what is pneumonia disease

Pneumonia is an infection that inflames the air sacs in one or both lungs, causing them to fill with fluid or pus. It can be caused by bacteria, viruses, or fungi, and is often spread via coughing, sneezing, or even breathing. The symptoms of pneumonia can range from mild to severe and may include a cough that produces thick, blood-tinged or yellowish-greenish sputum with pus, fever, chills, and difficulty breathing. Pneumonia can affect anyone, but it is most serious for infants and young children, people older than age 65, and people with weakened immune systems