What Causes Pneumonia in Adults?


Pneumonia is an infection that inflames the air sacs in one or both lungs. It can be caused by a variety of microorganisms, including bacteria, viruses, fungi, and, less commonly, parasites. Pneumonia in adults can result from various factors, and the underlying cause often determines the type of microorganism responsible. Here are some common causes of pneumonia in adults:

  • Bacterial Infections:
    • Streptococcus pneumoniae: This bacterium is a common cause of community-acquired pneumonia. It can lead to severe symptoms, especially in older adults and those with weakened immune systems.
    • Haemophilus influenzae: While it’s not the flu virus, this bacterium can cause respiratory infections, including pneumonia.
    • Mycoplasma pneumoniae: This bacterium causes a type of pneumonia known as “walking pneumonia.” It often leads to milder symptoms than other types of pneumonia.
    • Legionella pneumophila: Legionella bacteria can cause a severe type of pneumonia known as Legionnaires’ disease, often associated with water sources such as cooling towers and hot tubs.
  • Viral Infections:
    • Influenza Virus: Influenza (flu) viruses can lead to viral pneumonia, often resulting in more severe symptoms than typical flu.
    • Respiratory Syncytial Virus (RSV): RSV is a common cause of pneumonia, especially in older adults and individuals with weakened immune systems.
    • Adenoviruses: These viruses can cause a variety of respiratory illnesses, including pneumonia.
    • SARS-CoV-2: The virus responsible for COVID-19 can lead to viral pneumonia, which can range from mild to severe.
  • Fungal Infections:
    • Pneumocystis jirovecii: This fungus can cause pneumonia in individuals with weakened immune systems, such as those with HIV/AIDS or undergoing immunosuppressive therapy.
    • Histoplasma capsulatum: Inhalation of fungal spores from contaminated soil can lead to histoplasmosis, a type of fungal pneumonia.
  • Aspiration:
    • Inhaling food, liquid, or vomit into the lungs can lead to aspiration pneumonia. This is more common in individuals with impaired swallowing (dysphagia), altered consciousness, or certain medical conditions.
  • Immunosuppression:
    • Weakened immune systems due to conditions like HIV/AIDS, cancer, organ transplantation, or immunosuppressive medications can increase the risk of developing pneumonia.
  • Environmental Exposures:
    • Exposure to certain environmental factors, such as pollution, chemicals, or smoking, can increase the risk of developing pneumonia.

It’s important to note that pneumonia can range from mild to severe, and symptoms can vary widely. Common symptoms include cough, fever, difficulty breathing, chest pain, and fatigue. If you suspect you have pneumonia or are experiencing severe respiratory symptoms, it’s crucial to seek medical attention. A healthcare provider can diagnose the underlying cause of pneumonia and recommend appropriate treatment, which may involve antibiotics (for bacterial pneumonia), antiviral medications (for viral pneumonia), or other interventions based on the specific cause and severity of the infection.

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