Pulmonary Infections in the Immune Competent Host

Pnuemonia

Bacterial
Viral and
Mycoplasmal

Lung Abcesses
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Bacterial pneumonia is a consolidation of the lung parenchyma that is caused by bacterial infection.

There are two types of lung consolidation. One is lobar (lobar pneumonia) in which the lobe or almost an entire lung exhibits consolidation. The other type of consolidation is a focal and bilateral as is seen in bronchopneumonia.

 

 

 

 

Pathogenesis

i) Impaired host defense mechanisms.
Loss of cough reflex, damaged mucociliary apparatus, altered phagocytic activity of alveolar macrophages, lung congestion and edema, accumulation of secretions.

ii) Altered host resistance.
Terminal illnesses, Viral infection, Chronic diseases.

iii) Other.
Inhalation of bacteria, Hematogenous spread (bacteria in blood seed the lung), Trauma, Therapeutic procedures.

 

Infectious Agents

i) Bronchopneumonia:
Staphylococci, Streptococci, Hemophilus, Pseudomonas and coliforms.

ii) Lobar Pneumonia:
Streptococcus pneumoniae (aka Pneumococci) and others.

Morphology
Gross

Lobar Pneumonia:
Consolidation of an entire lobe or large areas of the lung. The cut surface of the consolidated lung may be either red (red hepatization) or grey-yellow (grey hepatization).
[Robbins Fig 15-20, p 697]

Bronchopneumonia:
Bilateral, red gray foci of consolidation [Robbins Fig 15-17A, p 695].

Microscopic

Intraluminal neutrophils are present in bronchi, bronchioles and alveolar spaces
[Robbins Fig 15-17B, p 695; Fig 15-19, p 697].

Complications

i) Local.
Lung abscess, Bronchopleural fistula (These complications are more common in Staphylococcal pneumonia.), Pleural effusion, Empyema, Pericarditis, Suppurative mediastinitis.

ii) Distant.
Bacteremia, Metastatic abscesses in other body sites e.g., heart (endocarditis), joints (suppurative arthritis), meninges (meningitis) and brain.

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