Klebsiella pneumoniae. • Common inhabitant of oral cavity (poor oral hygiene). •
Lobar pneumonia in the elderly, diabetics, alcoholics (aspiration of saliva).
Pneumonia • Acute inflammation of lung parenchyma • Inflammatory infiltrate in alveoli ( = consolidation)
CLASSIFICATION: Aetiology. Morpological class. - Bronchopneumonia vs. lobar pneumonia. Community acquired vs hospital acquired (nosocomial) infection. The patient's immune status.
AETIOLOGY • Bacteria, viruses, fungi, mycoplasma, chlamydia. •
Microbiological identification of organism often not possible.
• Previously healthy individual: → S. pneumoniae • Pre-existing viral infection → Staph. aureus or S. pneumoniae • Chronic bronchitis → Haemophilus influenzae or S. pneumoniae • AIDS → Pneumocystis carinii, cytomegalovirus, TB
Morphological classification - Bronchopneumonia - Lobar pneumonia
Bronchopneumonia: • Infants + young children and the elderly. • Usually secondary to other conditions associated with È local and general defence mechanisms: - viral infections (influenza, measles) - aspiration of food or vomitus - obstruction of a bronchus (foreign body or neoplasm) - inhalation of irritant gases - major surgery - chronic debilitating diseases, malnutrition
Lobar pneumonia: S. pneumoniae. Previously healthy individuals. Abrupt onset. Unilateral stabbing chest pain on inspiration (due to fibrinous pleurisy).
Pathology of lobar pneumonia: 4 phases: ¾Congestion Lasts < 24 hours: Alveoli filled with oedema fluid and bacteria.
¾Red hepatization • Firm, 'meaty' and airless appearance of lung. • Alveolar capillary dilatation. • Strands of fibrin extending from one alveolus to another via inter-alveolar pores of Kohn. • Also neutrophils in alveoli. • Pleura: Fibrinous exudate.
¾Grey hepatization Less hyperaemia. Macrophages, neutrophils + fibrin
¾Resolution - Lysis and removal of fibrin via sputum + lymphatics. - Begins after 8-9 days (without antibiotics). - Sudden improvement of patient's condition.
Complications of lobar pneumonia 1. Abscess formation 2. Empyema 3. Failure of resolution ⇒ intra-alveolar scarring ('carnification') ⇒ permanent loss of ventilatory function of affected parts of lung. 4. Bacteraemia: - Infective endocarditis - Cerebral abscess / meningitis - Septic arthritis
Klebsiella pneumoniae • Common inhabitant of oral cavity (poor oral hygiene). • Lobar pneumonia in the elderly, diabetics, alcoholics (aspiration of saliva).
Community acquired vs. nosocomial infection Nosocomial infection: - Often patients in ICU - ↓ Local resistance to infection in lungs - Intubation of respiratory tract - Altered normal flora due to antibiotics - E.coli, Klebsiella, Proteus, Pseudomonas, Staph. aureus.
È Immune status Infection by usually non-pathogenic organisms ('opportunistic infection') - Pneumocystis carinii - Other fungi - Cytomegalovirus (CMV)
Fig. A viral pneumonia with interstitial lymphocytic infiltrates. Note that there is no alveolar exudate. Thus, the patient with this type of pneumonia will probably not have a productive cough.
The most common causes for viral pneumonia are: • Influenza • Parainfluenza • Adenovirus • Respiratory syncytial virus (RSV) - appears mostly in children • Cytomegalovirus - in immunocompromised hosts.
Fig. RSV accounts for many cases of pneumonia in children under 2 years, and can be a cause for death in infants 1 to 6 months of age or older.
Lung abscess DEFINITION: Localised area of suppuration and tissue necrosis.
Fig. Chest X-ray. Abscess. Note air-fluid level
Aetiopathogenesis • Aspiration of infected oropharyngeal contents / vomitus. NB: Poor oral hygiene and sepsis. Ç Risk of aspiration: - Loss of consciousness (alcoholic stupor, anaesthesia, epilepsy). Oesophageal congenital atresia / fistula).
pathology
(carcinoma,
• Obstruction of bronchus - carcinoma, foreign body. • Complication of pneumonia - virulent organisms esp. Klebsiella, Staph. • Bronchiectasis. • Septic embolism (infective endocarditis on right-sided heart valves) or septisaemia. • Penetrating trauma e.g. stab wound. • Direct spread of sepsis from other organs (e.g. amoebic liver abscess).
Complications • Rupture into pleural space ⇒ empyema or broncho-pleural fistula (⇒ pyopneumothorax). • Rupture into pericardium ⇒ pericarditis. • Septisaemia ⇒ sepsis in other organs e.g. osteomyelitis, brain abscess. • Erosion of blood vessels ⇒ haemoptysis. • Organisation ⇒ fibrosis.
