Pneumonia, Bacterial


Bacterial pneumonia is an 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 validated 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 ≥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 as of 2018, CAP is the eighth most common cause of death (even higher in those >65 years).
  • Rates of infection are 3 times higher in African Americans than in whites and are 5 to 10 times higher in Native American adults and 10 times higher in Native American children.
  • Mortality rate in children is approximately 1.6 million a 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
  • Other:
    • 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 routinely vaccinated with pneumococcal conjugate (PCV13); given at 2, 4, and 6 months of age; a fourth dose at 12 to 15 months of age
  • Adults ≥65 years who are vaccine naïve: should receive PPSV23 only. Adults >65 years in the high-risk group should receive PCV13 followed by pneumococcal polysaccharide (PPSV23) ≥1-year interval.
  • For high-risk adults ≥65 years who have already received PPSV23, a dose of PCV13 is indicated after ≥1 year.
  • Adults 19 to 64 years with tobacco use, chronic heart or lung disease, alcoholism, or chronic liver disease should receive a dose of PPSV23, followed by PCV13 at age 65 years and a subsequent PPSV23 ≥1 year after PCV13 and at least 5 years after the previous PPSV23 dose.
  • High-risk adults ≥19 years old with immunocompromising conditions: Asplenia, CSF leaks, cochlear implants, HIV infection, immunodeficiencies require additional vaccinations as per the Centers for Disease Control.
  • Annual influenza vaccine

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