What causes a person to get pneumonia?

Pneumonia is usually caused by bacteria, viruses, or fungi. Some common causes include:

• Bacteria: The most common bacterial cause of pneumonia is Streptococcus pneumoniae. Other bacteria, such as Haemophilus influenzae and Mycoplasma pneumoniae, can also cause pneumonia.

• Viruses: Respiratory viruses like the influenza (flu) virus, the virus that causes respiratory infection (RSV), and adenovirus are frequently the cause of viral pneumonia.

• Fungi: Fungal pneumonia is less common and typically affects people with weakened immune systems. Fungi such as Pneumocystis jirovecii can cause pneumonia in people with HIV/AIDS or those undergoing chemotherapy.

• Aspiration: Aspiration pneumonia occurs when foreign substances, such as food, liquids, vomit, or saliva, are inhaled into the lungs, leading to infection. This type of pneumonia is more common in people with swallowing difficulties or impaired consciousness.

• Inhalation: Inhaling harmful chemicals, smoke, or toxic fumes can irritate the lungs and lead to chemical pneumonia.

Risk factors for pneumonia include age (young children and older adults are more susceptible), a weakened immune system, chronic lung conditions (such as COPD), smoking, recent respiratory infections, and certain medical treatments (such as chemotherapy or corticosteroids).