what causes pneumonia

Pneumonia can be caused by a wide variety of bacteria, viruses, and fungi in the air we breathe. The most common cause of bacterial pneumonia is Streptococcus pneumoniae, also known as pneumococcal pneumonia. Other bacteria such as Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Legionella pneumophila can also cause pneumonia. Viruses that infect the upper respiratory tract, such as SARS-CoV-2 (the virus that causes COVID-19) and the influenza virus, are the most common cause of viral pneumonia in adults. Respiratory syncytial virus (RSV) is the most common cause of viral pneumonia in young children. Fungi and other infections can also cause pneumonia, but they are less common