Pathogenesis

  • CAP is an infectious process resulting from the invasion and overgrowth of microbial pathogens in lung parenchyma that overcome host defenses and provoke alveolar inflammation. CAP is characterized by complex host-pathogen interactions, which determine the extent of infection and tissue damage.1,2
  • Community-acquired pneumonia (CAP) is commonly caused by bacterial species such as Streptococcus pneumoniae that colonize the mucosa of the upper respiratory tract.1,2
  • Micro-aspiration of upper respiratory tract secretions can lead to infection of the lung parenchyma in the lower airways.1,2
Pathogenesis
Development
Illustration of CABP Pathogenesis

How Does Community-Acquired Pneumonia (CAP) Develop?

CAP is an infectious process resulting from the invasion and overgrowth of microbial pathogens in lung parenchyma that overcome host defenses and provoke alveolar inflammation. CAP is characterized by complex host-pathogen interactions, which determine the extent of infection and tissue damage.1,2

 

CAP is commonly caused by the micro-aspiration of contaminated secretions containing infectious bacteria from the upper respiratory tract.1,2 The epithelium provides a physical barrier to infection and expresses antimicrobial peptides to kill extracellular bacteria.2 Invasive bacterial species such as Streptococcus pneumoniae can enter the body via breathing and colonize the mucosa of the upper respiratory tract.1,2

 

The presence of bacteria in the lower airways triggers an immune response resulting in inflammation of and accumulation of fluids and pus in the alveoli and inflammation of the alveolar walls and bronchioles.1-3 The consequences of this damage are the symptoms of pneumonia, such as shortness of breath and chest pain.3 Based on the area of the lung involved, pneumonia can be classified histologically into lobular, lobar, bronchopneumonia, or interstitial.3

Illustration of CABP Pathogenesis

CAP Pathogenesis

Image adapted from www.uptodate.com/contents/image?imageKey=ID%2F118722&topicKey=ID%2F117561&source=see_link.

Learn about the epidemiology of CAP

References

  1. Weiser JN, Ferreira DM, Paton JC. Streptococcus pneumoniae: transmission, colonization and invasion. Nat Rev Microbiol. 2018;16(6):355–367.
  2. Grousd JA, Rich HE, Alcorn JF. Host-pathogen interactions in gram-positive bacterial pneumonia. Clin Microbiol Rev. 2019;32(3).
  3. National Institute of Health. Pneumonia. Available from: https://www.nhlbi.nih.gov/health-topics/pneumonia (accessed October 09 2020).
  4. van der Poll T, Opal SM. Pathogenesis, treatment, and prevention of pneumococcal pneumonia. Lancet. 2009 Oct 31;374(9700):1543–56.
  5. Jain V, Vashisht R, Yilmaz G, et al. Pneumonia Pathology. [Updated 2021 Mar 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing;: 2021 Jan-. Available from: Pneumonia Pathology - StatPearls - NCBI Bookshelf (nih.gov)
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