Pulmonary infection

Pneumonia

• Lung infections are classified by site (e.g. lobar pneumonia or bronchopneumonia) or by aetiology

Aetiology

• Bacterial
• Viral
• Opportunistic organisms
• Chemical (e.g. aspiration of vomit)
• Radiotherapy
• Allergic mechanisms

Clinical features

• Cough
• +/- Purulent sputum
• Fever
• Pleuritic chest pain
• Breathlessness
• CURB65
• Confusion (MTS <9)
• Urea (>7 mmol/l)
• Respiratory rate (30/minute)
• Blood pressure (SBP <90 mmHg or DBP = 60 mmHg)
• Age (>65 years)

Specific features

• Streptococcus pneumoniae
• Rust-coloured sputum
• Peri-oral HSV
• Mycoplasma
• White cell count normal, cold agglutinins occur in 50%
• Extra-pulmonary complications (e.g. rash, myocarditis, pericarditis, haemolytic anaemia, myalgia, neurological abnormalities, abnormal liver function, diarrhoea)
• Staphylococcus aureus
• Abscesses - in lung and elsewhere
• Coxiella burnetii
• Multiple lesions on chest X-ray

Investigations

• Chest X-ray
• Arterial blood gases or oxygen saturation
• Blood/sputum culture
• Microbiological: urine for pneumococcal or legionella antigen, serology

Management

• Antibiotics choice depends on severity
• Mild: amoxicillin 500mg three times a day (or clarithromycin if allergic)
• Moderate: IV amoxicillin 500mg three times a day and clarithromycin twice a day
• Severe: IV cefuroxime 1.5g four times a day and clarithromycin 500mg twice a day
• Adjust as appropriate if particular organism is suspected or known
• Oxygen
• Correct/prevent dehydration

Complications

• Respiratory failure
• Type 1 - Low PaO2, low/normal PaCO2
• Lung abscess
• Particularly aspiration pneumonia, staphylococcal or klebsiella infectio, bronchial obstruction (cancer or foreign body)
• Empyema
• Pus in the pleural space

Prognosis

• Overall 5% mortality for hospital inpatients
• >25% mortality for staphylococcus aureus pneumonia
• 50% mortality for severe community acquired pneumonia