Bacterial and viral infections are the most common causes of pneumonia, although infections caused by other microorganisms, such as fungi and atypical bacteria, can also occur.
Pneumonia, an inflammation of the lungs, is a common respiratory disease most frequently caused by bacteria and viruses. It can occur in different forms, with symptoms including coughing, fever and difficulty breathing. Dr Zlatko Majić, a specialist in internal and emergency medicine and subspecialist in pulmonology at the International Medical Centre Priora, explains the most common causes of pneumonia, how to recognise it and the different types of the disease.
What Are the Most Common Causes of Pneumonia?
“Pneumonia encompasses a heterogeneous group of infectious and inflammatory processes affecting the lower respiratory tract and the alveoli of the lungs. It can be unilateral, affecting a smaller or larger portion of the lung tissue in one lung, or bilateral, affecting both lungs,” explains Dr Zlatko Majić, a specialist in internal and emergency medicine and subspecialist in pulmonology.
Bacterial and viral infections are the most common causes of pneumonia, although infections caused by other microorganisms, such as fungi and atypical bacteria, can also occur.
What Types of Pneumonia Are There?
Pneumonia can be classified according to various criteria. In clinical practice, the aetiological classification of pneumonia, based on the causative organism, is widely accepted:
- Bacterial pneumonia – Streptococcus pneumoniae is responsible for approximately 50% of cases.
- Viral pneumonia – accounts for approximately one-third of pneumonia cases in adults, with influenza remaining the most common cause of viral pneumonia.
- Atypical pneumonia – the most common causative organisms include Mycoplasma pneumoniae, Chlamydophila pneumoniae and Legionella pneumophila.
Based on radiological findings, pneumonia can also be classified as lobar pneumonia, bronchopneumonia or interstitial pneumonia.
How to Recognise Pneumonia
“Clinically, pneumonia most commonly presents with symptoms such as a productive cough, involving the expectoration of purulent sputum, fever, chills, shortness of breath, sharp or stabbing chest pain that worsens with deep breathing, and rapid breathing,” explains Dr Majić.
Pneumonia – What Is the Difference Between Bacterial and Viral Infections?
The main differences between bacterial (typical) and viral (atypical) pneumonia are reflected in the speed of disease progression, the type of cough, laboratory findings and treatment approaches.
Bacterial pneumonia usually begins suddenly, often accompanied by chills and shivering. It is characterised by a high fever, frequently exceeding 38.5°C or 39°C. The cough is productive, with thick, purulent, yellowish or greenish sputum. It is often accompanied by intense, sharp chest pain that worsens when taking a deep breath. C-reactive protein (CRP) levels are significantly elevated, often above 50 mg/L, and white blood cell counts are also increased. On chest X-rays, changes are usually localised to one lung. Bacterial pneumonia is treated with antibiotics, such as penicillins and macrolides.
In viral pneumonia, the onset is generally gradual, with symptoms developing over several days. Body temperature is mildly to moderately elevated, while the cough is typically dry and irritating, with little or no mucus production. Symptoms resemble those of influenza and include muscle and joint pain, headaches and general weakness. CRP levels are usually normal or mildly elevated. Chest X-rays typically show diffuse changes affecting both lungs. Treatment is generally supportive and includes rest, adequate hydration and antipyretics, or antiviral medication when indicated.
What Happens if Pneumonia Is Not Recognised in Time?
“Sometimes, viral pneumonia can weaken the immune system and lead to a secondary bacterial infection. For this reason, it is impossible to establish an accurate diagnosis or distinguish between the different types of pneumonia based solely on symptoms. A medical examination using a stethoscope, blood tests and chest imaging are essential,” concludes Dr Zlatko Majić.
