Pneumonia — Causes, Diagnosis and Treatment

A patient walks in with a cough that has lasted several days, now with fever and a sharp pain on breathing in. One of the first things I think about is pneumonia.

Pneumonia is an infection of the lung tissue in which the air sacs (alveoli) fill with fluid or pus. It ranges from a mild illness treated at home to a life-threatening one needing intensive care. Most cases I see are community-acquired pneumonia (CAP), meaning it developed outside a hospital.

What causes pneumonia?

Pneumonia can be caused by bacteria, viruses, or, less commonly, fungi. Streptococcus pneumoniae is the most common bacterial cause of CAP. Other bacteria include Haemophilus influenzae and the "atypical" organisms such as Mycoplasma pneumoniae and Legionella. Viruses, including influenza, RSV, and SARS-CoV-2, are also important causes, and a viral illness can pave the way for a secondary bacterial infection.

Risk is higher in adults over 65, young children, smokers, and people with COPD, diabetes, heart disease, or weakened immunity.

Symptoms to watch for

• Cough, with or without yellow, green, or rusty sputum
• Fever, chills, and sweating
• Shortness of breath or fast breathing
• Chest pain that worsens with breathing or coughing
• Fatigue and loss of appetite

Older adults may not have a fever at all. Sometimes the only sign is new confusion, which is why I take it seriously in elderly patients.

How is pneumonia diagnosed?

Diagnosis starts with the history and examination. I listen for crackles or bronchial breathing and check the respiratory rate and oxygen saturation.

Chest X-ray

A chest X-ray is the standard test to confirm the diagnosis. It typically shows a consolidation, an area of lung that appears white, and also helps identify complications such as a pleural effusion.

Laboratory tests

A complete blood count, CRP, and kidney function tests are commonly ordered. In hospitalized patients, blood cultures and sputum cultures may be sent, along with urinary antigen tests for pneumococcus and Legionella when indicated. Many mild cases need no extensive testing.

Assessing severity with CURB-65

Deciding where to treat a patient is just as important as choosing the drug. The CURB-65 score gives one point for each of the following:

• Confusion (new)
• Urea above 7 mmol/L (BUN above 19 mg/dL)
• Respiratory rate of 30 or more per minute
• Blood pressure low (systolic below 90 or diastolic 60 or less)
• Age 65 or older

A score of 0–1 generally suggests outpatient care, 2 suggests considering hospital admission, and 3 or more indicates severe pneumonia, with ICU assessment for scores of 4–5. The score supports clinical judgment but does not replace it.

Treatment

Bacterial pneumonia is treated with antibiotics. For otherwise healthy outpatients, the ATS/IDSA guideline suggests options such as amoxicillin or doxycycline. Patients with comorbidities, or those admitted to hospital, usually receive a combination such as a beta-lactam plus a macrolide, or a respiratory fluoroquinolone alone. Treatment typically lasts a minimum of 5 days, and patients should be clinically stable before stopping.

Supportive care matters too: fluids, rest, paracetamol for fever and pain, and oxygen when saturation is low. Most people feel better within a week, though fatigue and cough can linger for weeks.

Prevention

• Pneumococcal vaccination for children and at-risk adults
• Yearly influenza vaccine, plus COVID-19 and RSV vaccines where recommended
• Regular handwashing
• Quitting smoking and limiting alcohol
• Good control of chronic conditions like diabetes and COPD

Seek urgent care if you have trouble breathing, bluish lips, persistent high fever, chest pain, or confusion.