring in the winter months
  • HAP: 5 to 20 cases per 1,000 admissions; incidence increases 6- to 20-fold in ventilated patients

Etiology and Pathophysiology

  • Adults, outpatient CAP
    • Typical (85%): Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, group A Streptococcus, Moraxella catarrhalis
    • Atypical (15%): Legionella spp., Mycoplasma pneumoniae, Chlamydophila pneumoniae
  • Adults, inpatient nonsevere or severe CAP, HAP, VAP
    • Aerobic gram-negative bacilli: Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and Acinetobacter spp.
    • Gram-positive cocci: Streptococcus spp. and S. aureus (including MRSA)
  • Pediatric
    • Birth to 3 weeks: E. coli, group B Streptococci, Listeria monocytogenes
    • <3 months: Chlamydia trachomatis, S. pneumoniae, H. influenzae
    • 3 months to 18 years: Typical: S. pneumoniae; Atypical: C. pneumoniae, M. pneumoniae

Risk Factors

  • Immunosuppression:
    • Chronic steroid use (>20 mg/day or >2 mg/kg/day of prednisone for >14 days)
    • HIV/immunoglobulin deficiencies/solid organ transplant/TNF-α inhibitor therapy
  • Chronic health conditions: asthma, COPD, type 2 diabetes mellitus (DM), chronic renal failure, CHF, liver disease, tobacco use
  • Age >65 years, antibiotic therapy in the past 6 months/resistance to antibiotics
  • Hospitalization for ≥2 days during past 90 days
  • Poor functional status

General Prevention

Vaccination recommendations:

  • All children should be vaccinated with PCV15 or 20 at 2, 4, 6, and 12 to 15 months of age.
  • Pneumococcal vaccination is recommended for all adults aged ≥65 years.
  • Adults aged 19 to 64 years with chronic diseases, defined by the CDC, should receive 1 dose of PCV20 or 21. For those who have only received PPSV23, give PCV20 or PCV21 1 year after their most recent PPSV23.
  • Annual influenza and COVID-19 vaccine

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