Pneumonia, Bacterial


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


Bacterial pneumonia can be classified as the following:

  • Community acquired pneumonia (CAP) is classified by severity:
    • CAP in an outpatient setting
    • Nonsevere CAP in an inpatient setting
    • CAP in an intensive care unit (ICU) or severe CAP is based on illness severity criteria and is 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 breaths/min, PaO2/FiO2 ratio ≤250, multilobar infiltrates, confusion, BUN ≥20, WBC ≤4, platelets <100,000, hypothermia, and hypotension requiring aggressive fluid resuscitation
  • 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


  • 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 is the first among infectious causes of death.
  • Worldwide, pneumonia kills more children than any other infectious disease, claiming the lives of >700,000 children aged <5 years every year. Respiratory viruses are the most commonly detected causes of pneumonia.


  • 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 sp., Mycoplasma pneumoniae, Chlamydophila pneumoniae
  • Adults, inpatient nonsevere or severe CAP, HAP, VAP
    • Aerobic gram-negative bacilli: Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and Acinetobacter sp.
    • Gram-positive cocci: Streptococcus sp. 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 2 to 59 months of age should be vaccinated with pneumococcal conjugate (PCV13); given at 2, 4, 6, and 12 to 15 months of age
  • Pneumococcal vaccination is recommended for all adults aged ≥65 years. For those who have never received vaccine before, give 1 dose of PCV20. For those with previous vaccination in adulthood, additional vaccinations are recommended per the Centers for Disease Control and Prevention (CDC)
  • Adults aged 19 to 64 years with chronic diseases, defined by the CDC, should receive 1 dose of PCV20. For those who have only received PPSV23, give PCV20 1 year after their most recent PPSV23.
  • Annual influenza vaccine

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