Community acquired pneumonia

1. - Bhargavi .P
HS20MB0022
Community Acquired Pneumonia
Pathogenesis and Risk factors

2. Pathophysiology
• Until recently it was thought that the lungs were sterile.
• New pathogens entered lower respiratory tract through micro
aspiration of oro-pharyngeal organisms and also had ability to
overcome innate & adaptive immunity, resulting in pneumonia.
• Now it has been observed that there is a diverse community of
bacteria in the lungs that constitutes Lung micro biota.

3. Pathogenesis
• Entry:
• (i) through Impaired mechanical factors
• (ii) through Bacteria

4. Pathogenesis
• (i) Entry through Impaired mechanical factors like..
• Hairs
• Turbinates of the nares
• Branching tracheobronchial tree
• Muco ciliary clearance
• Gag reflex
• Cough reflex, etc.,

5. Pathogenesis
• (ii) Entry through Bacteria
• Bacteria have easy access to lower airways through
• Inhalation
• Micro-aspiration
• Direct mucosal dispersion

6. Positive Feedback Loop:

7. Pathogenesis
• In CAP and HAP, trigger may be..
• viral infection with added micro aspiration of Oro-pharyngeal
organisms
At this stage,
Innate & Acquired immunity has
the potential to prevent the development of Pneumonia

8. If Positive feedback loop persists, then
• IL-6, TNF ------------------------------------------→ Fever
• IL-8, Granulocyte colony stimulating factor → increase in neutrophils &
macrophages → alveolar capillary Leak
↓
 Impaired Oxygenation
 Hypoxemia
 Infiltrates
 ↓ Lung compliance
 ↑ Respiratory drive
 ↑ Secretions
Worsening Dyspnea
&
Respiratory failure
------------------→

9. Morphological stages of Pneumonia
1. Congestion
2. Red hepatization
3. Gray Hepatization
4. Resolution

10. 1. Congestion
 This stage last less than 24 hrs
Gross appearance:
 Lungs are heavy, boggy & red, blood-stained frothy fluid
oozes from cut surface
Microscopy:
 Dilatation & Congestion of capillaries in the alveolar walls
 Mild Edema can be seen

11. 2. Red Hepatization
 It last for 2-3 days
Gross appearance:-
 Lungs appear red, firm, airless which resembles liver; Pleura
show serofibrinous pleurisy.
Microscopy:-
 Alveoli show exudate and interlacing strands of fibrin
 Numerous neutrophils and red cells are found in the fibrin
meshwork.

12. 2. Red Hepatization

13. 3. Gray Hepatization
 Seen on 5–7 days.
Gross appearance
 Lungs appear gray
 Cut surface shows gray, dry granular appearance
Microscopy
Progressive disintegration of red cells
Fibrino-suppurative exudate in the alveoli in which neutrophils
are replaced by macrophages

14. 3. Gray Hepatization
 There is a clear space between the alveolar wall and the
exudate due to contraction of the fibrin thread
 There is successful containment of the infection and
improvement in gas exchange.

15. 4. Resolution
 Liquefaction of the previously solid, fibrinous constituents of the
exudate in the air spaces
 To produce granular and semifluid debris
 Liquefied material is removed, partly by expectoration, but
mainly ingested by macrophages & drained through lymphatics.
Gross appearance
 The affected lobe becomes more crepitant as the air spaces
reopen.
 Cut section appears frothy

16. 4. Resolution
Microscopy:
 The alveolar space shows
 Granular material and
 Semifluid debris.

17. Risk Factors
In general:
•  Alcoholism,
•  Asthma,
•  Immunosuppression
•  Institutionalization

18. Risk Factors
• In the case of age >70 years:
• Decreased cough
• Gag reflexes
• Reduced antibody
• Toll-like receptor responses
• increase the likelihood of pneumonia

19. Risk Factors for Pneumococcal Pneumonia
 Dementia
 Seizure disorders
 Heart failure
 Cerebrovascular disease
 Alcoholism
 Tobacco smoking
 Chronic obstructive pulmonary disease (COPD) and
 HIV infection

20. Risk Factors for Enterobacteriaceae
 Hospitalization
 Treated with antibiotics
 Comorbidities such as alcoholism, heart failure or renal failure
for Pseudomonas aeruginosa
 Severe structural lung disease

21. Risk Factors for Enterobacteriaceae
for Legionella
 Diabetes
 Hematologic malignancy
 Cancer
 Severe renal disease
 HIV Infection
 Smoking
 Male gender, etc.

22. Thank you