Pneumonia
Understanding lung infection, diagnosis and treatment
Pneumonia is an infection of one or both lungs in which the air sacs fill with fluid or pus, making breathing difficult. It can range from mild illness managed at home to severe, life-threatening infection requiring hospital admission. In the UK, around 220,000 people are admitted to hospital with pneumonia each year.
What is Pneumonia?
Pneumonia is an acute infection of the lung parenchyma — the tissue that carries out the lung's gas-exchange function. It causes the alveoli (tiny air sacs) to fill with fluid and inflammatory cells, impairing the transfer of oxygen into the bloodstream. Pneumonia can affect one lobe of the lung (lobar pneumonia), patches throughout the lung (bronchopneumonia), or both lungs simultaneously (bilateral or 'double' pneumonia). It is a notifiable condition when caused by certain pathogens, including Legionella and Mycobacterium tuberculosis.
Causes & Risk Factors
The most common cause of community-acquired pneumonia in the UK is Streptococcus pneumoniae (pneumococcus), accounting for approximately 30–40% of cases. Other causes include Haemophilus influenzae, Mycoplasma pneumoniae (atypical), Legionella pneumophila, respiratory viruses (including influenza and SARS-CoV-2), and Chlamydophila pneumoniae. Risk factors for developing pneumonia include older age (>65), smoking, alcohol misuse, chronic lung disease (COPD, asthma), heart failure, diabetes, immunosuppression (including HIV, long-term steroids), and recent viral respiratory tract infection. Hospital-acquired pneumonia is often caused by more resistant organisms including Pseudomonas aeruginosa and Staphylococcus aureus.
Symptoms
The classic presentation of pneumonia includes a productive cough (which may be green, yellow, rust-coloured or blood-streaked), fever and rigors (shivering), pleuritic chest pain (sharp pain that worsens on breathing in), shortness of breath, and rapid breathing (tachypnoea). Older adults or immunosuppressed patients may present atypically — with confusion, falls, reduced appetite, or simply feeling generally unwell without a prominent cough or fever. Atypical pneumonias (caused by Mycoplasma, Chlamydophila, Legionella) often present more insidiously with a dry cough, headache, and myalgia.
Diagnosis — CRB-65 Score
Diagnosis is clinical, supported by chest X-ray (consolidation) and blood tests (raised CRP, white cell count). The CRB-65 score is used in primary care to assess severity and guide management. One point is awarded for each of: Confusion (new onset), Respiratory rate ≥30/min, Blood pressure <90 systolic or ≤60 diastolic, and age ≥65. Score 0 = low risk (treat at home); score 1–2 = moderate risk (consider hospital admission); score 3–4 = high risk (urgent hospital admission). In hospital, the CURB-65 score (which includes blood urea >7 mmol/L) is used — scores ≥3 indicate severe disease requiring HDU/ITU consideration. Legionella and pneumococcal urinary antigen tests should be sent in moderate-to-severe disease.
Treatment
For mild community-acquired pneumonia managed at home (CRB-65 score 0), NICE NG138 recommends amoxicillin 500 mg three times daily for 5 days as first-line treatment. If atypical organisms are suspected (especially in younger adults), add or substitute doxycycline 200 mg day 1 then 100 mg OD or clarithromycin 500 mg twice daily for 5 days. For moderate pneumonia, consider dual therapy with amoxicillin plus a macrolide. For severe community-acquired pneumonia managed in hospital, co-amoxiclav 1.2 g IV three times daily plus clarithromycin 500 mg IV twice daily is standard. In penicillin allergy, levofloxacin 500 mg BD is an alternative. Duration is typically 5 days for mild and 7–10 days for severe disease. Response to antibiotics is usually seen within 48–72 hours.
When to go to Hospital
Seek urgent medical attention or call 999 if you or someone else has: a respiratory rate above 30 breaths per minute, oxygen saturations below 92%, new confusion or altered mental state, systolic blood pressure below 90 mmHg, or if the CRB-65 score is 2 or more. Other warning signs include central cyanosis (blue lips or fingertips), inability to maintain adequate fluid intake, and failure to improve after 48 hours of antibiotics. Older adults and young children with pneumonia should have a lower threshold for hospital admission. People who are immunosuppressed, have significant comorbidities, or live alone may also warrant admission regardless of severity score.
Prevention
Vaccination is the most effective way to prevent pneumonia. The pneumococcal vaccine (PPV23) is recommended on the NHS for all adults aged 65 and over and for those in clinical risk groups — including those with chronic lung, heart, kidney or liver disease, diabetes, immunosuppression, or asplenia. The pneumococcal conjugate vaccine (PCV13) is given as part of the childhood vaccination schedule. Annual influenza vaccination is recommended as influenza is a major risk factor for secondary bacterial pneumonia. Smoking cessation substantially reduces pneumonia risk. Good hand hygiene and respiratory hygiene (catch it, bin it, kill it) reduce transmission of respiratory pathogens.