Overview
Pneumonia is infection of the lung parenchyma, causing the air sacs (alveoli) to fill with fluid or pus. It can range from mild (community-acquired pneumonia managed at home) to life-threatening (requiring ICU admission). Streptococcus pneumoniae is the most common bacterial cause. Viruses, including influenza and SARS-CoV-2, are also important causes.
How common is it?
Pneumonia affects approximately 5 to 11 adults per 1,000 per year in the UK. About 1 in 3 people admitted to hospital with pneumonia will die within 30 days. It is the leading infectious cause of death in children globally.
Causes and risk factors
Pathogens reach the lung by inhalation or aspiration. Host defences normally clear the lower airways, but when these are overwhelmed — due to virulence of the organism or reduced immunity — infection is established.
Common risk factors
- Bacterial: Streptococcus pneumoniae (most common), Mycoplasma pneumoniae, Haemophilus influenzae, Legionella pneumophila, Staphylococcus aureus
- Viral: influenza, RSV, SARS-CoV-2, parainfluenza, rhinovirus
- Aspiration: swallowing disorders, reduced consciousness, alcohol
- Risk factors: age (very young and very old), smoking, COPD, diabetes, immunosuppression, heart failure, recent influenza, hospital exposure (hospital-acquired pneumonia)
Symptoms
- Productive cough with yellow, green, or rust-coloured sputum
- Fever with rigors
- Pleuritic chest pain (sharp, worse on breathing and coughing)
- Breathlessness
- Fatigue and malaise
- Confusion (especially in elderly — often the only presenting feature)
- Haemoptysis (in severe cases)
- Reduced oxygen saturations
When to see a doctor
See a doctor for new productive cough with fever. Go to A&E immediately for breathlessness, rapid breathing, confusion, persistent pleuritic chest pain, or oxygen saturations below 94%.
Diagnosis
CRB-65 (Confusion, Respiratory rate, Blood pressure, age 65+) or CURB-65 score guides severity and admission decision. Chest X-ray shows consolidation. Blood tests: FBC, CRP, renal function. Blood cultures and sputum culture in hospitalised patients. Pneumococcal and Legionella urinary antigen tests.
Treatments
Antibiotics
Community-acquired pneumonia: amoxicillin 500mg three times daily first-line (5 day course for mild, 7 days for moderate). Doxycycline if atypical organisms suspected. Severe: co-amoxiclav with a macrolide or IV beta-lactam.
Supportive care
Paracetamol for fever, adequate hydration, oxygen therapy to maintain saturations 94 to 98%, and bed rest during the acute phase.
Hospitalisation and escalation
Patients with CURB-65 score 2 or above need hospital assessment. ICU for haemodynamic instability or respiratory failure (mechanical ventilation or high-flow nasal cannula).
Self-care and lifestyle
- Stay well hydrated to help clear secretions
- Rest during the acute illness
- Stop smoking — smoking is the single biggest risk factor for community-acquired pneumonia in adults
- Do not return to strenuous activity until fully recovered (usually 4 to 6 weeks)
Prevention
Pneumococcal vaccine (PCV13 and PPSV23) and annual influenza vaccine are recommended for all adults over 65, people with chronic health conditions, and immunocompromised individuals. Smoking cessation and hand hygiene reduce pneumonia risk.