There are 2 main types of pneumonitis:
Infectious Pneumonitis aka Pneumonia – A lung infection that causes inflammation and swelling of the air sacs in the lungs. The type of infection can vary, and may include viruses, bacteria, and fungi. Bacterial infections include Streptococcus pneumoniae, Haemophilus influenza type B, Chlamydia pneumoniae, Legionella spp., and Mycoplasma pneumoniae, while viral infections include respiratory syncytial virus (RSV) and the influenza virus.
Non-Infectious Pneumonitis – This occurs from, for example, inhaling substances or toxins that irritate the lungs. Such substances include smoke, dust, and some volatile chemicals. Additionally, certain (few) antibiotics, chemotherapy drugs, and anti-arrhythmic medications can also produce pneumonitis.