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Pneumonia definition, predisposing factors and classification

Definition of Pneumonia
It is an acute respiratory illness characterized by inflammatory reaction within the lung parenchyma (alveoli)---> exudation into alveoli with consolidation.
Pneumonia definition

Predisposing factors :

1) Pneumococcal pneumonia often, Follows influenza or paranainfluenza Infection .
2) Cigarette smoking
3) Alcohol excess
4) IV drug abuse (staph)
5) Immunosupression.
6) Aspiration with decreased conscious level
7) Hospitalized ill patient.
8) Bronchiactasis and COPD

It is helpful to consider pneumonia in two ways  :

(a) Whether it developed at home (community-acquired) or in a hospital or institution (hospital acquired) or in immunocompromised patient.
(b) Whether it had a rapid onset with chills, fever and cough (classical) or a more gradual or indolent onset (atypical).

Classification of pneumonia :

1- Community acquired pneumonia (CAP)
a. Pneumococcal ( the commonest)
b. Staphylococci, legionella, mycoplasma (common)
c. Streptococci pseudomonas, klebsiella, H. Influenza (uncommon)
d. Chlamydia, viral e.g. influenza and parainfluenza.
2- Nosocomial pneumonia.
3- Pneumonia in Immunocompromised patient.

Pathologically, pneumonia can be classified according to the site of involvement of the lung into :
(a) Lobar pneumonia in which there is involvement of a large portion of or an entire lobe of lung. Pathological stages of lobar pneumonia are:
• Congestion with minimal exudation.
• Red hepatization with severe congestion, with alveoli full of RBCs and WBCs.
• Grey hepatization with alveoli full of leucocytes, fibrin.
• Resolution.
(b) Bronchopneumonia.
It starts as infection of bronchi and bronchioles which is aspirated into the alveoli and result in wide spread patches of consolidation, it is usually occur in lower lobes.

Lobar pneumonia can be caused by pneumococci (the main causative organism), klebsiella, staphylococci, streptococci or influenza. Bronchopneumonia caused by
staphylococci, H influenza, streptococci.


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