Pneumonia is the infection and inflammation of air sacs in your lungs. These air sacs, called alveoli, can fill with fluid or pus, causing a serious cough and fever. The symptoms of pneumonia can range from mild to severe, and include cough, fever, chills, and trouble breathing. Many factors affect how serious a case of pneumonia is, including what caused the infection, the person's age, and their overall health. Pneumonia is an infection of the lungs caused by bacteria, viruses, fungi, or parasites. Read on for more about the risk groups and treatments available. Pneumonia is inflammation and fluid in your lungs caused by a bacterial, viral or fungal infection. Learn the common symptoms of pneumonia , such as fever, cough and difficulty breathing, and how to prevent and treat it.