Introduction
Pneumonia remains one of the leading causes of death worldwide, making it a major public health concern. It is a serious lung infection that causes inflammation and fluid or pus buildup in the alveoli (air sacs) of the lungs.
Among its different types, bacterial pneumonia—often caused by Streptococcus pneumoniae or Haemophilus influenzae type b—accounts for a significant portion of pneumonia-related deaths. While viral infections such as RSV (respiratory syncytial virus) and influenza can also cause pneumonia, bacterial forms tend to be more severe.
What Is Bacterial Pneumonia?
Bacterial pneumonia develops when harmful bacteria invade the lungs, triggering the immune system to fight back. This immune response causes inflammation and fluid or pus accumulation in the alveoli, making breathing difficult.
Certain bacterial toxins—like pneumolysin from S. pneumoniae—can directly damage lung tissue in addition to causing inflammation.
Types of bacterial pneumonia include:
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Community-acquired pneumonia (CAP): Develops outside hospital settings or within 48 hours of admission.
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Hospital-acquired pneumonia (HAP): Appears 48 hours or more after hospital admission.
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Atypical pneumonia: Caused by less common bacteria such as Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella species. Often presents with symptoms outside the lungs and is not detected by standard Gram staining.
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Ventilator-associated pneumonia (VAP): Occurs 48+ hours after starting mechanical ventilation.
Causes of Bacterial Pneumonia
The causative organisms vary depending on the setting and type of pneumonia:
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Community-acquired pneumonia: S. pneumoniae, H. influenzae, M. pneumoniae, Legionella, Moraxella catarrhalis, Staphylococcus aureus (including MRSA, often after influenza).
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Hospital-acquired pneumonia: S. aureus, Pseudomonas aeruginosa, Acinetobacter baumannii.
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Atypical pneumonia: M. pneumoniae, C. pneumoniae, Legionella pneumophila.
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Ventilator-associated pneumonia: S. aureus, P. aeruginosa, Klebsiella, E. coli, other gram-negative bacilli.
In nearly 50% of pneumonia cases, the exact cause remains unidentified—highlighting the importance of diagnostic testing.
How Does Bacterial Pneumonia Spread?
Bacterial pneumonia spreads through respiratory droplets when an infected person coughs or sneezes. You can reduce your risk by following these steps:
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Wash hands regularly with warm water and soap.
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Avoid smoking and limit alcohol intake.
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Maintain good oral hygiene.
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Manage chronic conditions (e.g., asthma) promptly.
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Stay up to date on key vaccinations:
Recommended vaccines:
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Hib (Haemophilus influenzae type b): For infants under 5 years, as per the national schedule.
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Pertussis (DTaP/Tdap): Protects against whooping cough (indirectly helps reduce pneumonia risk).
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Pneumococcal vaccines (PCV15, PCV20, PPSV23): Protect against S. pneumoniae.
Complications if Left Untreated
Untreated bacterial pneumonia can cause serious health issues, including:
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Pleural effusion: Fluid buildup around the lungs
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Empyema: Pus in the pleural space
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Lung abscess
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Breathing difficulties due to lung damage
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ARDS (acute respiratory distress syndrome) and lung scarring
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Sepsis or bacteraemia (bacteria in the blood)
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Hypoxemia (low oxygen levels)
When to See a Doctor
Seek medical attention if you have:
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Persistent cough
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Chest pain
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Difficulty breathing
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High fever
High-risk groups—including adults over 65, children under 5, and people with chronic illnesses—should seek care immediately at the first sign of symptoms.
