Sunday, April 14, 2024

How is pneumonia caused?

Pneumonia is caused by infection of the lungs, which leads to inflammation of the air sacs (alveoli) and accumulation of fluid or pus within them. The infection can be caused by a variety of infectious agents, including:

Bacteria: Bacterial pneumonia is a common cause of pneumonia and can be caused by different types of bacteria. The most common bacterial cause of pneumonia is Streptococcus pneumoniae (pneumococcus), but other bacteria such as Haemophilus influenzae, Mycoplasma pneumoniae, Legionella pneumophila, Chlamydophila pneumoniae, and Staphylococcus aureus can also cause pneumonia.

Viruses: Viral pneumonia is caused by respiratory viruses, including influenza viruses (such as influenza A and influenza B), respiratory syncytial virus (RSV), adenoviruses, human metapneumovirus (hMPV), and others. Viral pneumonia is often milder than bacterial pneumonia but can still cause severe illness, especially in young children, older adults, and people with weakened immune systems.

Fungi: Fungal pneumonia is less common but can occur in individuals with weakened immune systems, such as those with HIV/AIDS, cancer, or organ transplantation. Fungal pathogens that can cause pneumonia include Pneumocystis jirovecii (formerly known as Pneumocystis carinii), Cryptococcus neoformans, Histoplasma capsulatum, and others.

Parasites: Parasitic pneumonia is rare and is typically caused by parasites such as Pneumocystis jirovecii (in immunocompromised individuals) or parasitic worms (helminths) that migrate to the lungs.

Pneumonia can develop when these infectious agents are inhaled into the lungs or enter the lungs through aspiration of oral or gastric contents (such as saliva, food, or stomach acid). Once in the lungs, the infectious agents multiply and trigger an inflammatory response, leading to the characteristic symptoms of pneumonia, such as cough, fever, difficulty breathing, and chest pain.

Risk factors for pneumonia include age (very young or very old), weakened immune system, chronic lung diseases (such as COPD or asthma), smoking, recent respiratory infections, recent surgery or hospitalization, and certain medical conditions (such as heart disease or diabetes). Prompt recognition and appropriate treatment of pneumonia are important to prevent complications and improve outcomes.


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