Types by germ:
Bacterial pneumonia: The most common cause of bacterial pneumonia is Streptococcus pneumoniae. Chlamydophila pneumonia and Legionella pneumophila can also cause bacterial pneumonia.
Viral pneumonia: Respiratory viruses are often the cause of pneumonia, especially in young children and older people. Viral pneumonia is usually not serious and lasts for a shorter time than bacterial pneumonia.
Mycoplasma pneumonia:Mycoplasma organisms are not viruses or bacteria, but they have traits common to both. Mycoplasmas generally cause mild cases of pneumonia, most often in older children and young adults.
Fungal pneumonia: Fungi from soil or bird droppings can cause pneumonia in people who inhale large amounts of the organisms. They can also cause pneumonia in people with chronic diseases or weakened immune systems.
One kind of fungal pneumonia is called Pneumocystis jirovecii pneumonia (PCP). This condition generally affects people with weakened immune systems, such as those with AIDS. In fact, PCP can be one of the first signs of infection with AIDS.