Pneumonia Overview 

Definition: 
Pneumonia is an acute infection of the lung parenchyma that leads to inflammation of the alveoli, often filling them with fluid or pus. It can be caused by bacteria, viruses, fungi, or atypical organisms. 

Aetiology: 

1. Bacterial Pneumonia (Most common in adults) 

Streptococcus pneumoniae – most common overall (community-acquired). 
Haemophilus influenzae – most common in patients with COPD. 
Staphylococcus aureus – post-influenza, or hospital-acquired. 
Klebsiella pneumoniae – alcoholics, diabetics; classically characterised by “jelly” sputum. 
Pseudomonas aeruginosa – immunocompromised or ventilator-associated. 

2. Atypical Pneumonia 

Mycoplasma pneumoniae – “walking pneumonia,” young adults. 
Chlamydophila pneumoniae 
Legionella pneumophila – may have GI symptoms, hyponatremia. 

3. Viral Pneumonia 

Influenza, RSV, SARS-CoV-2, adenovirus. 

4. Fungal Pneumonia (immunocompromised or endemic areas) 
Histoplasma, Coccidioides, Cryptococcus. 

Classification 

Based on Setting 

Community-acquired pneumonia (CAP) 
Hospital-acquired pneumonia (HAP) 
Ventilator-associated pneumonia (VAP) 

Based on Radiology 

Lobar pneumonia – involves a lobe, often bacterial. 
Bronchopneumonia – patchy, peribronchial; bacterial. 
Interstitial pneumonia – diffuse infiltrates; viral or atypical. 
 
Pathophysiology 

Inhalation or aspiration of pathogens → alveolar infection → inflammatory response. 

Alveolar filling: exudate, neutrophils, and fibrin. 
Impaired gas exchange → hypoxemia. 
Systemic inflammatory response → fever, leukocytosis, and sometimes sepsis. 

Clinical Features 

Symptoms: 

Fever, chills 
Cough (productive or dry) 
Dyspnoea 
Pleuritic chest pain 
Fatigue, malaise 
Sometimes confusion in elderly patients 

Signs: 

Tachypnoea, tachycardia 
Crackles (rales), bronchial breath sounds 
Dullness to percussion over consolidation 
Increased tactile fremitus 

Investigations 

1. Laboratory Tests 
FBC: leucocytosis with neutrophilia (bacterial), lymphocytosis (viral) 
Blood cultures: especially if severe or hospitalized 
Sputum Gram stain and culture 
PCR for atypical pathogens or viruses 

2. Imaging 
Chest X-ray: consolidation (lobar), patchy infiltrates (bronchopneumonia), interstitial pattern (atypical) 
CT scan: reserved for complicated cases 

3. Severity Assessment 

CURB-65 score – (Confusion, Urea >7 mmol/L, Respiratory rate ≥30, Blood pressure low, Age ≥65) 
Pneumonia Severity Index (PSI) 
 
Treatment 

1. Empirical Antibiotics (CAP in adults, outpatient): 
Amoxicillin or doxycycline or macrolide (depending on local resistance) – by local guidelines 

2. Inpatient Therapy (CAP): 
IV beta-lactam + macrolide OR 
Respiratory fluoroquinolone (levofloxacin/moxifloxacin) 
Follow local guidelines 

3. HAP/VAP: 
Broad-spectrum coverage (piperacillin-tazobactam, cefepime, carbapenem) ± MRSA coverage if risk factors 
As guided by local guidelines/microbiology advice 

4. Supportive Care: 
Oxygen if hypoxic 
Fluids, analgesics, antipyretics 
Chest physiotherapy if indicated (eg; retained secretions, poor cough) 

Complications 
Parapneumonic effusion / empyema 
Lung abscess 
Respiratory failure / ARDS 
Sepsis / septic shock 
Dissemination in immunocompromised patients 

Recommend to minimise risk: 

Vaccination:
Pneumococcal vaccines (PCV13, PPSV23),
Influenza vaccine (particularly in at risk groups) 

Smoking cessation 
Good hand hygiene