Pneumonia is an infection that causes inflammation and fluid in the lungs. It can be caused by a variety of germs, including bacteria, viruses, and fungi. Here are some of the most common causes of pneumonia in adults:

• Bacteria: Bacteria are the most common cause of pneumonia in adults. Some of the most common types of bacteria that cause pneumonia include Streptococcus pneumoniae, Haemophilus influenzae, and Legionella pneumophila. Bacterial pneumonia can occur on its own or develop after a viral cold or the flu.

• Viruses: Viruses are another common cause of pneumonia in adults. Some of the most common viruses that cause pneumonia include influenza viruses, respiratory syncytial virus (RSV), and SARS-CoV-2 (the virus that causes COVID-19) . Viral pneumonia is often mild and goes away on its own within a few weeks, but it can be serious enough to require hospitalization.

• Fungi: Fungal pneumonia is less common than bacterial or viral pneumonia, but it can occur in people with weakened immune systems.

Pneumonia can also be caused by other factors, such as inhaling food, liquid, or chemicals into the lungs. People who are at higher risk of developing pneumonia include infants and young children, adults over the age of 65, people with underlying health conditions or weakened immune systems, and people receiving chemotherapy or taking medication that suppresses the immune system.